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Githyanki
2014-Jun-20, 06:17 PM
It is possible to be so far away, that you can actually observe the Big-Bang? If so, are we that far away and is it possible scientists might discover it. If they do, what magnitude would it be at.

NEOWatcher
2014-Jun-20, 06:40 PM
By "observe" I assume you mean detect and not "see". It would be so far redshifted. In fact, it would probably redshift all the way to zero at the point of the big bang.
But; the state of the universe when it was a plasma (http://en.wikipedia.org/wiki/Recombination_(cosmology)) prevents it.

Noclevername
2014-Jun-20, 06:50 PM
We can already observe it, as the Cosmic Microwave Background.

NEOWatcher
2014-Jun-20, 06:54 PM
We can already observe it, as the Cosmic Microwave Background.
That's the point of decoupling (or last scattering) at about 379,000 years old. Not the beginning of the universe.

Noclevername
2014-Jun-20, 06:58 PM
That's the point of decoupling (or last scattering) at about 379,000 years old. Not the beginning of the universe.

:doh: You'd think being on an astronomy forum, I'd have known that by now. But no, this the first I've heard of it.

antoniseb
2014-Jun-20, 07:43 PM
What do you mean by Big Bang? Are you talking about the universal expansion that continues today? Or perhaps the end of inflation? or perhaps you mean whatever cause the expansion to begin in the first place? It gets trickier the further back you go... though I'd have to say your premise about distance shows a basic misunderstanding.

cjameshuff
2014-Jun-20, 09:32 PM
It is possible to be so far away, that you can actually observe the Big-Bang? If so, are we that far away and is it possible scientists might discover it. If they do, what magnitude would it be at.

As antoniseb said, your question shows a basic misunderstanding. The Big Bang wasn't an event that happened at some particular location, it's not meaningful to talk about distance from it.

Jeff Root
2014-Jun-20, 09:51 PM
What responders to Githyanki's questions should be doing is
explaining *where* the Big Bang took place and how it is that
we can see the light that was emitted as a consequence of the
Big Bang a few hundred thousand years later. That would take
care of his misunderstanding and answer the questions.

I'll try to do that in my next post, but I expect someone else
to post something better than I can, before I can.

-- Jeff, in Minneapolis

Jeff Root
2014-Jun-20, 10:49 PM
What we observe is light from stars and other hot gas.
The farther away from us the light was emitted, the longer
it takes to reach us. Cosmological distances are conveniently
often expressed in terms of light travel time. Light from the
stars in some particular distant galaxy might have taken nine
billion years to reach us. Travelling for nine billion years at
the speed of light means the light travelled a distance of
nine billion light-years.

Looking at this light, astronomers found that it is redshifted,
implying that the light sources and we are moving away from
each other.

The more distant a light source is, the more redshifted it is.
That implies that the more distant a galaxy is, the faster our
galaxy and the other galaxy are moving away from each other.

We look all around and see that the galaxies are distributed
in pretty much the same way all over the sky. Which implies
that everyone sees pretty much the same as we see: The
farther away a galaxy is, the faster it is moving away from
the observer.

This means the entire Universe that we can see is expanding
more or less uniformly. There are local clumps of galaxies
that stick together by their mutual gravitational attraction,
but overall, galaxies everywere are moving away from all the
other galaxies. Everyone sees more distant galaxies moving
away from them faster than nearer galaxies.

It also means that the galaxies used to be closer together
than we see them now. Extrapolate far enough backward in
time, and we reach a point at which all the galaxies and the
matter that composes them had to be in the same place.
That point in time is referred to as T=0, the time of the
Big Bang.

In the early 1960's it was discovered that microwaves were
coming from everywhere in the sky. It was quickly realized
that the microwaves were the extremely redshifted light
emitted by hot hydrogen gas very early in the history of the
Universe. The hot hydrogen gas was all the matter in the
entire Universe, everywhere in the Universe. The light it
was emitting began travelling toward us when the hydrogen
cooled enough to become transparent. So we only see the
light emitted at the moment -- a few hundred years long --
when the light was being "turned off" by cooling. Before
that time, the hydrogen absorbed the light and emitted it
again. After that time, the emiited light kept on travelling
through space indefinitely. It would keep on travelling
forever unless it happened to run into something like a
planet, which formed far away from and long after the
place and time where the light was emitted.

