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mimnermus
2011-Aug-18, 06:53 PM
hi,
i'm also new,but minus Simore79's bravery which he's going to need by the look of it.i suppose i am looking for a little enlightenment,of which there would seem to be a plentiful supply. so,(gulp),is it possible that we are the other side of a black hole,any huge black hole and i hope i will not be required to explain it's origin because we can't really explain our own origin can we?
i hope no one will object to me bringing the discussion down to my level,for verily it has been said that, 'a fool may ask a wise man a question he cannot answer' and i certainly qualify here.
one thing which has always puzzled me is the certainty with which it is stated that the universe is 13.6 billion years old, this seems to be based on the fact that this is the farthest we can see in light years to the, 'horizen', and this, 'horizen', seems to be to extend in any direction all around us, which in turn seems to suggest that we are the centre of the universe,as this seems to be a little unlikely i wonder if someone could possibly elucidate.
if there is an horizen which we have reached since BB, then surely there must have been a place of origin, shall we call it a,'singularity', does any one have any idea where we might start to look for it?.

pzkpfw
2011-Aug-19, 02:17 AM
Above post moved from here: http://www.bautforum.com/showthread.php/119370-Big-Bang-Theory

At BAUT we have a fairly narrow one-thread one-topic style, and in ATM the topic of the thread is direct discussion of the claim by the person who started that thread. Thus your post was technically a hijack.

As you are not actually ready to propose these ideas as fully-fledged theories, they seem better placed here in Q&A where they can be treated as questions to be answered with mainstream science. Please do not argue against those answers (but feel free to ask for clarifications or further details.)

Tensor
2011-Aug-19, 03:01 AM
First of mimnermus, welcome to BAUT.


hi,
i'm also new,but minus Simore79's bravery which he's going to need by the look of it.i suppose i am looking for a little enlightenment,of which there would seem to be a plentiful supply. so,(gulp),is it possible that we are the other side of a black hole,any huge black hole and i hope i will not be required to explain it's origin because we can't really explain our own origin can we?

There are several subtle mathematical reasons for concluding that the universe is not a black hole (nor a white hole). Quickly, objects within General Relativity have what are called world lines. These lines describe how the objects moves through spacetime. In a black hole, the singularity is where all world lines end. In the Big Bang singularity, it's where all world lines begin. Another way of saying this is that a Black Hole singularity is always in the future, the Big Bang singularity is always in the past. This site (http://www.weburbia.com/physics/universe.html) may answer some of your questions more fully.


i hope no one will object to me bringing the discussion down to my level,for verily it has been said that, 'a fool may ask a wise man a question he cannot answer' and i certainly qualify here.
one thing which has always puzzled me is the certainty with which it is stated that the universe is 13.6 billion years old, this seems to be based on the fact that this is the farthest we can see in light years to the, 'horizen', and this, 'horizen', seems to be to extend in any direction all around us, which in turn seems to suggest that we are the centre of the universe,as this seems to be a little unlikely i wonder if someone could possibly elucidate.
if there is an horizen which we have reached since BB, then surely there must have been a place of origin, shall we call it a,'singularity', does any one have any idea where we might start to look for it?.

The quick answer is we can't see all the way back to Big Bang. This is due to the universe being opaque to light until 380,000 after the BB. It was at this point that the temperature was cool enough to allow electrons to be captured by protons to form neutral hydrogen. Until this happened, photons could not travel very far without interacting with a proton or electron. So, we can't look back any farther, as any EM would be blocked by the Protons and Electrons. Ned Wright's Cosmological Tutorial ( http://www.astro.ucla.edu/~wright/cosmology_faq.html) should help answer some questions.

korjik
2011-Aug-19, 03:01 AM
hi,
i'm also new,but minus Simore79's bravery which he's going to need by the look of it.i suppose i am looking for a little enlightenment,of which there would seem to be a plentiful supply. so,(gulp),is it possible that we are the other side of a black hole,any huge black hole and i hope i will not be required to explain it's origin because we can't really explain our own origin can we?
i hope no one will object to me bringing the discussion down to my level,for verily it has been said that, 'a fool may ask a wise man a question he cannot answer' and i certainly qualify here.
one thing which has always puzzled me is the certainty with which it is stated that the universe is 13.6 billion years old, this seems to be based on the fact that this is the farthest we can see in light years to the, 'horizen', and this, 'horizen', seems to be to extend in any direction all around us, which in turn seems to suggest that we are the centre of the universe,as this seems to be a little unlikely i wonder if someone could possibly elucidate.
if there is an horizen which we have reached since BB, then surely there must have been a place of origin, shall we call it a,'singularity', does any one have any idea where we might start to look for it?.

We shall not call it a singularity, cause it wasnt really a singularity any more than it was a bang.

All locations in the universe are the center of the universe, since they were all at the center of the universe when the universe began.

astromark
2011-Aug-19, 08:35 AM
We, the science community and those interested in this BIG question are adamant and sure that by direct observation,

and the study of information attained that the Universe as a whole is expanding at a ever increasing rate.

That only gravity bound objects are the exception to this fact.

That would not be in conductance with the workings of a Black Hole. Therefore we are not in or part there of one.

tnjrp
2011-Aug-19, 09:08 AM
i suppose i am looking for a little enlightenment,of which there would seem to be a plentiful supply. so,(gulp),is it possible that we are the other side of a black hole,any huge black hole and i hope i will not be required to explain it's origin because we can't really explain our own origin can we?The so-called fecund universe hypothesis, perhaps most famously championed by Lee Smolin, does specifically state our universe has sprung from a black hole in another, earlier universe. It doesn't however in any way go against the standard Big Bang theory as the latter is a theory concerning cosmological evolution, not the origin of cosmos.


one thing which has always puzzled me is the certainty with which it is stated that the universe is 13.6 billion years old, this seems to be based on the fact that this is the farthest we can see in light years to the, 'horizen'It is not the farthest we can see in light years, but a common misconception thereof. In fact we can see much further off because of the inflation that took place in the early state of the universe we currently observe.


this, 'horizen', seems to be to extend in any direction all around us, which in turn seems to suggest that we are the centre of the universeIn the standard cosmologicial evolution model this is taken to imply that the inflation happened uniformly accross all of the existing space-time and therefore, as Korjik said above, every point in the existing universe is equally much or equally little the center of the universe. The Finnish astronomer Esko Valtaoja is fond of saying that the Big Bang happened at the tip of his nose and he is in a sense completely correct.


if there is an horizen which we have reached since BB, then surely there must have been a place of origin, shall we call it a,'singularity', does any one have any idea where we might start to look for it?.We don't want to be hasty and call the origin of the cosmos singularity at this time...

You may be struggling under a misconception based off of the famous balloon analogy. In that analogy, the center of the baloon is not to seen as a spatial point of origin, but a temporal one. The surface of the balloon in turn is the two-dimensional projection of the 3 spatial dimensions of the universe. Once this is understood, that analogy is usefull and no longer confusing.

Jeff Root
2011-Aug-19, 11:42 AM
one thing which has always puzzled me is the certainty with
which it is stated that the universe is 13.6 billion years old,
this seems to be based on the fact that this is the farthest
we can see in light years to the 'horizen'
It is not the farthest we can see in light years, but a common
misconception thereof. In fact we can see much further off
because of the inflation that took place in the early state of
the universe we currently observe.
I think it is reasonable to say that a distance of 13.7 billion
light-years (the figure I generally use) is the farthest we can
see. It would also be reasonable to say that the farthest we
can see is much less than 13.7 billion light-years.

The cosmic background radiation -- the light from the "moment
of recombination", when protons and electrons combined to form
neutral hydrogen atoms and the Universe became transparent --
traveled a distance of 13.7 billion light-years to reach us. That
is the farthest any light has traveled. Anything farther away than
those hydrogen atoms has never been visible to us because it is
too far away. But when they emitted the cosmic background,
those hydrogen atoms were only 42 million light-years away.
The expansion of space between the hydrogen atoms and us
has given the light a much, much larger distance to travel to
reach us. The hydrogen atoms are now much farther away --
47 billion light years.

We can see vast numbers of distant galaxies that were more
than 42 million light-years away when they emitted the light
we now see from them, but they emitted that light more recently
and were closer to us than the hydrogen atoms which had earlier
emitted the background radiation, so their light has traveled less
than 13.7 billion light-years to reach us, and they are now less
than 47 billion light-years away.

None of that answers the original question about why we think
the Universe is 13.7 billion years old, which is too big a topic for
me to go into, and can be found on Ned Wright's web pages
and lots of other places, anyway.

-- Jeff, in Minneapolis

tnjrp
2011-Aug-19, 12:24 PM
I think it is reasonable to say that a distance of 13.7 billion
light-years (the figure I generally use) is the farthest we can
see. It would also be reasonable to say that the farthest we
can see is much less than 13.7 billion light-years.
Well, this is probably something that can lead to a lot of eventually completely pointless semantic wrangling. While it can certainly be reasoned that we in fact only see to a distance of ca. 13.7 billion LY (or less), I find flatly statting this to be so to be merely confusing to a layperson. An opinion based on what I think is fairly well explained in the Wikipedia and also on Ned Wright page and elsewhere.

E.g. http://en.wikipedia.org/wiki/Observable_universe#Size

tommac
2011-Aug-19, 03:41 PM
We, the science community and those interested in this BIG question are adamant and sure that by direct observation,

and the study of information attained that the Universe as a whole is expanding at a ever increasing rate.

That only gravity bound objects are the exception to this fact.

That would not be in conductance with the workings of a Black Hole. Therefore we are not in or part there of one.

Why not?

Doesnt space expand as one falls through an EH? What is the maximum amount that space can expand? Or would that only be in the direction away from the singularity?

Tensor
2011-Aug-19, 09:31 PM
Why not?

Doesnt space expand as one falls through an EH? What is the maximum amount that space can expand? Or would that only be in the direction away from the singularity?

The two singularities do not act the same. It's really that simple.

astromark
2011-Aug-19, 10:46 PM
Mark looks over his shoulder for 'Other' singularity... NO. Tommac, no.

The whole of the known Universe is NOT a Black Hole.

tommac
2011-Aug-22, 01:09 PM
Mark looks over his shoulder for 'Other' singularity... NO. Tommac, no.

The whole of the known Universe is NOT a Black Hole.



but you made a statement:

That would not be in conductance with the workings of a Black Hole.

That is what I am questioning. Why wouldnt it be? I am not making a statement. I am questioning your statement. Could you clarify on this point?

Strange
2011-Aug-22, 01:16 PM
but you made a statement:


That is what I am questioning. Why wouldnt it be? I am not making a statement. I am questioning your statement. Could you clarify on this point?

They are different things. Why would you consider them the same? Because they both have mathematical singularities associated with them? But a singularity isn't a "thing"; and one type (or cause) of singularity doesn't have any necessary connection to another. More specifically:


There are several subtle mathematical reasons for concluding that the universe is not a black hole (nor a white hole). Quickly, objects within General Relativity have what are called world lines. These lines describe how the objects moves through spacetime. In a black hole, the singularity is where all world lines end. In the Big Bang singularity, it's where all world lines begin. Another way of saying this is that a Black Hole singularity is always in the future, the Big Bang singularity is always in the past. This site (http://www.weburbia.com/physics/universe.html) may answer some of your questions more fully.

tommac
2011-Aug-22, 04:49 PM
I am not considering anything ... I am asking astromark to clarify his statement.


They are different things. Why would you consider them the same? Because they both have mathematical singularities associated with them? But a singularity isn't a "thing"; and one type (or cause) of singularity doesn't have any necessary connection to another. More specifically:

tommac
2011-Aug-22, 04:50 PM
This really has nothing to do with Astromarks comment.



They are different things. Why would you consider them the same? Because they both have mathematical singularities associated with them? But a singularity isn't a "thing"; and one type (or cause) of singularity doesn't have any necessary connection to another. More specifically:

tommac
2011-Aug-22, 04:54 PM
To clarify what I am asking Astromark is based on his statement:


and the study of information attained that the Universe as a whole is expanding at a ever increasing rate.That only gravity bound objects are the exception to this fact. That would not be in conductance with the workings of a Black Hole.

It is only about this particular statement that I am questioning. For me it seems like a jump in logic. I would like to see the holes filled in for this logic. Note ... I am not proposing that this is not true ... but I would like to see particularly HOW he has come to the conclusion of :


That would not be in conductance with the workings of a Black Hole

Based on:


and the study of information attained that the Universe as a whole is expanding at a ever increasing rate.That only gravity bound objects are the exception to this fact.