This light is the cosmic microwave background radiation,
or CMBR. It was visible light when it was emitted, with
a spectrum very much like that of a tungsten light bulb.
About half the temperature of the Sun's visible surface.
The expansion between the emission of that light and
observers now is a factor of about 1100 -- so great that
it has been redshifted all the way to the microwave part
of the spectrum.

Any event which occurred before the moment when the
hydrogen cooled enough to become transparent is hidden
behind the hydrogen. All light from such early times was
absorbed by the hot hydrogen. Its energy was eventually
released when the hydrogen became transparent.

-- Jeff, in Minneapolis

Cougar
2014-Jun-21, 12:33 PM
There are probably a number of nitpicks here, and I understand you're simplifying some of this, but I'll just pick one:


It was quickly realized
that the microwaves were the extremely redshifted light
emitted by hot hydrogen gas very early in the history of the
Universe.

This is a bit misleading. As the early universe was expanding, it was cooling. There were protons, neutrons, electrons and photons (and yes, neutrinos). Before it was cool enough for the protons to capture the electrons and hold onto them, forming hydrogen atoms, there were already about a billion photons per baryon. They weren't being emitted by "hydrogen gas." They were being scattered by the protons and electrons, which due to their plus or minus charges, affected the photons. But when the hydrogen (and helium) atoms formed at about 380,000 years after the beginning, the atoms are electromagnetically neutral. So the photons were no longer scattered, and could stream through the universe unimpeded.

JohnD
2014-Jun-21, 02:29 PM
It's difficult isn't it, Githyanki?

But be assured, philosophers have had the same problem from long before anyone thought of the Big Bang.
St.Augustine did in about CE 400:

"Chapter XII.—What God Did Before the Creation of the World.

14. Behold, I answer to him who asks, “What was God doing before He made heaven and earth?” I answer not, as a certain person is reported to have done facetiously (avoiding the pressure of the question), “He was preparing hell,” saith he, “for those who pry into mysteries.” It is one thing to perceive, another to laugh,—these things I answer not. For more willingly would I have answered, “I know not what I know not,” than that I should make him a laughing-stock who asketh deep things, and gain praise as one who answereth false things."

The Saint argued that even his god had to start somewhere, but that before then there was nowhere.

JOhn

Cougar
2014-Jun-22, 10:48 PM
It is possible to be so far away, that you can actually observe the Big-Bang?

As mentioned, no, you'll never be able to "see" earlier than the 380,000 year point. Space was essentially opaque to electromagnetic radiation before then. However, in the distant future, we should be able to "detect" very near the beginning, near the first second, perhaps, through the detection of primordial gravitational waves emanating from that time. We've already detected the imprint of those early gravitational waves, as manifest in the observed B-mode polarization of the CMB.

Reality Check
2014-Jun-22, 11:09 PM
We might also get closer to the Big Bang (t = 2 seconds) by measuring the cosmic neutrino background (http://en.wikipedia.org/wiki/Cosmic_neutrino_background) but that will be extremely difficult.

ShinAce
2014-Jun-23, 01:13 AM
To my knowledge, it is not possible to observe the big bang. It is a singularity, and there are two types of singularities. Falling into a black hole represents a singularity in the future. The big bang is a singularity in the past.

Which is to say, we can't possibly observe it because we are in it. We cannot get outside of it to watch it.

Jeff Root
2014-Jun-23, 01:39 AM
While I don't necessarily disagree with either assertion on its
own, you put two assertions together in one short post which
contradict each other. If the Big Bang is a singularity, then we
cannot be in it. If we are in it, then it cannot be a singularity.

From what we can see of the aftermath of the Big Bang, it
appears to have begun in a singularity. But appearances can
be deceiving.

-- Jeff, in Minneapolis

.

Noclevername
2014-Jun-23, 04:16 AM
Anywhere or when you could observe the Big Bang, you'd have to be in it. It was the state of the whole universe, after all.

WayneFrancis
2014-Jun-23, 04:26 AM
Saying the universe started as a singularity I think is going way beyond what the current data says. Even at T0 the visible universe could have had a non zero volume. Even in the multi-verse theories I'm not sure what the current models predict with a new universe with regard to the bubble. I'm still not sure if these theories have any issue with a new universe being infinite in size, at their beginning, either.

Noclevername
2014-Jun-23, 04:34 AM
Saying the universe started as a singularity I think is going way beyond what the current data says. Even at T0 the visible universe could have had a non zero volume. Even in the multi-verse theories I'm not sure what the current models predict with a new universe with regard to the bubble. I'm still not sure if these theories have any issue with a new universe being infinite in size, at their beginning, either.

Singularity, as far as I understand it, means that a specific situation is beyond our ability to mathematically model. It's a placemark for a "Here Be Dragons" in physics terms, not a specific physical state.

Jeff Root
2014-Jun-23, 05:08 AM
That isn't what Penrose and Hawking meant by "singularity".

A singularity is a place where some values go to zero and
some values become infinite or undefined. Hawking found
that GR predicts the density of the Universe to have been
infinite at a time in the past, defining T=0. That would be
a singularity. The GR calculation does not take quantum
mechanics into consideration, so it isn't known whether the
Universe actually started in a singularity or not.

-- Jeff, in Minneapolis

ShinAce
2014-Jun-23, 11:11 PM
That doesn't change the fact that regression shows a singularity at t=0, and we are in it. Arguing that it isn't a real singularity does not address the OP.
The other singularity you often hear about(black hole) is one we are not inside.
Semantics aside, how do you plan on observing the big bang?

Also, the CMBR only blocks photons. In theory, we could still see neutrinos beyond the surface of last scattering. Plus there's the recent result from BICEP2 that argues for gravitational waves being imprinted on the distant horizon, which would have as its cause an event before that.

effingham
2014-Jul-14, 05:10 AM
That doesn't change the fact that regression shows a singularity at t=0, and we are in it.

Regression of what shows this?

Jeff Root
2014-Jul-14, 03:20 PM
By "regression" he meant extrapolation backward in time.
We see galaxies moving apart at a rate which varies with
distance in a certain way. Regressing the history shows
that all the galaxies would have been smushed together
about 13.7 billion years ago.

Obviously we aren't in the singularity at t=0, but I'm sure
ShinAce has some more-or-less rational reason for saying
"we are in it". Most likely it makes perfect mathematical
sense but has no physical significance.

-- Jeff, in Minneapolis

primummobile
2014-Jul-14, 03:34 PM
Obviously we aren't in the singularity at t=0, but I'm sure
ShinAce has some more-or-less rational reason for saying
"we are in it". Most likely it makes perfect mathematical
sense but has no physical significance.

-- Jeff, in Minneapolis

He said it because when you extrapolate back to the "singularity", there is no where else for "us" or anyone else to be other than "inside" of it. Not liking the semantics of what he said doesn't make it untrue. Do you know of anything in the universe that wasn't once inside of the hot, dense state at the beginning? Neither do I. That's why "we" couldn't observe it. To observe something usually implies not being a part of it.

effingham
2014-Jul-14, 03:38 PM
By "regression" he meant extrapolation backward in time.
We see galaxies moving apart at a rate which varies with
distance in a certain way. Regressing the history shows
that all the galaxies would have been smushed together
about 13.7 billion years ago.

Obviously we aren't in the singularity at t=0, but I'm sure
ShinAce has some more-or-less rational reason for saying
"we are in it". Most likely it makes perfect mathematical
sense but has no physical significance.

-- Jeff, in Minneapolis

Your belief is erroneous. Not all galaxies are moving apart, some are moving toward each other. You can not simply "extrapolate backward" from that and conclude everything was once all together. Well, you can, but it defies all reason and logic, especially when that extrapolation is used to prop up an absurd creation myth like "big bang".

effingham
2014-Jul-14, 04:05 PM
Do you know of anything in the universe that wasn't once inside of the hot, dense state at the beginning?

There is as yet no evidence that the universe ever had a beginning.

Cougar
2014-Jul-14, 04:36 PM
There is as yet no evidence that the universe ever had a beginning.

In order to make this claim, you have to willfully ignore at least six independent lines of evidence that point to the conclusion that our observable universe did indeed have a beginning.

Jeff Root
2014-Jul-14, 05:41 PM
He said it because when you extrapolate back to the
"singularity", there is no where else for "us" or anyone
else to be other than "inside" of it.
But we aren't at t=0. That was over 13 billion years ago.
The singularity, if any, was a point in time -- the beginning
of time -- more than 13 billion years ago. It doesn't exist
any more, so we aren't in it. Obviously. Very obviously.

We are in the Universe that came from the Big Bang.
But the singularity is no more, and we aren't in it.