I am sure he is right ... but just am interested in the derivation.


but you made a statement:


That is what I am questioning. Why wouldnt it be? I am not making a statement. I am questioning your statement. Could you clarify on this point?

ShinAce
2011-Aug-22, 06:32 PM
Slow down. You won't get an answer to one question if you ask others as well.

Space is expanding. The expansion really appears to be accelerating. Galaxies themselves are held together by their own gravity and resist being exploded by the expansion. This model does not look like a black hole.

It is in fact you, Tommac, that said that black holes expand space. This is the only statement that needs explaining. If I say that space is falling into a black hole instead of being stretched from outside to inside the black hole, who's going to correct me?

We can not take simple language, like "space is expanding" and "black holes ~expand~ space" to conclude that black holes are responsible for the expansion of the universe.

Like many have said, a black hole is a singularity in the future of worldlines. I want to live so I prefer a singularity in my past worldlines.

Singularity in the past = you can live forever

Singularity in the future = you can only live for so long before you meet your singularity

tommac
2011-Aug-22, 07:03 PM
Again ... I am just trying to figure out Astromark's point. Not to pose anything.

I ask for clarrification on your point now:
You state:

This model does not look like a black hole.

Can you show how it is different? If it doesnt look like a black hole then what are the differences?






Slow down. You won't get an answer to one question if you ask others as well.



Space is expanding. The expansion really appears to be accelerating. Galaxies themselves are held together by their own gravity and resist being exploded by the expansion. This model does not look like a black hole.

It is in fact you, Tommac, that said that black holes expand space. This is the only statement that needs explaining. If I say that space is falling into a black hole instead of being stretched from outside to inside the black hole, who's going to correct me?

We can not take simple language, like "space is expanding" and "black holes ~expand~ space" to conclude that black holes are responsible for the expansion of the universe.

Like many have said, a black hole is a singularity in the future of worldlines. I want to live so I prefer a singularity in my past worldlines.

Singularity in the past = you can live forever

Singularity in the future = you can only live for so long before you meet your singularity

astromark
2011-Aug-22, 08:11 PM
Oh Tommac you ask of me too much... please take a breath...

It is enough for me to hold the mainstream view. That I expressed it in a way you find issue with bothers me...

'The Universe is expanding.' That statement is true and direct observation can support that., and has.

It has been the mainstream view for a number of reasons and for years is the model that best fits the facts that we observe.

If you can find a way to explain what I have said that you find confusing..? I have looked carefully at what I said.

and would not change it.

Its true that a black hole is all consuming.

That the expansion of space time does NOT contradict the model we observe as true.

I can not equate the expansion of the Universe with the 'Shrinking to a event horizon' of a Black Hole.

How or why do you alone not see this...? or that you do and just want for a argument..

Ask of me a question and I shall give it my attention.. Mark.

tommac
2011-Aug-22, 08:43 PM
I think the way that you word this is more correct.

When you state:

That would not be in conductance with the workings of a Black Hole.

as a fact ... is different than stating that you dont see a correlation. I am more accepting of this second explaination.







Oh Tommac you ask of me too much... please take a breath...

It is enough for me to hold the mainstream view. That I expressed it in a way you find issue with bothers me...

'The Universe is expanding.' That statement is true and direct observation can support that., and has.

It has been the mainstream view for a number of reasons and for years is the model that best fits the facts that we observe.

If you can find a way to explain what I have said that you find confusing..? I have looked carefully at what I said.

and would not change it.

Its true that a black hole is all consuming.

That the expansion of space time does NOT contradict the model we observe as true.

I can not equate the expansion of the Universe with the 'Shrinking to a event horizon' of a Black Hole.

How or why do you alone not see this...? or that you do and just want for a argument..

Ask of me a question and I shall give it my attention.. Mark.

tommac
2011-Aug-22, 08:45 PM
Also what do you mean by shrinking to an event horizon?





Oh Tommac you ask of me too much... please take a breath...

It is enough for me to hold the mainstream view. That I expressed it in a way you find issue with bothers me...

'The Universe is expanding.' That statement is true and direct observation can support that., and has.

It has been the mainstream view for a number of reasons and for years is the model that best fits the facts that we observe.

If you can find a way to explain what I have said that you find confusing..? I have looked carefully at what I said.

and would not change it.

Its true that a black hole is all consuming.

That the expansion of space time does NOT contradict the model we observe as true.

I can not equate the expansion of the Universe with the 'Shrinking to a event horizon' of a Black Hole.

How or why do you alone not see this...? or that you do and just want for a argument..

Ask of me a question and I shall give it my attention.. Mark.

ShinAce
2011-Aug-22, 08:45 PM
I can not clarify any better than Tensor already has. Nor do i want to entertain a discussion as to why i don't live in a black hole.

WayneFrancis
2011-Aug-23, 02:57 AM
hi,
i'm also new,but minus Simore79's bravery which he's going to need by the look of it.i suppose i am looking for a little enlightenment,of which there would seem to be a plentiful supply. so,(gulp),is it possible that we are the other side of a black hole,any huge black hole and i hope i will not be required to explain it's origin because we can't really explain our own origin can we?
i hope no one will object to me bringing the discussion down to my level,for verily it has been said that, 'a fool may ask a wise man a question he cannot answer' and i certainly qualify here.
one thing which has always puzzled me is the certainty with which it is stated that the universe is 13.6 billion years old, this seems to be based on the fact that this is the farthest we can see in light years to the, 'horizen', and this, 'horizen', seems to be to extend in any direction all around us, which in turn seems to suggest that we are the centre of the universe,as this seems to be a little unlikely i wonder if someone could possibly elucidate.
if there is an horizen which we have reached since BB, then surely there must have been a place of origin, shall we call it a,'singularity', does any one have any idea where we might start to look for it?.

Hi mimmermus and welcome to BAUT,
There are a few misunderstandings you have and I'll try to briefly address some of them.

It is very doubtful that we are in a black hole. I wouldn't think that the topology of space would be anything like what we see when we look around the universe.
The age of 13.75 billion years is derived from some complex measurements and various observations and not directly from the z value of the furthest objects. It just happens that we live in a time where the Hubble distance is about the same age of the visible universe. Others here have described this in much better words then I can.

The cosmic horizon is different then a black hole horizon because, depending on the expansion of the universe objects out side of our current cosmic event horizon could come into our cosmic event horizon and back out again. This is a very different trait then the EH of a black hole.

The BB model doesn't extend back to a singularity simply because our understanding of physics breaks down before that point.

astromark
2011-Aug-23, 07:10 AM
"Tommac" I do not except you do not know of what I speak... my choice of words was quite deliberate.

'Shrinking to a event horizon'.. Is what I wanted to say. Because we do not know anything about what might happen inside that. We can and do make speculations based on logic and good science.

In falling mater that is been drawn into a Black Hole is been carried by the space its in... THAT is NOT the action we see in the universe we are part of... IT is expanding... what do you not see ?

Please do not complicate "Minmermus's" good question with others...

astromark
2011-Aug-23, 07:27 AM
We, the science community and those interested in this BIG question are adamant and sure that by direct observation,

and the study of information attained that the Universe as a whole is expanding at a ever increasing rate.

That only gravity bound objects are the exception to this fact.

That would not be in conductance with the workings of a Black Hole. Therefore we are not in or part there of one.

Expanding space time is not apparent in my working modal of a Black Hole.. This subject is different. The observable universe would seem to be expanding... that is the reality I know of...

tommac
2011-Aug-23, 01:49 PM
So by "shrinking to an event horizon" you mean that for the external observer as one get close to the EH they appear to shrink, correct? So what would the external observer to our universe observe?

Also when you say :

This model does not look like a black hole.

Are you saying it does not look like model of something falling into a black hole, but still external to it?



"Tommac" I do not except you do not know of what I speak... my choice of words was quite deliberate.

'Shrinking to a event horizon'.. Is what I wanted to say. Because we do not know anything about what might happen inside that. We can and do make speculations based on logic and good science.

In falling mater that is been drawn into a Black Hole is been carried by the space its in... THAT is NOT the action we see in the universe we are part of... IT is expanding... what do you not see ?

Please do not complicate "Minmermus's" good question with others...

tommac
2011-Aug-23, 01:50 PM
Expanding space time is not apparent in my working modal of a Black Hole.. This subject is different. The observable universe would seem to be expanding... that is the reality I know of...

And for the free faller into the BH? How would their universe appear? Would it be expanding or contracting?

tommac
2011-Aug-23, 01:52 PM
Please do not complicate "Minmermus's" good question with others...

Sorry ... but you made a fairly stong statement and I would also like to understand the basis that this statement was made. If it is to help Minmermus out in his understanding of the answer then lets shed just a little bit a of light on the statement that you are making.

tommac
2011-Aug-23, 01:57 PM
This is a very different trait then the EH of a black hole.

Are you talking about something that is inside of the EH looking out at the EH? I believe that is what mimnermus is asking when he states:

is it possible that we are the other side of a black hole

tommac
2011-Aug-23, 01:59 PM
Well then why are you posting in a thread that is titled:
[are we in a black hole?]


I can not clarify any better than Tensor already has. Nor do i want to entertain a discussion as to why i don't live in a black hole.

Swift
2011-Aug-23, 02:08 PM
Well then why are you posting in a thread that is titled:
[are we in a black hole?]
And why are you telling other members what to post? If you think another member's post is inappropriate, you Report it, you don't question it. But you knew that, or should have.

tommac
2011-Aug-23, 02:08 PM
hi,
i'm also new,but minus Simore79's bravery which he's going to need by the look of it.i suppose i am looking for a little enlightenment,of which there would seem to be a plentiful supply. so,(gulp),is it possible that we are the other side of a black hole,any huge black hole and i hope i will not be required to explain it's origin because we can't really explain our own origin can we?

The mainstream answer is no we are not in a black hole. However you will find articles such as:
http://news.nationalgeographic.com/news/2010/04/100409-black-holes-alternate-universe-multiverse-einstein-wormholes/
or
http://members.cox.net/jhaldenwang/black_hole.htm






i hope no one will object to me bringing the discussion down to my level,for verily it has been said that, 'a fool may ask a wise man a question he cannot answer' and i certainly qualify here.
one thing which has always puzzled me is the certainty with which it is stated that the universe is 13.6 billion years old, this seems to be based on the fact that this is the farthest we can see in light years to the, 'horizen', and this, 'horizen', seems to be to extend in any direction all around us, which in turn seems to suggest that we are the centre of the universe,as this seems to be a little unlikely i wonder if someone could possibly elucidate.
if there is an horizen which we have reached since BB, then surely there must have been a place of origin, shall we call it a,'singularity', does any one have any idea where we might start to look for it?.

I believe the mainstream answer to this point is that the singularity was everywhere. There is no direction to the expansion ... just the metric/scale factor is changing. Therefor the singularity is now everywhere ... there is no center or place of origin.

tommac
2011-Aug-23, 02:22 PM
I would also like to point out that there is a difference between:
Falling into a Black Hole and observing the EH
and
Being Inside a black hole and looking out at the EH.

It seems that many of these posts are discussing the EH of a black hole in comparison to event horizon past our visible universe. To me these would seem to be arguments that we are not "Falling into a black hole" rather than arguments that we are inside a black hole looking out.

While i have no opinion on this I would also like to see the reasons how it would be so different?

WayneFrancis
2011-Aug-23, 04:24 PM
And for the free faller into the BH? How would their universe appear? Would it be expanding or contracting?

I have shown you before that for one it would not be symmetric in all directions. The expansion of the universe is symmetric.

WayneFrancis
2011-Aug-23, 04:35 PM
Are you talking about something that is inside of the EH looking out at the EH? I believe that is what mimnermus is asking when he states:

You can't look out at the EH within a black hole. Once you are past the EH all directions lead to the singularity and away from the EH.

With a cosmological event horizon the horizon changes with time and is only a function of time in a static universe. The EH of a black hole is not a function of time. In a universe that has expansion that varies in rate object can freely pass the EH in both direction freely based on both time and the rate of expansion.

tommac
2011-Aug-23, 07:08 PM
I have shown you before that for one it would not be symmetric in all directions. The expansion of the universe is symmetric.

Yes, I remembered that we agreed to disagree. but it would appear to be expanding ... at least along the axis of acceleration ... correct?
This point is far different than :

'Shrinking to a event horizon'

Again I am not taking any side of if it is or isnt ... but just want to make sure that the arguments from either side are argued correctly for
mimnermus' sake.

tommac
2011-Aug-23, 07:12 PM
You can't look out at the EH within a black hole.

Why would it be any different? As I am crossing the EH as a free faller are you saying that immediately I cant see anything on the outside? Can you please show your proof of this? Now I understand that photons cant leave ... but photons can enter and will travel at the speed of light from outside the EH to my eye.
I think it is redundant to state that the photon will have to be inside the EH ... as my eye is inside of the EH. But what I am observing is outside the EH.

tommac
2011-Aug-23, 07:15 PM
With a cosmological event horizon the horizon changes with time and is only a function of time in a static universe. The EH of a black hole is not a function of time. In a universe that has expansion that varies in rate object can freely pass the EH in both direction freely based on both time and the rate of expansion. Can you please show an example?

Also again ... it seems that you are comparing falling into a BH and looking at the EH ... not from the inside outward. I assume that when you say the EH of a black hole is not a function of time you are stating that from something that is outside of EH ... which is not what was suggested by anyone on this thread.

astromark
2011-Aug-23, 07:58 PM
'Tommac' It is obvious to me that you do not see things as I do.

That you ask and make statements of understanding that I find confusing.

That a 'new' member asked a question regarding his understanding of what a black hole is ( the OP )

Are we in one ? On the other side of one ? or whatever... I see that most of us are simply attempting to guide the thinking of the questioner.. To learn and gain understanding..

I am NOT attempting to reason with you. Its a task too hard.

You do not seem to take the same meanings from script as the rest of us.. Start a new thread.

Cougar
2011-Aug-23, 08:10 PM
Are we in a black hole?

No, we're not. This topic was brought up a bit over a year ago in a thread titled The Universe Is Not A Black Hole. (http://www.bautforum.com/showthread.php/103516-The-Universe-is-Not-a-Black-Hole?highlight=)

For one thing, you may have noticed that the universe is actually expanding, rather than contracting, as you would expect the interior of a black hole to be.

Jeff Root
2011-Aug-24, 12:05 AM
Although I don't think the Universe is inside a black hole, there
are similarities. General relativity says that the amount of space
in the Universe is increasing as a function of time. GR also says
that the amount of spacetime in a black hole is increasing as a
function of time. The longer the black hole exists, the "deeper"
its gravitational well, and the farther it is to the singularity at the
very center. Here I am only talking about the GR prediction that
the matter in a black hole must collapse forever, not the QM
prediction that such an unending collapse is meaningless.

-- Jeff, in Minneapolis

WayneFrancis
2011-Aug-24, 01:34 AM
Yes, I remembered that we agreed to disagree.


I remember detailing the maths that showed it the expansion rate would be far from symmetrical and that perpendicular to the direction of motion it would actually be the opposite of what we see and you claiming that at that scale you wouldn't notice the difference ignoring all the maths that was presented to you.



but it would appear to be expanding ... at least along the axis of acceleration ... correct?


And that is just one fatal flaw. Forget that what you see perpendicular to the the direction of motion is opposite to what you see in the direction of motion and let us just look at what you've said. What you see in the direction of motion would not be symmetrical with the opposite direction. What we see in cosmological expansion is completely symmetrical in all directions. It isn't that the differences we are looking at are beyond our ability to measure and could be hidden in the error bars. It is that our observations don't match the most likely models of what happens when something would be falling into/already fallen into a black hole. And if you want to say "well maybe our models are wrong" then you have to come up with a reason why all the mainstream models and observations would disagree with us falling into some super huge cosmic black hole and how any model that shoe horn the observations to fit into "falling into a black hole" is actually more likely then what we have now or the argument is no better then saying "invisible pink winged unicorns are responsible". Sure that might be true but there is absolutely zero evidence to indicate that.




This point is far different than :

Again I am not taking any side of if it is or isnt ... but just want to make sure that the arguments from either side are argued correctly for
mimnermus' sake.

The problem is your repeated questions on top of answers that explain that what we observe is not what we'd expect to see if we where inside a black hole can make a lay person think "Hey, I don't get the details of this argument but tommac's repeated question must be because they've all forgot something and the idea of us being inside a black hole must be valid"

It is only valid if things are drastically different from what we'd expect if we where either falling into a black hole or already passed said black hole's EH.

It isn't much different then having a child ask "Why is the sky blue? Is it because the oceans are blue?" and someone telling the child "No the sky is blue because the blue light from the sun is scattered by the air making it look blue." and the you keep coming up with "But wouldn't the blue ocean have an effect of making the sky look blue because ...." and each time it is explained why the sky is blue you make it sound like we didn't understand the question and are missing something.

That is how it comes across in my mind.

Jeff Root
2011-Aug-24, 01:49 AM
I think Tom's questions are pretty good. He repeats them a lot,
but it is usually for a good reason -- there is frequently ambiguity
or some other problem with the reply.

-- Jeff, in Minneapolis

WayneFrancis
2011-Aug-24, 01:49 AM
Why would it be any different? As I am crossing the EH as a free faller are you saying that immediately I cant see anything on the outside? Can you please show your proof of this? Now I understand that photons cant leave ... but photons can enter and will travel at the speed of light from outside the EH to my eye.
I think it is redundant to state that the photon will have to be inside the EH ... as my eye is inside of the EH. But what I am observing is outside the EH.

That is not what I said. What I said is that when you are falling into a black hole you won't have any object appear to you, after you passed the EH, that you didn't already see. With a cosmological event horizon it is possible that you could see new objects appear.

The EH for a static universe is completely a function of time and for a universe that is expanding, contracting or both then it is a function of time and the expanding\contracting. For a black hole the EH is a function of the mass of the BH.

!=

They are 2 different things even tho they can have some similar properties there are differences between them.

It is like apples and oranges are both fruit but the skin of an apple is different then the skin of an orange and I can't squeeze and apple skin over an open flame and see little jets of fire.

The EH of a black hole is different then the EH of our Hubble sphere.

Tensor
2011-Aug-24, 02:15 AM
Can you please show an example?

If Wayne doesn't mind me jumping in here. Try here (http://arxiv.org/pdf/math/0603190v4). From your recent posts, feel free to point out exactly what you don't like about this explanation.


Again I am not taking any side of if it is or isnt ... but just want to make sure that the arguments from either side are argued correctly for
mimnermus' sake.

There is no either side of this argument, there is only one side. The universe is not a black hole. Feel free to point out exactly where in that paper you think there is another side.

WayneFrancis
2011-Aug-24, 02:53 AM
Can you please show an example?


Sigh, why do I get the feeling I'm going to spend my time showing proofs to this to have you hand wave it away. So for the lurkers.

In a universe like ours what we can see is dependent on 2 factors. The time an event occurred and the accumulated amount of expansion between the point where the the event happened and the point you are observing from.

No expansion - An event happens at T1 and is a distance of n away where n is a distance in some unit of c then the observer will see at a distance of n away = T1 + n

Expansion - the event horizon will be the a comoving distance where an event will never reach us and is found by the formula
d_{e}(t_{o}) = a(t_{0})\int_{t_{0}}^{t_{max}}\frac{dt'}{a(t')}

Basically there are points in space that due to the current scale factor we will not be able to observe because the amount of space being created between the event and the observer is at a rate that is higher then c. But if the scale factor changes and the rate of expansion slows down enough in the future then those events will be within our cosmic event horizon and we just have to wait. We don't expect the rate of expansion to slow at this point but there is nothing in our models to say it can't.

Compare this to the EH of a black hole. Once some event happens inside the EH there is NOTHING an external observer can do to see that event. Even if they travelled as fast as they could through the EH they'll never catch up to a point where they would see that event.

So in a sense the cosmic event horizon is fuzzy and the factors that make it can change in such a way events that where beyond the EH are no longer beyond the EH while in a black hole, even on the inside of the EH, there are events that you will never see because they happened to long after you passed the EH. IE you'll hit the singularity before they can catch up to you and this is strictly a function of the size of the black hole when you passed through the EH.






Also again ... it seems that you are comparing falling into a BH and looking at the EH ... not from the inside outward.



What I'm describing is what a free faller is expected to see falling into a black hole and what they would observe after passing the EH of the black hole.



I assume that when you say the EH of a black hole is not a function of time you are stating that from something that is outside of EH ... which is not what was suggested by anyone on this thread.

What? Please tell me how after you've fallen past the EH of a black hole how you would say that the EH is then a function of time and not the BH's mass?

Doesn't matter if you are inside or outside the EH of the BL. Once inside the EH of a black hole there is a EH that follows you right behind you. Now I'm not saying that you can't see something that appears to be behind you. What I'm saying is you can't look at the EH. Inside the EH there is no direction that points anywhere but the singularity. You still have a past future light cone where you can receive information that was further out then you but you can't look in the direction of the EH because there isn't one. This though is just confusing the issue more.

There are a few threads that describe very nicely what actually happens with the light cones of a free falling observer as they fall past the EH of a black hole.

WayneFrancis
2011-Aug-24, 02:58 AM
If Wayne doesn't mind me jumping in here. Try here (http://arxiv.org/pdf/math/0603190v4). From your recent posts, feel free to point out exactly what you don't like about this explanation.



There is no either side of this argument, there is only one side. The universe is not a black hole. Feel free to point out exactly where in that paper you think there is another side.

Thanks, I tried to provide an examples but not completely happy with my explanations.

This is a good point. Its much like a creationist saying "tell both sides to the theory of evolution" trying to make believe that there is doubt about the validity of common descent. In both topics there is 2 sides. One is the current models science puts forth and one is from the science deniers that ignore the observations and the conclusions you can reach from those observations.

WayneFrancis
2011-Aug-24, 03:06 AM
Although I don't think the Universe is inside a black hole, there
are similarities. General relativity says that the amount of space
in the Universe is increasing as a function of time. GR also says
that the amount of spacetime in a black hole is increasing as a
function of time. The longer the black hole exists, the "deeper"
its gravitational well, and the farther it is to the singularity at the
very center. Here I am only talking about the GR prediction that
the matter in a black hole must collapse forever, not the QM
prediction that such an unending collapse is meaningless.

-- Jeff, in Minneapolis

But that's about the same as saying apples and oranges are the same thing because they are both fruit.
Eat an apple skin and all then do the same to an orange and tell me they are the same thing. I'm not claiming
that there isn't a change in space when you fall into a black hole and when you look at cosmic expansion.
I'm claiming that the changes in space/time are very different then the changes in space that is
happening with cosmic inflation.

Jeff Root
2011-Aug-24, 05:07 AM
But that's about the same as saying apples and oranges are the
same thing because they are both fruit.
Is it "about the same"? No, it isn't. I didn't say anything is
"the same thing". I said "there are similarities".



I'm claiming that the changes in space/time are very different
then the changes in space that is happening with cosmic inflation.
And Tom is trying to find out what those differences are, so he
can decide for himself if the differences are as big as you claim.

-- Jeff, in Minneapolis

tommac
2011-Aug-24, 12:51 PM
I remember detailing the maths that showed it the expansion rate would be far from symmetrical and that perpendicular to the direction of motion it would actually be the opposite of what we see and you claiming that at that scale you wouldn't notice the difference ignoring all the maths that was presented to you.

And I believe I showed you how it can be manipulated in a way where it would work. I any case this is totally off topic for this thread. If you want to revisit this either please ask for that thread to be reopened or start a new thread at httphttp://www.againstthemainstream.com (http://www.spacetimeandtheuniverse.com) and we can finish that discussion.




And that is just one fatal flaw. Forget that what you see perpendicular to the the direction of motion is opposite to what you see in the direction of motion and let us just look at what you've said.


It is not a flaw ... it was intended as a simplification to question a statement that was made. Someone ( I think astromark ) stated that


'Shrinking to a event horizon'

This was to question if his statement is indeed true and if it is ( or isnt ) to clarify it for the original poster.
Personally I dont think his question is as straight forward as people on here are making it out to be ... There seem to be answers but lets delve a little bit into what is behind the replies.










It is only valid if things are drastically different from what we'd expect if we where either falling into a black hole or already passed said black hole's EH.


Is it ... you use the word "drastically" however it seems that the only difference you pose is that the expansion of space is congruent in all directions where falling towards a gravitational source is not. ( something that we can debate on a different thread ) In any case, at minimum, I wouldnt call that drastic.

tommac
2011-Aug-24, 12:54 PM
That is not what I said. What I said is that when you are falling into a black hole you won't have any object appear to you, after you passed the EH, that you didn't already see. With a cosmological event horizon it is possible that you could see new objects appear. .

Guess I am still missing the point ... can you please explain how that is any different from me watching stuff fall through the EH from the inside?

And BTW this was your EXACT quote:

You can't look out at the EH within a black hole.

tommac
2011-Aug-24, 12:56 PM
The EH of a black hole is different then the EH of our Hubble sphere.