Not liking the semantics of what he said doesn't make it
untrue.
I can only understand what he said if I understand the
meanings of the terms he used. I understand why the
Universe was inferred to have begun at a singularity.
It follows naturally from observations of the CMBR and
galaxies, and general relativity. We are not in that
singularity, because it no longer exists, if it ever did.

-- Jeff, in Minneapolis

Jeff Root
2014-Jul-14, 06:02 PM
Not all galaxies are moving apart, some are moving
toward each other.
As I said in post #9, local clumps of galaxies stick
together by their mutual gravitational attraction. Out
of all the galaxies that have been observed so far, less
than a dozen of the very nearest galaxies are moving
closer to us rather than farther away. The more distant
a galaxy is, the faster it is moving away. The pattern is
entirely clear and unambiguous.

In general, an observer anywhere in the Universe would
see pretty much the same thing: Just a handfull of nearby
galaxies are not moving away. More distant galaxies are
moving away at speeds proportional to their distance.



You can not simply "extrapolate backward" from that and
conclude everything was once all together. Well, you can, ...
Yes, I can, and it works just fine. We don't know how or
why the Big Bang occurred, but we can say for certain that
everything in the Universe is coasting apart from a time
when it was all much closer together and much hotter.

-- Jeff, in Minneapolis

primummobile
2014-Jul-14, 06:06 PM
But we aren't at t=0. That was over 13 billion years ago.
The singularity, if any, was a point in time -- the beginning
of time -- more than 13 billion years ago. It doesn't exist
any more, so we aren't in it. Obviously. Very obviously.

We are in the Universe that came from the Big Bang.
But the singularity is no more, and we aren't in it.


I can only understand what he said if I understand the
meanings of the terms he used. I understand why the
Universe was inferred to have begun at a singularity.
It follows naturally from observations of the CMBR and
galaxies, and general relativity. We are not in that
singularity, because it no longer exists, if it ever did.

-- Jeff, in Minneapolis


When we "extrapolate", we are taking a metaphorical clock and running it either backward or forward and observing what our model(s) says will happen. To literally "witness" the big bang, you would have to literally be there at zero time in order to witness it. Unfortunately for us, zero time is inside the "singularity", which is the bit of hyperbole Shinace is using. Our only theory says it was a singularity. The fact that we think the singularity part is wrong doesn't make it difficult to understand what he is saying. What he is saying is that when you run the clock backwards to the big bang, there is no such thing as "outside". Consequently, we cannot observe it.

Now, run the clock to the present date. He is arguing that because of our origin, we cannot observe what effects there would have been at zero time. Because at that time any effects would have necessarily taken place outside of the universe, which is impossible for us to observe.

"Inside the singularity" is a rhetorical device that he is using to make a point. You frequently use, and I believe correctly use, less than precise descriptions to describe things to people in lay terms. Shinace is doing the same thing. You don't even seem to be trying to understand his point. He makes an interesting point that could be argued and discussed but unfortunately it won't be because in every discussion someone always has to have some niggling semantic distinction that they have to make and we can't ever talk until everyone is past it. So to get past it, just substitute "universe" for where he said "singularity" in his posts. Since he said our entire universe is the "singularity" (in other words it was all once in there) then it can be safe bet that "universe" is a good word to use instead.

ShinAce
2014-Jul-14, 08:54 PM
"Inside the singularity" is a rhetorical device that he is using to make a point. You frequently use, and I believe correctly use, less than precise descriptions to describe things to people in lay terms. Shinace is doing the same thing. You don't even seem to be trying to understand his point. He makes an interesting point that could be argued and discussed but unfortunately it won't be because in every discussion someone always has to have some niggling semantic distinction that they have to make and we can't ever talk until everyone is past it. So to get past it, just substitute "universe" for where he said "singularity" in his posts. Since he said our entire universe is the "singularity" (in other words it was all once in there) then it can be safe bet that "universe" is a good word to use instead.

Exactly!

We are in the universe. The universe shows a singularity at t=0. We live in a universe which shows a singular point.

Depending on the coordinates you use, the event horizon of a black hole shows a singularity. Jeff: Are you saying that since it is impossible to be in a singularity, it is impossible to be inside an event horizon? You definitely can fall into a black hole, but once you do, you can't get out. You can't get out of a black hole in the same sense that you can't get out of a universe.