Why do you keep stating this ... I dont think anyone is stating anything else.

tommac
2011-Aug-24, 12:58 PM
For one thing, you may have noticed that the universe is actually expanding, rather than contracting, as you would expect the interior of a black hole to be.

Why would we think it would be contracting? Would it be contracting? I would think that looking out from the interior of a BH ( from inside the EH ) or even falling in that space would be expanding not contracting.

tommac
2011-Aug-24, 01:00 PM
Its much like a creationist saying "tell both sides to the theory of evolution" trying to make believe that there is doubt about the validity of common descent. In both topics there is 2 sides. One is the current models science puts forth and one is from the science deniers that ignore the observations and the conclusions you can reach from those observations.

Hand wave?

tommac
2011-Aug-24, 01:09 PM
Basically there are points in space that due to the current scale factor we will not be able to observe because the amount of space being created between the event and the observer is at a rate that is higher then c. But if the scale factor changes and the rate of expansion slows down enough in the future then those events will be within our cosmic event horizon and we just have to wait. We don't expect the rate of expansion to slow at this point but there is nothing in our models to say it can't.

Compare this to the EH of a black hole. Once some event happens inside the EH there is NOTHING an external observer can do to see that event. Even if they travelled as fast as they could through the EH they'll never catch up to a point where they would see that event.



OK a few things. 1) again you are talking about an external observer trying to look into an EH. That is wrong and off topic. It is NOT what is being discussed.
2) What would make you think that the scale factor is going to change? How would that be different from say a BH evaporating?

Cougar
2011-Aug-24, 01:25 PM
For one thing, you may have noticed that the universe is actually expanding, rather than contracting, as you would expect the interior of a black hole to be.Why would we think it would be contracting?

Uh, gravity. Black holes are not amusement parks for your mind. They are objects with extremely strong gravity, which pulls everything toward their centers. Try to keep up.

tommac
2011-Aug-24, 01:30 PM
Doesn't matter if you are inside or outside the EH of the BL. Once inside the EH of a black hole there is a EH that follows you right behind you.

Example please ... never heard of this EH that follows the free faller from behind. Is there a name for this EH that follows the free faller in?



Now I'm not saying that you can't see something that appears to be behind you.


And I am saying you can. Say we have a space ship and we are dropping prisoners into the EH from a safe distance. Each one has a flash light. We drop the prisoners at an arbitrary rate ... As the first prisoner passes the EH ... he will continue to see the light from all of the other flashlights ( until space between them is expanding at a rate of > 2c ???) ( not sure if it is c or 2c due to ant and a rope. )




What I'm saying is you can't look at the EH. Inside the EH there is no direction that points anywhere but the singularity. You still have a past future light cone where you can receive information that was further out then you but you can't look in the direction of the EH because there isn't one. This though is just confusing the issue more.


Again I disagree here. There are infinite directions inside the EH ... all of which eventually lead to the singularity. But there are still infinite directions .... some of those directions are back towards to the EH. What I am saying here is that I can look in the direction of the EH even though space is curved.

Stuff ( say photons of light ) can flow from outside of the EH and I can look at it. Can my eye travel outside the EH ... obviously no. But the same way that I can look up and see a distant star from here on earth ... I can look out from inside the EH and see light (possibly even from the same distant star ).

tommac
2011-Aug-24, 01:32 PM
Uh, gravity. Black holes are not amusement parks for your mind. They are objects with extremely strong gravity, which pulls everything toward their centers. Try to keep up. I agree with these statements ... however space-time expands not contracts, right?

Strange
2011-Aug-24, 01:41 PM
I agree with these statements ... however space-time expands not contracts, right?

Friedman-Robertson-Walker (FRW) spacetime expands, but one of the requirements is that it is of uniform density (homogeneous
and isotropic). This is not true of a black hole. So if you are claiming that spacetime expands in a black hole, then no.

tommac
2011-Aug-24, 01:53 PM
Huh?

So there are 3 option:

1) spacetime expands
2) spacetime niether expnds or contracts
3) spacetime contracts

I would think that there definitely would be some contraction of expansion ... so I am ruling #2 out ... although not sure why.
so we are left with #1 and #3

if we assume that spacetime contracts ... then the observer at the EH would see the entire external universe as a singularity. During his fall he would see the all the stars compress into a point ... and the observer would see that everyone elses clocks slow down to a halt. All light would be severely red shifted

If we assume #1 ( which was always my assumption ) then the universe would appear to expanding in and against the direction or gravity. The observer would see everyones clocks in the universe speed up. All light would be severely blue shifted




Friedman-Robertson-Walker (FRW) spacetime expands, but one of the requirements is that it is of uniform density (homogeneous
and isotropic). This is not true of a black hole. So if you are claiming that spacetime expands in a black hole, then no.

Strange
2011-Aug-24, 01:58 PM
Huh?

Sorry. I didn't follow any of that. Spacetime expands on large (very large) scales because at those scales it can be taken to be uniform. This is not true in the presence of significant matter (i.e. at the scale of galaxy clusters and smaller) which is why the space between and within galaxies is not expanding. I struggle to see what this has to do with the OP though. If we were in a black hole we would be heading rapidly towards the singularity. We are not, ergo ...

tommac
2011-Aug-24, 02:13 PM
This has to do to try to figure out what you mean by statements like:


If we were in a black hole we would be heading rapidly towards the singularity. We are not, ergo

while we all agree with you we are looking for a bit more detail in these sort of statements. So lets start with ... how can this be ruled out? How do we know we are not?

And we are also discussing it because it seems that many of the arguments which are based on looking into an EH, which no one is claiming ... that space does not expand as one falls into an EH ... which is not true, that 'Shrinking to a event horizon' which I am not sure what it means ... that you cant see stuff external to EH from inside the EH ... which is not true.

Nobody is claiming that the universe is inside of a black hole ... we are asking these question to figure out which are valid arguments as to why it is not.

I am not satisfied with accepting blindly that it is not based on a bunch of handwaving, distractions, and false or misguided statements.

So maybe we can start over ...

What are the strongest arguements that we are not in a black hole and what are the main differences of an expanding universe and looking from the inside of a BH outwards?

wayne has a decent argument ... which is that space does not expand equally in all directions. So we can start with that as the main ( and only valid ) argument that I have seen so far in this thread ... lets add a few more to help answer the Original Question.


Sorry. I didn't follow any of that. Spacetime expands on large (very large) scales because at those scales it can be taken to be uniform. This is not true in the presence of significant matter (i.e. at the scale of galaxy clusters and smaller) which is why the space between and within galaxies is not expanding. I struggle to see what this has to do with the OP though. If we were in a black hole we would be heading rapidly towards the singularity. We are not, ergo ...

tommac
2011-Aug-24, 02:17 PM
In SR - GR ... does spacetime expand and contract? Or are you claiming it doesnt?
And if so do you feel that space time expands or contracts from the point of view of a freefaller into a black hole?


Sorry. I didn't follow any of that. Spacetime expands on large (very large) scales because at those scales it can be taken to be uniform. This is not true in the presence of significant matter (i.e. at the scale of galaxy clusters and smaller) which is why the space between and within galaxies is not expanding. I struggle to see what this has to do with the OP though. If we were in a black hole we would be heading rapidly towards the singularity. We are not, ergo ...

Strange
2011-Aug-24, 02:27 PM
Nobody is claiming that the universe is inside of a black hole ... we are asking these question to figure out which are valid arguments as to why it is not.

Isotropy is one. The fact that the big-bang singularity is in the past not the future (see post #3) is another. The fact that the cosmological event horizon is different from a black-hole horizon is a third (post #46). I think there might have been more but how many do you need to falsify the idea.

Strange
2011-Aug-24, 02:32 PM
In SR - GR ... does spacetime expand and contract? Or are you claiming it doesnt?

I said, "spacetime expands on large (very large) scales because at those scales it can be taken to be uniform" (actually, that should just be "space"). It could contract if the density were different, I believe.


And if so do you feel that space time expands or contracts from the point of view of a freefaller into a black hole?

I can't answer that because I can't do the math.

tommac
2011-Aug-24, 02:46 PM
The fact that the cosmological event horizon is different from a black-hole horizon is a third (post #46).

This is again going back to the questions that we are trying to answer .... To ask the question again ... HOW is the cosmological event horizon different from looking out to the EH from inside of the EH a black hole? It seems that the way you pose this statement is from an external observer looking into a BHs EH. Which is faulty logic.

tommac
2011-Aug-24, 02:48 PM
I can't answer that because I can't do the math.
Although the math would be nice ...
It is clear that spacetme expands due to the blue shift.

tommac
2011-Aug-24, 02:49 PM
The fact that the big-bang singularity is in the past not the future (see post #3) is another. The BH's EH is in the past also ( for something that has already passed it.)

Strange
2011-Aug-24, 02:57 PM
This is again going back to the questions that we are trying to answer .... To ask the question again ... HOW is the cosmological event horizon different from looking out to the EH from inside of the EH a black hole? It seems that the way you pose this statement is from an external observer looking into a BHs EH. Which is faulty logic.

It is nothing to do with "looking in" or "looking out". Reread post #46.

Strange
2011-Aug-24, 02:57 PM
The BH's EH is in the past also ( for something that has already passed it.)

"The fact that the big-bang singularity is in the past not the future (see post #3) is another."

tommac
2011-Aug-24, 03:01 PM
It is nothing to do with "looking in" or "looking out". Reread post #46.

Reread ... it has everything to do with being an external observer or not. Remember we are not looking at the EH of the BH as a true horizon ... we can see past the horizon ... we can see distant stars ... this is very different than what is being explained in post 46 and has already been addressed in replies to that post.

tommac
2011-Aug-24, 03:01 PM
"The fact that the big-bang singularity is in the past not the future (see post #3) is another."

What does this have to do with ANYTHING?

Strange
2011-Aug-24, 03:07 PM
Reread ... it has everything to do with being an external observer or not.

No. It is to do with the fact that, if things change, stuff can move into and out of the the cosmological event horizon. Unlike a black-hole horizon.

Strange
2011-Aug-24, 03:09 PM
What does this have to do with ANYTHING?

It was the first, and rather fundamental, difference raised between a black hole and the universe. If you are in a black hole, the singularity is in the future. The big-bang singularity is in the past. Ergo, we are not in a black hole.

tommac
2011-Aug-24, 03:42 PM
It was the first, and rather fundamental, difference raised between a black hole and the universe. If you are in a black hole, the singularity is in the future. The big-bang singularity is in the past. Ergo, we are not in a black hole.

That logic sounds faulty. Just because there was a singularity in the past and a singularity in the future which are not the same doesnt mean that there cant be both. Just because A does not equal B does not mean that C does not equal C.

tommac
2011-Aug-24, 03:43 PM
No. It is to do with the fact that, if things change, stuff can move into and out of the the cosmological event horizon. Unlike a black-hole horizon.

Can you please provide an example of how the scale factor can change? Also which Black Hole horizon are you talking about? The EH as observed externally?

ShinAce
2011-Aug-24, 04:42 PM
http://jila.colorado.edu/~ajsh/insidebh/schw.html

Thats an animation of what the milky way might appear like as you fall into a black hole. This is an attempt at the view 'out'.

You can look for Hubble images yourself. I see no similarity. Indeed, visually they are opposite. Our universe shows no sign of a singularity in th future.

tommac
2011-Aug-24, 05:49 PM
I dont see the view 'out' only the view 'in' .... which video are you referring to?

what signs would you expect for the singularity in the future?


http://jila.colorado.edu/~ajsh/insidebh/schw.html

Thats an animation of what the milky way might appear like as you fall into a black hole. This is an attempt at the view 'out'.

You can look for Hubble images yourself. I see no similarity. Indeed, visually they are opposite. Our universe shows no sign of a singularity in th future.

Strange
2011-Aug-24, 06:15 PM
Can you please provide an example of how the scale factor can change?

It is not about the scale factor changing; it is always changing. It is about rate of change. Currently, there are objects which are being "pushed" beyond the event horizon and disappearing from view. When the rate of change was slower (remember it was decelerating once) then object would have come into view through the even horizon.

A block-hole's event horizon, on the other hand, is a one-way street.


Also which Black Hole horizon are you talking about? The EH as observed externally?

The event horizon at the Schwarzschild radius. Is there another.

tommac
2011-Aug-24, 06:25 PM
The event horizon at the Schwarzschild radius. Is there another.

Then it is easy to see the light emmited from objects behind the Schwarzschild radius.

Even from distant galaxies.

Strange
2011-Aug-24, 06:34 PM
Then it is easy to see the light emmited from objects behind the Schwarzschild radius.

Even from distant galaxies.

Er, yeah. But it only goes one way.

I just noticed that the Wayne mentioned another key difference between the event horizon's: the event horizon of black hole is determined by mass; the event horizon of the universe is time-dependent.

So, in summary, the event horizons are completely different and the singularities are completely different; one is isotropic and the other isn't. Not so much apples and oranges, more apples and aardvarks.

tommac
2011-Aug-24, 06:55 PM
I just noticed that the Wayne mentioned another key difference between the event horizon's: the event horizon of black hole is determined by mass; the event horizon of the universe is time-dependent..

Again ... you are confusing looking at a black hole from an external viewpoint. From inside the expansion of space is time dependant. ( the more time you freefall the more the universe will appear to expand ). As a freefaller your time is set space becomes timelike.

What we need to be careful of is not referrring to the BH from how we understand it from an external viewpoint unless we have a way to also look at the universe from an external point of view.

tommac
2011-Aug-24, 07:01 PM
It doesnt seem like we will progress much further in this discussion ...
But you can see that it is not a straight forward answer. The mainstream answer is no we are not in a black hole as it does not fit into the current mainstream model of how we model/envision the universe. Does that mean that the answer is an absolute no ? ... you decide.

Strange
2011-Aug-24, 07:06 PM
Again ... you are confusing looking at a black hole from an external viewpoint. From inside the expansion of space is time dependant. ( the more time you freefall the more the universe will appear to expand ).

You seem to be confusing things. As for example, in this instance, (a) the nature of the black hole's event horizon (which is purely dependent on its mass and nothing to do with being inside, outside, falling in or moving away) (b) how the external universe might appear to someone in (or falling in) and (c) expansion of the universe which has (as far as I can see) nothing to do with the previous two.

Cougar
2011-Aug-24, 07:32 PM
So there are 3 option...

Wrong. Let me restate what Strange said, which you apparently ignored:


Friedman-Robertson-Walker (FRW) spacetime expands, but one of the requirements is that it is of uniform density (homogeneous and isotropic). This is not true of a black hole.

You are trying to put a global concept into your own local viewpoint. It ain't gonna fit.

ShinAce
2011-Aug-24, 08:02 PM
A singularity in your future would be your cause of death.

tommac
2011-Aug-24, 08:15 PM
I didnt ignore it ... I asked a question then.

Are you saying that there is no other way for spacetime to expand?

Does spacetime expand or contract per SR or GR?



Wrong. Let me restate what Strange said, which you apparently ignored:


Friedman-Robertson-Walker (FRW) spacetime expands, but one of the requirements is that it is of uniform density (homogeneous and isotropic). This is not true of a black hole.

You are trying to put a global concept into your own local viewpoint. It ain't gonna fit.

tommac
2011-Aug-24, 08:16 PM
A singularity in your future would be your cause of death.

Point being?

Strange
2011-Aug-24, 08:17 PM
Does spacetime expand or contract per SR or GR?

Yes, it expands or contracts, depending on the density of matter (as I understand it).

tommac
2011-Aug-24, 08:18 PM
The BHs event horizon is not a true horizon when viewed from the inside. For example ... if I was inside I can clearly witness events that are happening outside the EH. It is only an event horizon when you are looking in ... someone outside can not see the events that are happening from inside the EH ... but someone inside CAN see events that have happened outside. a photon can travel from outside of the EH to hit my eye if I am on the inside of the EH ...



You seem to be confusing things. As for example, in this instance, (a) the nature of the black hole's event horizon (which is purely dependent on its mass and nothing to do with being inside, outside, falling in or moving away) (b) how the external universe might appear to someone in (or falling in) and (c) expansion of the universe which has (as far as I can see) nothing to do with the previous two.

tommac
2011-Aug-24, 08:20 PM
Yes, it expands or contracts, depending on the density of matter (as I understand it).

Which is my point. The fact that Friedman-Robertson-Walker (FRW) spacetime expands does not mean that GR can not expand spacetime.

in the case of someone freefalling into a BH GR is expanding space time the deeper into the hole the observer goes.

astromark
2011-Aug-24, 08:30 PM
I do not think your argument 'Tommac' has helped or in any way addressed the OP.. Have a look at that OP

If you want for a argument regarding your understanding of what might or might not be seen from whatever view point you pick..
I have little care for.
THIS thread, THIS question.. is not yours to derail.. and derail it you have..

THE answer to THIS question was and is NO. That explaining to the OP'er that from any place to near a BH is no place to be interested in what you might or might not be able to see would be secondary to getting away from there...quickly.

The whole of the known Universe is seen to be expanding.. If one of us thinks that our view is distorted by the fact that we are looking out from shrinking space time...
Where is the evidence of this ?

Strange
2011-Aug-24, 08:32 PM
The BHs event horizon is not a true horizon when viewed from the inside.

It is, for the standard definition of an event horizon.


but someone inside CAN see events that have happened outside. a photon can travel from outside of the EH to hit my eye if I am on the inside of the EH ...

That has nothing to do with the fact it is an event horizon.

But it does demonstrate, yet again, how very different it is from the cosmological event horizon.

Strange
2011-Aug-24, 08:34 PM
Which is my point. The fact that Friedman-Robertson-Walker (FRW) spacetime expands does not mean that GR can not expand spacetime.

Huh? FRW is GR. I don't understand what you are saying.


in the case of someone freefalling into a BH GR is expanding space time the deeper into the hole the observer goes.

I don't really know what that means and I have no idea if it is true or not. Are you saying that space (or spacetime) inside the black hole is expanding?

Tensor
2011-Aug-24, 09:20 PM
Which is my point. The fact that Friedman-Robertson-Walker (FRW) spacetime expands does not mean that GR can not expand spacetime.

The FRW spacetime can also contract. Which is directly opposite of what you are saying. The only requirement is that FRW spacetime can't be static.


in the case of someone freefalling into a BH GR is expanding space time the deeper into the hole the observer goes.

You're spouting nonsense now. Unless, of course, you'd like to provide us with the equations showing this.

I'll also note that you have not provided us with any kind of comment on the paper showing the differences in the two singularities. So, any kind of comment you make, such as this one on Strange's comment in post #75:



It was the first, and rather fundamental, difference raised between a black hole and the universe. If you are in a black hole, the singularity is in the future. The big-bang singularity is in the past. Ergo, we are not in a black hole.
That logic sounds faulty. Just because there was a singularity in the past and a singularity in the future which are not the same doesnt mean that there cant be both. Just because A does not equal B does not mean that C does not equal C.

is just more nonsense. That paper I linked to (in post #45), which you seemed to have seen fit to ignore, specifically shows how they are different and why they cannot be the same. So, unless you can show us exactly how that paper is wrong, your arguments are specious.

Jeff Root
2011-Aug-24, 11:44 PM
in the case of someone freefalling into a BH GR is expanding
space time the deeper into the hole the observer goes.
You're spouting nonsense now. Unless, of course, you'd like to
provide us with the equations showing this.
Tom expressed it very poorly, and I'm not going to try
to provide any equations, but I agree with what Tom
appears to mean. My understanding, based in part on
Kip Thorne's "Black Holes & Time Warps", is that GR
predicts that once matter collapses within its own
Schwarzschild radius, it will collapse forever. As it
does so the spacetime around it becomes increasingly
"curved". In colloquial terms, the depth of the gravity
well increases without limit. It is forever approaching
infinite curvature and infinite depth more closely. The
depth of the gravity well is a function of the time since
the black hole formed.

The increasing curvature and increasing depth of the
gravity well is a stretching of spacetime in the radial
direction. That direction is also the time direction, as
spacetime becomes more and more "timelike" the
closer you get to the singularity.

In ordinary space, spacetime is much more "spacelike"
than timelike. At the Schwarzschild radius -- the event
horizon of a black hole -- spacetime is balanced between
spacelike and timelike. At the singularity it is completely
timelike.

This "stretching" of spacetime in a black hole appears to
me to be an increase in the "amount" of spacetime -- in
other words, a kind of expansion akin to although quite
different from the cosmological expansion of space.
Note that although the depth of the gravitational well
increases without limit, that expansion is only in one
direction, and the other directions are progressively
constricted as the well deepens, so that the increase
in the amount of spacetime is finite and very limited.

-- Jeff, in Minneapolis

Strange
2011-Aug-25, 12:01 AM
Well interpreted Jeff :) (If it is, indeed, what tommac meant.) And that, of course, is just yet more evidence that being inside a black hole is very different from being in the universe as we know it.

WayneFrancis
2011-Aug-25, 01:04 AM
And I believe I showed you how it can be manipulated in a way where it would work. I any case this is totally off topic for this thread. If you want to revisit this either please ask for that thread to be reopened or start a new thread at httphttp://www.againstthemainstream.com (http://www.spacetimeandtheuniverse.com) and we can finish that discussion.


mmm I'll bite my tongue on this one




It is not a flaw ... it was intended as a simplification to question a statement that was made. Someone ( I think astromark ) stated that

This was to question if his statement is indeed true and if it is ( or isnt ) to clarify it for the original poster.
Personally I dont think his question is as straight forward as people on here are making it out to be ... There seem to be answers but lets delve a little bit into what is behind the replies.



Is it ... you use the word "drastically" however it seems that the only difference you pose is that the expansion of space is congruent in all directions where falling towards a gravitational source is not. ( something that we can debate on a different thread ) In any case, at minimum, I wouldnt call that drastic.

Tommac you keep ignoring much of what is being said.

We are talking about how space expand in the normal model of cosmic expansion and how space/time would expand and contract for an observer free falling into a black hole.

The first is symmetric in all directions.
The latter is

not symmetric in the direction of motion
perpendicular to the direction of motion is actually contracting instead of expanding.


That is pretty drastic difference. If you are in Texas and jump into a car with a friend to head to California and your friend drives to Florida that is a pretty drastic difference

Or in another analogy. You have 100 friends in a circle around you and you tell them that you want them to walk straight away from you at 5km/hr so that you have this ever increasing perfect circle of friends.
But instead this is what they do is:
The Person to the North of you walks away at 5.5km/hr
The person to the South of you walks away at 4.5km/hr
The person to the East and West walk towards you at 2.5km/hr
The other people between each of them walk in a slightly different direction.
So at the end instead of getting a perfect circle with you at the centre you get
this ever elongated oval where you are slowly moving from the centre of all of them and closer to the southern person then the northern one.

That is drastically different then what you told them all to do.

WayneFrancis
2011-Aug-25, 01:35 AM
Guess I am still missing the point ... can you please explain how that is any different from me watching stuff fall through the EH from the inside?

And BTW this was your EXACT quote:

I don't have an easy explanation for this. It has to do with how the free faller's light cone, for lack of a better word, rotates as it the observer falls through the EH of a black hole and the space like dimension, in the direction of the singularity turns into a time like dimension. Once inside the EH there is no direction to the EH. There is only a past light cone to the EH. Like I said it is just going to confuse the issue more and doesn't really matter.

There are plenty of events that an observer falling into a black hole will never see. The free falling observer has an event horizon associated with them because there is a finite amount of time that the free falling observer
will be able to observe and this time is completely a function of the mass of the black hole and how long it took the free faller to get to the EH of the black hole in their own proper time. It is this finite amount of proper time the observer has that dictates the difference.

Now take an observer in flat space. Say object A is beyond the current cosmic event horizon and essentially getting further away. If expansion started to slow down light from that object would then be capable of gaining ground and making progress towards the observer. Eventually the observer would be able to make observations but if the expansion rate started increasing again the object could once again pass out of our cosmic event horizon and we would stop being able to observe it.

This does not happen with a free falling observer into a black hole. You can calculate what event you could see by working out your proper time to the singularity. Anything further away then that will never be able to catch up to you. Simple as that. IE your future light cone is limited to the amount of proper time you have left.

WayneFrancis
2011-Aug-25, 01:39 AM
Why do you keep stating this ... I dont think anyone is stating anything else.

Well if you are talking about a free faller inside a black hole and an observer in flat space looking out at the universe this is very relevant. Unless you want to say "They both look the same...unless you open your eyes...so don't open your eyes and pretend you don't know what has been observed.

WayneFrancis
2011-Aug-25, 01:43 AM
Why would we think it would be contracting? Would it be contracting? I would think that looking out from the interior of a BH ( from inside the EH ) or even falling in that space would be expanding not contracting.

For the 10th time, yes it would be contracting in directions perpendicular to the direction of motion. So you would think wrong.

WayneFrancis
2011-Aug-25, 01:45 AM
Hand wave?

First that isn't the post where I said you hand wave things.

Second are you asking for a definition of "hand waving"?

Jeff Root
2011-Aug-25, 01:49 AM
Once inside the EH there is no direction to the EH.
The meaning of the word "to" in that sentence appears to be
absolutely critical. I think you should explain what you mean
by "to" in as much detail as possible.