The only difference between these two scenarios is that the singularity of the black hole can 'catch' us in the future. The singularity of the universe caught us long ago. You can witness the formation of a black hole. You cannot witness the big bang, no matter how hard you try.

It's like trying to witness the birth of your parents, in person.

Jeff Root
2014-Jul-14, 10:28 PM
We are in the universe. The universe shows a singularity
at t=0. We live in a universe which shows a singular point.
None of which I disagreed with.



Depending on the coordinates you use, the event horizon
of a black hole shows a singularity. Jeff: Are you saying
that since it is impossible to be in a singularity, it is
impossible to be inside an event horizon?
I did not say that it is impossible to be inside a singularity.
I do not know whether it is possible or not, and I don't have
a definite opinion on it.

I said nothing about any event horizon.

I implied nothing about any event horizon.

Even if the premise is true, the relation you suggest is
obviously bunk.

What I said was completely clear and very simple: The
Universe may have begun at a singularity which was the
beginning of time. That was some 13.7 billion years ago,
not now. The singularity no longer exists. We exist now.
So we are not "in" that particular singularity.



You definitely can fall into a black hole, but once you do,
you can't get out. You can't get out of a black hole in the
same sense that you can't get out of a universe.

The only difference between these two scenarios is that the
singularity of the black hole can 'catch' us in the future. The
singularity of the universe caught us long ago. You can
witness the formation of a black hole. You cannot witness
the big bang, no matter how hard you try.

It's like trying to witness the birth of your parents, in person.
Every event that is ever witnessed occurred in the past.
It may be the very recent past or the very far past.

Whether the Big Bang can be witnessed depends only on
whether some kind of record of it exists and is accessible.
My ability to witness the trees outside my window depends
on the record formed by the sunlight reflecting off of them
and travelling to my eyes. Is there a comparable record of
the Big Bang? I don't know. I'm pretty sure you don't
know either.

I didn't claim that it is possible to see the Big Bang, and I
didn't claim that it isn't possible, so I have no idea why you
are saying these things in a reply to me.

-- Jeff, in Minneapolis

Jeff Root
2014-Jul-15, 12:32 AM
ShinAce,



I did not say that it is impossible to be inside a singularity.
I do not know whether it is possible or not, and I don't have
a definite opinion on it.
I see that this must be what you were referring to:



If the Big Bang is a singularity, then we cannot be in it.
If we are in it, then it cannot be a singularity.
We cannot be in the Big Bang singularity because that
singularity is a point in time in the distant past. If the
singularity were a continuing thing, then we could be
"in" it.

-- Jeff, in Minneapolis

Jeff Root
2014-Jul-15, 12:50 AM
I didn't claim that it is possible to see the Big Bang, and I
didn't claim that it isn't possible, so I have no idea why you
are saying these things in a reply to me.
Okay, so in post #9 I did say we can't see the Big Bang,
but as Cougar noted, it was a deliberate simplification.
We can see -- in microwaves -- as far back as a few
hundred thousand years after the Big Bang. We might
be able to see much closer with something other than
photons. Eventually we might get records of observations
made by others over a period of billions of years that would
help us see very far back. Along with their interpretations
of those observations. If there is a functioning library
somewhere nearby....

-- Jeff, in Minneapolis

.

primummobile
2014-Jul-15, 01:14 AM
None of which I disagreed with.


I did not say that it is impossible to be inside a singularity.
I do not know whether it is possible or not, and I don't have
a definite opinion on it.

I said nothing about any event horizon.

I implied nothing about any event horizon.

Even if the premise is true, the relation you suggest is
obviously bunk.

What I said was completely clear and very simple: The
Universe may have begun at a singularity which was the
beginning of time. That was some 13.7 billion years ago,
not now. The singularity no longer exists. We exist now.
So we are not "in" that particular singularity.


"The universe may have begun as a universe which was at the beginning of time. That was some 13.7 billion years ago, not now. The universe no longer exists. We exist now. So we are not "in" that particular universe."

I don't exactly agree with the premise or how it is being stated. But it is a metaphor. A metaphor is not literal. We are not outside of our universe and nothing that we know of ever was. "Witnessing" something implies a causal connection that we don't have here without time travel. Detecting remnants of something is not witnessing.

WayneFrancis
2014-Jul-15, 01:47 AM
To my knowledge, it is not possible to observe the big bang. It is a singularity, and there are two types of singularities. Falling into a black hole represents a singularity in the future. The big bang is a singularity in the past.