The free falling observer has an event horizon associated with
them because there is a finite amount of time that the free falling
observer will be able to observe ...
That's probably true for everyone, not just people falling into a
black hole.

-- Jeff, in Minneapolis

tommac
2011-Aug-25, 02:04 AM
Well interpreted Jeff :) (If it is, indeed, what tommac meant.) And that, of course, is just yet more evidence that being inside a black hole is very different from being in the universe as we know it.

Yes this is in sync with what I meant.

tommac
2011-Aug-25, 02:06 AM
Uggg ... how am I ignoring this ... I stated that this was a very good argument why we are not in a black hole. So I am accepting that this is a good reason.

I dont think it is a "drastic" difference but a pretty good argument.


mmm I'll bite my tongue on this one




Tommac you keep ignoring much of what is being said.

We are talking about how space expand in the normal model of cosmic expansion and how space/time would expand and contract for an observer free falling into a black hole.

The first is symmetric in all directions.
The latter is

not symmetric in the direction of motion
perpendicular to the direction of motion is actually contracting instead of expanding.


That is pretty drastic difference. If you are in Texas and jump into a car with a friend to head to California and your friend drives to Florida that is a pretty drastic difference

Or in another analogy. You have 100 friends in a circle around you and you tell them that you want them to walk straight away from you at 5km/hr so that you have this ever increasing perfect circle of friends.
But instead this is what they do is:
The Person to the North of you walks away at 5.5km/hr
The person to the South of you walks away at 4.5km/hr
The person to the East and West walk towards you at 2.5km/hr
The other people between each of them walk in a slightly different direction.
So at the end instead of getting a perfect circle with you at the centre you get
this ever elongated oval where you are slowly moving from the centre of all of them and closer to the southern person then the northern one.

That is drastically different then what you told them all to do.

WayneFrancis
2011-Aug-25, 02:07 AM
OK a few things. 1) again you are talking about an external observer trying to look into an EH. That is wrong and off topic. It is NOT what is being discussed.


No tommac, what I'm saying is that a free faller has an effective personal EH. The free faller doesn't get to see the everything in the universe. They have a finite amount of time and thus have a finite amount of stuff they can see. This means there are events, which I'm defining as something that occurs in a particular point in space and time, that will never be able to effect them. IE there are events within our Cosmic event horizon that an external observer will be able to observe that a free faller won't once the free faller passes the EH of the black hole. It is an EH for the free faller that acts like the cosmic EH except for the cosmic event horizon can change size for an external observer, based on the formula I provided before, while this EH of the free faller is calculated completely by the mass of the black hole.





2) What would make you think that the scale factor is going to change? How would that be different from say a BH evaporating?

The scale factor has been changing for the last 13.75 billion years.




How would that be different from say a BH evaporating?


Well BH evaporating only significantly effects very small black holes. Even a black hole with the mass of the moon which looses more mass then it gains would last many orders of magnitude longer then the age of the universe which is even much longer then the proper time of the free falling observer once they have passed the EH of said black hole. Now you are talking about a black hole with the mass of the observable universe which would evaporate even slower.

Are you trying to suggest that the universe is evaporating mass like a black hole via HR is causing the changing scale factor of the universe?

tommac
2011-Aug-25, 02:08 AM
I understand that no matter what direction the freefaller looks the path will lead to the singularity ... But what I think you are missing is that some paths are longer than others ... so if I am looking outward ( yes I know that it still would be towards the singularity ... but the longest path ) and someone shined a flashlight directly towards me I would see that light


I don't have an easy explanation for this. It has to do with how the free faller's light cone, for lack of a better word, rotates as it the observer falls through the EH of a black hole and the space like dimension, in the direction of the singularity turns into a time like dimension. Once inside the EH there is no direction to the EH. There is only a past light cone to the EH. Like I said it is just going to confuse the issue more and doesn't really matter.

There are plenty of events that an observer falling into a black hole will never see. The free falling observer has an event horizon associated with them because there is a finite amount of time that the free falling observer
will be able to observe and this time is completely a function of the mass of the black hole and how long it took the free faller to get to the EH of the black hole in their own proper time. It is this finite amount of proper time the observer has that dictates the difference.

Now take an observer in flat space. Say object A is beyond the current cosmic event horizon and essentially getting further away. If expansion started to slow down light from that object would then be capable of gaining ground and making progress towards the observer. Eventually the observer would be able to make observations but if the expansion rate started increasing again the object could once again pass out of our cosmic event horizon and we would stop being able to observe it.

This does not happen with a free falling observer into a black hole. You can calculate what event you could see by working out your proper time to the singularity. Anything further away then that will never be able to catch up to you. Simple as that. IE your future light cone is limited to the amount of proper time you have left.

tommac
2011-Aug-25, 02:10 AM
First that isn't the post where I said you hand wave things.

Second are you asking for a definition of "hand waving"?

No I was questioning your overuse of analogies to irrelevant things ... was wondering if it was your jedi hand wave technique.

tommac
2011-Aug-25, 02:15 AM
well that is what you are saying now ... not what you have been saying. The free faller has an effective personal EH as I explained to you in another thread, but not sure if you totally understand it yet.

You are right saying that the free faller has a limited amount of time so can only see things that would reach him in that time ... but that is not a horizon by any definition.

The effective personal EH is something different ... and is limited when the free faller and space-time is being pulled at a rate faster than the speed of light into the singularity ... ( in some ways similar to the edges of visible universe. )

Again I am not suggesting anything. Just trying to make sense of many statements being thrown out here.


No tommac, what I'm saying is that a free faller has an effective personal EH. The free faller doesn't get to see the everything in the universe. They have a finite amount of time and thus have a finite amount of stuff they can see. This means there are events, which I'm defining as something that occurs in a particular point in space and time, that will never be able to effect them. IE there are events within our Cosmic event horizon that an external observer will be able to observe that a free faller won't once the free faller passes the EH of the black hole. It is an EH for the free faller that acts like the cosmic EH except for the cosmic event horizon can change size for an external observer, based on the formula I provided before, while this EH of the free faller is calculated completely by the mass of the black hole.





The scale factor has been changing for the last 13.75 billion years.





Well BH evaporating only significantly effects very small black holes. Even a black hole with the mass of the moon which looses more mass then it gains would last many orders of magnitude longer then the age of the universe which is even much longer then the proper time of the free falling observer once they have passed the EH of said black hole. Now you are talking about a black hole with the mass of the observable universe which would evaporate even slower.

Are you trying to suggest that the universe is evaporating mass like a black hole via HR is causing the changing scale factor of the universe?

tommac
2011-Aug-25, 02:17 AM
The scale factor has been changing for the last 13.75 billion years.

And what makes you think it can stop and change back?

WayneFrancis
2011-Aug-25, 02:20 AM
Example please ... never heard of this EH that follows the free faller from behind. Is there a name for this EH that follows the free faller in?

I have please read them





And I am saying you can.


Reread my quote. Me saying "I'm not saying you can't see something that appears behind you" = you saying "I am saying you can see something behind you"

This is very different from what I'm saying "You can't look in the direction of the EH because there is no direction you can travel in to get to the EH once you are inside it."



Say we have a space ship and we are dropping prisoners into the EH from a safe distance. Each one has a flash light. We drop the prisoners at an arbitrary rate ... As the first prisoner passes the EH ... he will continue to see the light from all of the other flashlights ( until space between them is expanding at a rate of > 2c ???) ( not sure if it is c or 2c due to ant and a rope. )

Again I disagree here. There are infinite directions inside the EH ... all of which eventually lead to the singularity. But there are still infinite directions .... some of those directions are back towards to the EH. What I am saying here is that I can look in the direction of the EH even though space is curved.



Once past the EH the EH is forever in your past light cone. Never in your future light cone. There is no direction that brings you closer to the EH. All directions lead you towards the singularity. Don't mistake past light cone with direction which you can travel.




Stuff ( say photons of light ) can flow from outside of the EH and I can look at it. Can my eye travel outside the EH ... obviously no. But the same way that I can look up and see a distant star from here on earth ... I can look out from inside the EH and see light (possibly even from the same distant star ).

And there is a limited amount of time in which photons will reach your eye will be able to see once inside the EH. This means anything further away from you then that is outside of your light cone. Which is the same as saying they are beyond an event horizon of yours. This EH is unique to you. Other observers will have different EH's and all these EH's are very different from the EH of the black hole.

WayneFrancis
2011-Aug-25, 02:22 AM
Friedman-Robertson-Walker (FRW) spacetime expands, but one of the requirements is that it is of uniform density (homogeneous
and isotropic). This is not true of a black hole. So if you are claiming that spacetime expands in a black hole, then no.

Thanks Strange. This is what I've been trying to explain to by pointing out that a free falling observer is experiencing forces different then an external observer in flat space.

WayneFrancis
2011-Aug-25, 02:29 AM
This has to do to try to figure out what you mean by statements like:



while we all agree with you we are looking for a bit more detail in these sort of statements. So lets start with ... how can this be ruled out? How do we know we are not?

And we are also discussing it because it seems that many of the arguments which are based on looking into an EH, which no one is claiming ... that space does not expand as one falls into an EH ... which is not true, that 'Shrinking to a event horizon' which I am not sure what it means ... that you cant see stuff external to EH from inside the EH ... which is not true.

Nobody is claiming that the universe is inside of a black hole ... we are asking these question to figure out which are valid arguments as to why it is not.

I am not satisfied with accepting blindly that it is not based on a bunch of handwaving, distractions, and false or misguided statements.

So maybe we can start over ...

What are the strongest arguements that we are not in a black hole and what are the main differences of an expanding universe and looking from the inside of a BH outwards?

wayne has a decent argument ... which is that space does not expand equally in all directions. So we can start with that as the main ( and only valid ) argument that I have seen so far in this thread ... lets add a few more to help answer the Original Question.

Why do you have to go beyond that one? If you hit a fatal flaw in a model you don't discount the observations that highlighted that fatal flaw and move on like those observations where not there.

If I say "All swans are black! Why are all swans black?" and then look at 100 swans and see 50 black and 50 white ones do you discount the 50 white ones and repeat the question "Why are all swans black?". No, we don't.

csmyth3025
2011-Aug-25, 02:34 AM
...In ordinary space, spacetime is much more "spacelike"
than timelike. At the Schwarzschild radius -- the event
horizon of a black hole -- spacetime is balanced between
spacelike and timelike. At the singularity it is completely
timelike...

-- Jeff, in Minneapolis
I agree that there are distinctions that illustrate why we don't live in a black hole. The differences have been thoroughly discussed.

I'm trying to reconcile your above quoted statement with my understanding of what "spacelike" and "timelike" mean. At my level of education I have only the defininitions provided by Wikipedia to guide me:


For two events separated by a time-like interval, enough time passes between them for there to be a cause-effect relationship between the two events. For a particle traveling through space at less than the speed of light, any two events which occur to or by the particle must be separated by a time-like interval. Event pairs with time-like separation define a negative squared spacetime interval (s2 < 0) and may be said to occur in each other's future or past. There exists a reference frame such that the two events are observed to occur in the same spatial location, but there is no reference frame in which the two events can occur at the same time.

(ref. http://en.wikipedia.org/wiki/Spacetime#Time-like_interval )

-and-


When a space-like interval separates two events, not enough time passes between their occurrences for there to exist a causal relationship crossing the spatial distance between the two events at the speed of light or slower. Generally, the events are considered not to occur in each other's future or past. There exists a reference frame such that the two events are observed to occur at the same time, but there is no reference frame in which the two events can occur in the same spatial location.

(bold added by me)
(ref. http://en.wikipedia.org/wiki/Spacetime#Space-like_interval )

Given these definitions (assuming they're correct), how is it that "...in ordinary space, spacetime is much more 'spacelike' than timelike..."?

I thought that everything in our observable universe is, by definition, within our past light cone. Haven't the distant cosmological things that we observe all occurred "in our past"?

I suppose what I'm trying to say is that it seems to me (given the above definitions) that events that are separated from us by a spacelike world-line are, and always will be, outside of our observable universe.

Chris

tommac
2011-Aug-25, 02:34 AM
This is very different from what I'm saying "You can't look in the direction of the EH because there is no direction you can travel in to get to the EH once you are inside it."
.

I get your point ... but you can look in the direction with the longest path to the singularity ... when looking in that direction you can see light coming from outside of the EH

Jeff Root
2011-Aug-25, 02:37 AM
Wayne,

The question Tom is asking is not the title question of this thread,
"Are we in a black hole?" The question he is asking is, "How is
being in the Universe different from being in a black hole?" Since
there are similarities, he wants to know the differences.

-- Jeff, in Minneapolis

Swift
2011-Aug-25, 02:40 AM
Given that the OP with the question left us a long time ago, we are well over 100 posts, and we are rather off from the original question, this thread is moved from Q&A to Astronomy.

I am so tempted to make some sort of joke about "are we in a Black Hole?" - yes a BAUT black hole thread, from which there is no escape and within which the normal laws disappear, but that would probably be inappropriate... so forget I even mentioned it. :)

tommac
2011-Aug-25, 02:49 AM
yes and waynes point with the expansion of space in one direction vs all directions is definitely one of the differences.


Wayne,

The question Tom is asking is not the title question of this thread,
"Are we in a black hole?" The question he is asking is, "How is
being in the Universe different from being in a black hole?" Since
there are similarities, he wants to know the differences.

-- Jeff, in Minneapolis

tommac
2011-Aug-25, 02:51 AM
I am just trying to separate the black swans from the white swans not discounting any of them



Why do you have to go beyond that one? If you hit a fatal flaw in a model you don't discount the observations that highlighted that fatal flaw and move on like those observations where not there.

If I say "All swans are black! Why are all swans black?" and then look at 100 swans and see 50 black and 50 white ones do you discount the 50 white ones and repeat the question "Why are all swans black?". No, we don't.

Jeff Root
2011-Aug-25, 03:06 AM
Chris,

Spacetime is most "spacelike" farthest from any source of
gravity. It is most spacelike where it is the "flattest". The
greater the spacetime curvature, the more "timelike" it is.
At the surface of the Earth, spacetime has enough of a
timelike character to provide an acceleration of 9.8 m / s^2,
which is a pain in the butt. At 150 million km from the Sun.
it is timelike enough to make us run around in circles at
30 km / s. So it is far from being *purely* spacelike. Even
at extreme distance from any source of gravity, spacetime
has a time component, so it is never purely spacelike.
But outside the event horizon of a black hole, it is more
spacelike than timelike.

That was just one way to try to answer your objections.
I don't understand it well enough to give a really good answer.
If my answer wasn't satisfactory, do press for a better one!

-- Jeff, in Minneapolis

WayneFrancis
2011-Aug-25, 03:09 AM
Although the math would be nice ...
It is clear that spacetme expands due to the blue shift.

How is that clear? What blue shift?

Perhaps you should show the maths to back up your claim? I always thought red shift was associated with expansion.

WayneFrancis
2011-Aug-25, 03:26 AM
The fact that the big-bang singularity is in the past not the future (see post #3) is another.

The BH's EH is in the past also ( for something that has already passed it.)

So? The EH is in an external observer future light cone and in to a free falling observer inside the EH it is in their past light cone.
This doesn't change the fact that the black hole's singularity is ALWAYS in an observer's future light cone until they hit it and the big bang's singularity is ALWAY in an observers past light cone.

You've, knowingly or not, pulled a bait and switch and it just confuses the issue. The Strange's point #3 was about the singularities and not the EH.

WayneFrancis
2011-Aug-25, 04:30 AM
Sorry I should have been doing this earlier but it is a lot easier to answer 1 post at a time for me. IE I can keep track better.
Sorry for the million posts.



Reread ... it has everything to do with being an external observer or not. Remember we are not looking at the EH of the BH as a true horizon ... we can see past the horizon ... we can see distant stars ... this is very different than what is being explained in post 46 and has already been addressed in replies to that post.

No you don't see the distance stars. What you see are photons that where right behind you. When you pass the EH of a black hole all the information you receive after that point has also already passed the EH. You claim to understand what I, sounding like a broken record, and others keep saying then hand waving it away and claiming it doesn't have anything to do with what you are asking.

Its like a someone asking "What is 4 + 4" and some else saying "8" and then the original person saying "I know what 8 is but I'm asking what 4 + 4 is".

The maths of what a free faller sees is honestly way beyond me but if you look around there are web casts by people like Susskind that explain what actually happens to free fallers through a black hole and why 2 people separated by a small distance never seem to loose contact even though they pass through the black hole's EH at different times and most importantly why there is a finite amount time period for which those 2 observers can receive event. When an observer commits to passing the EH the light cone of that observer drastically changes and it is primarily a function of the mass of the black hole or if you want the size of the black hole but since for a non rotating black hole these have a direct correlation it is 6 of one or a half dozen of the other.


What does this have to do with ANYTHING?

It has to do with the fact that you pulled a bait and switch that can make it look like Strange made a mistake to a lurker AND we are talking about the differences between an expanding universe and a free faller inside a black hole. I keep trying to stop at one flaw. Strange just brought up 3 more that you want to hand wave away.


That logic sounds faulty. Just because there was a singularity in the past and a singularity in the future which are not the same doesnt mean that there cant be both. Just because A does not equal B does not mean that C does not equal C.

No, what strange is saying is A = BH singularity in the future, B = BB Singularity in the past
A != B
It doesn't matter if the observer is inside or outside of the EH of a BH
A != B when observer's d > rs
A != B when observer's d < rs

Please tell use what C = C you think you are talking about.



Can you please provide an example of how the scale factor can change? Also which Black Hole horizon are you talking about? The EH as observed externally?

Like I've said before. The scale factor changes with time and not only is it changing with time, which was easily predicted, but it the rate at which it is changing is increasing which was not expected. But since we don't understand dark energy enough we can't make any conclusive statements about the rate continueing to increase

Please read http://en.wikipedia.org/wiki/Scale_factor_(cosmology)

Are you trying to claim that the scale factor of the universe was the same 1 billion years after the big bang as it is now?





Also which Black Hole horizon are you talking about? The EH as observed externally?
The event horizon at the Schwarzschild radius. Is there another.

*Sigh* this is what I was afraid of. He might be talking about me saying that a free faller has a personal event horizon once they pass the EH of the black hole. IE there are suddenly events the free faller will never recieve information about because they'll basically slam into the singularity before any information about those events could catch up to them. It is an event horizon in that respect but I didn't like coopting the term for it because it is a bit confusing if he doesn't play around with the light cones to see what happens. Really he should love this because it's something that you can play with picture and see in a 2D representation without doing lots of maths but I'm not going to spend hours butchering up some diagrams showing what happens with the light cones.



Then it is easy to see the light emmited from objects behind the Schwarzschild radius.

Even from distant galaxies.

Only the light from those galaxies that was right behind you. For a BH with a Rs = 1au you'll only see ~8min 20 seconds more light from that galaxie while an external observer will observe as much as they want.



Again ... you are confusing looking at a black hole from an external viewpoint. From inside the expansion of space is time dependant. ( the more time you freefall the more the universe will appear to expand ). As a freefaller your time is set space becomes timelike.

What we need to be careful of is not referrring to the BH from how we understand it from an external viewpoint unless we have a way to also look at the universe from an external point of view.

no one spacial dimension, in direction of the singularity, becomes time like in that you can't go backwards.



It doesnt seem like we will progress much further in this discussion ...
But you can see that it is not a straight forward answer. The mainstream answer is no we are not in a black hole as it does not fit into the current mainstream model of how we model/envision the universe. Does that mean that the answer is an absolute no ? ... you decide.

Because you seem to refuse to learn. The answer is complicated but we are talking about a complicated bit of physics here. Just because it is complicated doesn't mean there is doubt. That is a logical falacy. Science isn't about absolute answers. It is about the best current models that match observations and currently there is no observation that points towards what you are suggesting.

Your arguement is much like evolution denying creationist saying that kids should decide for themselves what the scientific facts are.


A singularity in your future would be your cause of death.

Exactly. Pass a BH's EH and the singularity chops off yourlight cone.



The BHs event horizon is not a true horizon when viewed from the inside. For example ... if I was inside I can clearly witness events that are happening outside the EH. It is only an event horizon when you are looking in ... someone outside can not see the events that are happening from inside the EH ... but someone inside CAN see events that have happened outside. a photon can travel from outside of the EH to hit my eye if I am on the inside of the EH ...


No once you pass the EH you witness information from events that have also passed through the EH. The events you can see once inside the EH are a function of the size of the black hole. If the black hole is 1 light minute in radius then you'll only see events that where within 1 light minute of you when you where at the EH. Any event further away then that is not in your future light cone because your future light cone is now castrated by the singularity.

In cosmology the BB's singularity doesn't effect your future light cone at all.



Well interpreted Jeff :) (If it is, indeed, what tommac meant.) And that, of course, is just yet more evidence that being inside a black hole is very different from being in the universe as we know it.

Agreed, that is what I was trying to get at with my "not symmetrical" and my "100 friends in a circle" analogy.

WayneFrancis
2011-Aug-25, 04:37 AM
The meaning of the word "to" in that sentence appears to be
absolutely critical. I think you should explain what you mean
by "to" in as much detail as possible.


That's probably true for everyone, not just people falling into a
black hole.

-- Jeff, in Minneapolis

For the first part there is no spatial direction of travel to get a free faller inside the black hole closer to the EH. All direction are warped so much that they lead away from the EH once inside the EH.

For the second part I'm talking about hypothetical observers that can observe forever. One of these observers outside of the BH have an infinitely increasing cosmic event horizon and this is a function of time. For one of these observers that have passed the EH of a black hole they've effectively cut off their future light cone and thus introduce, at the point they passed the EH, an personal event horizon for which there is nothing that can be done to change the size of that EH.

WayneFrancis
2011-Aug-25, 04:45 AM
Uggg ... how am I ignoring this ... I stated that this was a very good argument why we are not in a black hole. So I am accepting that this is a good reason.

I dont think it is a "drastic" difference but a pretty good argument.

Then why do you make statements like


It doesnt seem like we will progress much further in this discussion ...
But you can see that it is not a straight forward answer. The mainstream answer is no we are not in a black hole as it does not fit into the current mainstream model of how we model/envision the universe. [U]Does that mean that the answer is an absolute no ? .... you decide.

That is about as useful to say to someone as "Does that mean that gravity is what holds us on the surface of the Earth? .... you decide."

Sure call into question a model when observations don't match its prediction. Don't say "Well the model A fits perfectly with the observations and model B isn't consistent with observations at all. Could model B be correct and model A be wrong? .... you decide."

You don't have to decide if 2 = 4.

Tensor
2011-Aug-25, 05:04 AM
Tom expressed it very poorly, and I'm not going to try
to provide any equations, but I agree with what Tom
appears to mean.

If that was his intention, then I misspoke. But, my comment was based on what he wrote.



My understanding, based in part on
Kip Thorne's "Black Holes & Time Warps",

snip...

so that the increase
in the amount of spacetime is finite and very limited.

-- Jeff, in Minneapolis

While I have minor quibbles (based on the math), I'll leave it alone here in the thread. What you wrote is pretty solid conceptually for those looking for a non math type explanation. Good Job.

WayneFrancis
2011-Aug-25, 05:11 AM
I understand that no matter what direction the freefaller looks the path will lead to the singularity ... But what I think you are missing is that some paths are longer than others ... so if I am looking outward ( yes I know that it still would be towards the singularity ... but the longest path ) and someone shined a flashlight directly towards me I would see that light

The longest path to the singularity is the path of free faller. Any movement by the free faller in any direction, from my understanding, actually shortens the proper time the free faller has on their trip to the singularity.

Think of it this way. A free faller paths all curve towards the singularity. let me show you a simple diagram.
http://www.users.on.net/~waynefrancis/bhfreedomofmovement.png

Outside the Event horizon you have 6 degrees of freedom. Inside of the EH you loose 1 degree of freedom or more precisely that degree of freedom snaps to the singularity.
The others also bend to the singularity. Even though the purple lines look longer the light travel time is the same. So you can't slow down. Once inside the EH you've got a maximum time until you reach the singularity and that is equal to Rs in units of time. A black hole that is 1 au in size = a maximum proper time of 8 min 20 seconds and pretty much any movement you do once inside the EH only shortens your proper time.

WayneFrancis
2011-Aug-25, 05:43 AM
well that is what you are saying now ... not what you have been saying. The free faller has an effective personal EH as I explained to you in another thread, but not sure if you totally understand it yet.


This is what I've been saying and is a core point of mine



You are right saying that the free faller has a limited amount of time so can only see things that would reach him in that time ... but that is not a horizon by any definition.


Really? Please tell me where this logic breaks down.
The formula for the cosmological event horizon can be found using the formula
d_{e} = \int_{t_{0}}^{\infty}\frac{c}{a(t)}dt
where d_{e} \neq \infty an event horizon is present.

This event horizon is the same distance for all observers of a given t_{n} but this is because the observer continue to wait for the events at that distance to reach them and the time it would take is d_{e}

Introduce the observer passing the EH of a black hole and the formula now changes to

d_{e} = \int_{t_{0}}^{t_{n} + r_{s}}\frac{c}{a(t)}dt

What makes this not an EH in your eyes? Any event at a point further then d_{e} at the point the free faller hits the EH will never reach the observer. IE it is an EVENT that is forever beyond the observer's ability to see it.

Just like if I'm outside the EH of a black hole. Watch something fall through the black hole, last photon has been emitted, then try to chase after said object I'll never be able to see the object again no matter how hard I try.

WayneFrancis
2011-Aug-25, 05:46 AM
And what makes you think it can stop and change back?

The scale factor has slowed down in the past. Why do you believe it absolutely can't slow down in the future? Do you know details about dark energy that the rest of the worlds scientists don't know? Please come forward, tell us and accept your Nobel prize.

WayneFrancis
2011-Aug-25, 06:52 AM
Wayne,

The question Tom is asking is not the title question of this thread,
"Are we in a black hole?" The question he is asking is, "How is
being in the Universe different from being in a black hole?" Since
there are similarities, he wants to know the differences.

-- Jeff, in Minneapolis

And you, Strange, Cougar, Tensor and myself, sorry if I missed any others, have explained a number of differences only to have him say things like



What does this have to do with ANYTHING?


...
Is it ... you use the word "drastically" however it seems that the only difference you pose is that the expansion of space is congruent in all directions where falling towards a gravitational source is not. ( something that we can debate on a different thread ) In any case, at minimum, I wouldnt call that drastic.

Here is post #52 we see




The EH of a black hole is different then the EH of our Hubble sphere.
Why do you keep stating this ... I dont think anyone is stating anything else.

but then in post #66


This is again going back to the questions that we are trying to answer .... To ask the question again ... HOW is the cosmological event horizon different from looking out to the EH from inside of the EH a black hole? It seems that the way you pose this statement is from an external observer looking into a BHs EH. Which is faulty logic.

So he agrees with the explanation on how the 2 are different, forgets that the explanations have been given to him then tries to claim we are sayins something different then we have and that our logic is faulty.


So lets summarise just some of the differences to the question

How is being in the Universe different from being in a black hole?


The universe has the singularity in its past light cone. The singularity of a black hole terminates the future light cone of a free falling observer.
The universe has expansion which is symmetric in all directions. The distortion of space time inside a black hole is far from symmetric.
The event horizon of the universe is determined by the formula d_{e} = \int_{t_{0}}^{\infty}\frac{c}{a(t)}dt and dark energy is not understood enough to say much about the future rates of expansion thus while something may be currently beyond our cosmic event horizon in the future it may not be. While for a free falling observer inside the EH of a black hole they have a personal cosmic event horizon given by the formula of basically d_{e}=r_{s} with respect to the free falling observer.
The universe's density is homogeneous and isotropic. The density of a black hole is not.
The whole paper Tensor linked in post #45


I'd start with that last one first since it is peer reviewed.

Usher
2011-Aug-25, 07:42 AM
And you, Strange, Cougar, Tensor and myself, sorry if I missed any others, have explained a number of differences only to have him say things like






Here is post #52 we see


but then in post #66



So he agrees with the explanation on how the 2 are different, forgets that the explanations have been given to him then tries to claim we are sayins something different then we have and that our logic is faulty.


So lets summarise just some of the differences to the question



The universe has the singularity in its past light cone. The singularity of a black hole terminates the future light cone of a free falling observer.
The universe has expansion which is symmetric in all directions. The distortion of space time inside a black hole is far from symmetric.
The event horizon of the universe is determined by the formula d_{e} = \int_{t_{0}}^{\infty}\frac{c}{a(t)}dt and dark energy is not understood enough to say much about the future rates of expansion thus while something may be currently beyond our cosmic event horizon in the future it may not be. While for a free falling observer inside the EH of a black hole they have a personal cosmic event horizon given by the formula of basically d_{e}=r_{s} with respect to the free falling observer.
The universe's density is homogeneous and isotropic. The density of a black hole is not.
The whole paper Tensor linked in post #45


I'd start with that last one first since it is peer reviewed.

:clap:

Jeff Root
2011-Aug-25, 10:45 AM
Here in post #52 we see



The EH of a black hole is different than the EH of our Hubble sphere.
Why do you keep stating this ... I dont think anyone is stating anything else.
but then in post #66



This is again going back to the questions that we are trying to answer ....
To ask the question again ... HOW is the cosmological event horizon
different from looking out to the EH from inside of the EH a black hole?
It seems that the way you pose this statement is from an external
observer looking into a BHs EH. Which is faulty logic.
So he agrees with the explanation on how the 2 are different, forgets
that the explanations have been given to him then tries to claim we are
saying something different then we have and that our logic is faulty.
I'm afraid I agree with Tom.

He didn't forget anything. What he said in the second quote
doesn't conflict with what he said in the first quote. The question
for you is what Tom thinks your faulty logic was. Tom said that it
appears you were talking about what an external observer sees.
That would be an illogical reply from you if you were in fact talking
about what an external observer sees, because Tom asked what
an internal observer would see. The comparison is between what
the Universe looks like from the inside and what a black hole looks
like from the inside. He agrees with what you said about what a
black hole looks like from the outside, but that doesn't address
his questions.

I'm not sure because I didn't go back and check, but I think some
or all of his other statements that you reference may be about this
same apparent disconnect between his questions and your replies.

-- Jeff, in Minneapolis

tommac
2011-Aug-25, 02:16 PM
The universe has the singularity in its past light cone. The singularity of a black hole terminates the future light cone of a free falling observer.

I understand there is a difference between the two singularities but wouldnt someone inside a BH have both anyway? So not really sure why this would be an argument that we are not inside of a EH.





The universe has expansion which is symmetric in all directions. The distortion of space time inside a black hole is far from symmetric.


This is valid ... although I believe one could create a model where the forces are equal. ( not to be dicussed here in this thread if you want reopen original thread or open a new thread at http://www.againstthemainstream.com (http://www.spacetimeandtheuniverse.com)



The event horizon of the universe is determined by the formula d_{e} = \int_{t_{0}}^{\infty}\frac{c}{a(t)}dt and dark energy is not understood enough to say much about the future rates of expansion thus while something may be currently beyond our cosmic event horizon in the future it may not be. While for a free falling observer inside the EH of a black hole they have a personal cosmic event horizon given by the formula of basically d_{e}=r_{s} with respect to the free falling observer.


I think your second formula is wrong. But I am not the expert. However I need to question a formula that does not take the expansion of space-time or any time factor. Firstly because space is timelike within the EH and also we are talking about the observation of distant galaxies which are getting farther away due to relativistic effects as the freefaller gets deeper into the hole.




The universe's density is homogeneous and isotropic. The density of a black hole is not.


How do we know? Can you show a reference?




The whole paper Tensor linked in post #45


The paper that Tensor linked to was very good but did not ( or at least I didnt see it ) discuss looking out from the inside. If it does discuss this please link or quote the part that does.

tommac
2011-Aug-25, 04:05 PM
The longest path to the singularity is the path of free faller. Any movement by the free faller in any direction, from my understanding, actually shortens the proper time the free faller has on their trip to the singularity..

Sorry just seeing this ... I think that you are partially right ... the curvature part is right.... but... From my understanding crossing the event horizon of a SMBH would seem like a non-event for the freefaller ...
Basically if his friend was a mile away with a flashlight he would see it the same way that he did before crossing. The point here is that the light is travelling faster towards the singularity than the freefaller ... it is travelling at the speed of light along a path that is curved to the singularity .... therefor it can overcome and be observed by the freefaller who is just freefalling ( kind of moving along with the curvature ).

Light from distant galaxies can still be detected from inside the EH. Events from outside of the EH can still be observed by someone inside the EH.

WayneFrancis
2011-Aug-26, 04:58 AM
Sorry just seeing this ... I think that you are partially right ... the curvature part is right.... but... From my understanding crossing the event horizon of a SMBH would seem like a non-event for the freefaller ...
Basically if his friend was a mile away with a flashlight he would see it the same way that he did before crossing. The point here is that the light is travelling faster towards the singularity than the freefaller ... it is travelling at the speed of light along a path that is curved to the singularity .... therefor it can overcome and be observed by the freefaller who is just freefalling ( kind of moving along with the curvature ).

Light from distant galaxies can still be detected from inside the EH. Events from outside of the EH can still be observed by someone inside the EH.

Tommac, for the billionth time I understand that the free falling observer can see behind them before, during and after they cross the event horizon. I understand that you understand that they can SEE behind them the entire time. What I'm saying is that they can not TRAVEL in that direction because for them that isn't a valid space like dimension. That is where the dimension, radially out from the singularity, can only be travelled in one direction. Like time. We can only travel forward in time even though we can look backward in time.

Again if you play with light cones you might not get confused with the time like dimension and the space like dimension.

I understand that my first post in #35 was poorly worded.

In post 46 I clarified what I was saying



Doesn't matter if you are inside or outside the EH of the BL. Once inside the EH of a black hole there is a EH that follows you right behind you. Now I'm not saying that you can't see something that appears to be behind you. What I'm saying is you can't look at the EH. Inside the EH there is no direction that points anywhere but the singularity. You still have a past future light cone where you can receive information that was further out then you but you can't look in the direction of the EH because there isn't one. This though is just confusing the issue more.

There are a few threads that describe very nicely what actually happens with the light cones of a free falling observer as they fall past the EH of a black hole.

Now in the phrase "EH that follows you right behind you." "right behind you" is d_{e} = r_{s}

Any event that happens further away then 2x the Schwarzschild radius in spacetime coordinates will never reach you. This is an Event Horizon.

IE I have the following scenario.

Observer A is 10 light minutes from a black hole with a EH of 1au or ~8.33 light minutes.
Observer B is 5 light minutes from the EH of the same black hole.
Observer C is falling into the black hole.
Using their knowledge of GR they all agree to flash a laser at the same time which is when C hit the EH of the Black hole.

What is the result?

A will see B's light red shifted
B will see A's light blue shifted
B won't see A's Light at all
C won't see A's light at all
C will see B's light about 5 minutes after passing the EH
C will never see A's light because C will hit the singularity before the photons from A will catch up to them.

caveman1917
2011-Aug-28, 06:49 AM
Outside the Event horizon you have 6 degrees of freedom. Inside of the EH you loose 1 degree of freedom or more precisely that degree of freedom snaps to the singularity.

This is not completely correct. It is true that the radial dimension which was spacelike outside turns timelike inside, but the reverse is also true. What is time outside becomes space inside. So you're not losing degrees of freedom, you're switching them. You lose one but you gain another, if you will. The EH will be past and the singularity future where they were spatial outside, but what is future and past outside become spatial inside. That second bit is oft forgotten, it is not just that the radial spatial dimension becomes timelike but also that the timelike dimension becomes spatial.

This is for example why the volume of a black hole is practically infinite. What is to us the lifetime of a black hole (infinite) is spatial inside the black hole, ergo infinite volume.

* Hawking radiation makes it disappear, but if you just take a GR view it has an infinite lifetime.

WayneFrancis
2011-Aug-28, 11:26 AM
How is the time like dimension thought to be manifested into a space like dimension once inside the EH?

tommac
2011-Aug-28, 11:40 AM
How is the time like dimension thought to be manifested into a space like dimension once inside the EH?
who knows ... why are you asking?

tommac
2011-Aug-28, 11:45 AM
What I'm saying is that they can not TRAVEL in that direction because for them that isn't a valid space like dimension.
Who said anything about travel ... the case is simple ... a freefaller ( so no "TRAVEL" other than the free fall ) ... looking back towards the furthest point away from the singularity .... looking at the universe ...

tommac
2011-Aug-28, 11:48 AM
C will see B's light about 5 minutes after passing the EH

and will see it as blue shifted.

caveman1917
2011-Aug-28, 04:33 PM
How is the time like dimension thought to be manifested into a space like dimension once inside the EH?

What do you mean by "manifested"?
The same way the radial dimension is thought to be manifested as a timelike dimension, it switches sign in the metric. Meaning that when you do particle trajectories they will now have the freedom to move back and forth in the dimension which outside is time.

Jeff Root
2011-Aug-28, 05:04 PM
C will see B's light about 5 minutes after passing the EH
and will see it as blue shifted.
Everything falling into a black hole is pulled apart radially.
That means the free-faller is pulled away from the incoming
light, so he sees it as redshifted.

If the free-faller stopped being a free-faller and slowed his
fall with a rocket, he could see the light as blueshifted.

-- Jeff, in Minneapolis