Which is to say, we can't possibly observe it because we are in it. We cannot get outside of it to watch it.

BAH! just noticed that I already replied to this post, much in the same way, weeks ago. I need to look at dates of posts more. But here is today's reply to the same thing as I don't believe in deleting posts even seconds after making them.


------------------------------------------------------------------------

I'll point out that we don't even know if it was a "singularity". Our physics breaks down before that point. T=0 doesn't necessarily mean an infinitely small point and the beginning of time. The "universe" could be infinite in size at what we call T=0 and it could have been around for an infinite amount of time at T=0. We just don't know. The "singularity" is a over simplification of extrapolating back the expansion and inflation of the visible universe. What happens at T=0 will require new models because our current models can not get back that far so T=0 is a lot of speculation. Just my nitpick :)

WayneFrancis
2014-Jul-15, 02:26 AM
I'm sure someone will correct me if I get something wrong here.
The "singularity" is more of a pop-sci description of extrapolating the expansion and inflation backwards in time.
There are various hypothesis on the start of the universe that have the beginning as a "Hot dense state" of some volume either infinite or finite. There may be some hypothesis where the universe started as a region of spacetime of zero volume. In either case our current models break down before we get to T=0. Until we get a well developed theory of quantum gravity we probably won't know what happen in those "first moments". The T=0 is just a convenient starting point. Just like a road race has a start line the road often extends well behind the stop line.

So saying that the start of the curvature of spacetime for our observable universe was infinite is extrapolating back further then our models support and most cosmologists I've heard describe the early universe make it clear we don't know what happened at that point in time and they have formed a ton of hypotheses to get around that problem.

I've heard a good description of the cosmic singularity before and it goes something like this.


The big bang singularity is just an artefact that needs to be replaced by a more accurate description/ model. Perhaps when quantum gravity research has made suitable progress we may be able to give a better description of what happened at T=0 and perhaps even shift were T=0 represents


So my OCD here is the use "singularity" because to many people they'll think "Black hole" and not "our models break down". Partly because that is what they are used to and partly because the pop-sci description describes the early universe in terms that make it sound like scientist know, and even say more, then they actually do.

Personally I've come a long way in my understanding of the current theories and hypotheses of the early universe do to the other great members here at these forums mostly.

primummobile
2014-Jul-15, 02:31 AM
I think everyone has made it clear that "singularity" is, at best, a placeholder for some unknown that is the reality.

It's not pop sci that tells us the universe started with a singularity. It is GR. We assume that infinite results in GR mean that the theory is incomplete.

ShinAce
2014-Jul-15, 03:29 AM
There is another thread which is focused on whether or not our universe emerged from actual singularity or something else:
http://cosmoquest.org/forum/showthread.php?152209-How-Do-We-Know-(Big-Bang-Initial-Size)

There are, of course, many definitions of a singularity. In calculus, we saw a singularity as a point where a function is not smooth. It can also mean an undefined or indeterminate point.

In physics, it is used as a placeholder for places where the theory no longer gives defined values.

In cosmology, it is used to mean the cosmic singularity(the big bang) or sometimes the center of a black hole. There's even a naked singularity.

At any rate, the answer to the original question is: No, you cannot witness the big bang, unless you have a unique definition of witness.

WayneFrancis
2014-Jul-15, 05:40 AM
I think everyone has made it clear that "singularity" is, at best, a placeholder for some unknown that is the reality.

It's not pop sci that tells us the universe started with a singularity. It is GR. We assume that infinite results in GR mean that the theory is incomplete.

Exactly my point. GR breaks down thus most cosmologist won't talk about T=0 as as singularity like we do a black hole. Despite the fact that when you talk/listen to most cosmologist they make it clear that our models, including GR, break down before all of the observable universe would be in a region of zero volume you still see pop sci talk about the start of the universe as being infinitely small. High energy physicists can get us to a point where the observable universe is smaller then an atom but still not a zero volume and even then there is suspected to be much more around that region. Just that it is now outside our Hubble sphere.

Bah...like I said I get OCD about this topic.

primummobile
2014-Jul-15, 12:14 PM
Exactly my point. GR breaks down thus most cosmologist won't talk about T=0 as as singularity like we do a black hole. Despite the fact that when you talk/listen to most cosmologist they make it clear that our models, including GR, break down before all of the observable universe would be in a region of zero volume you still see pop sci talk about the start of the universe as being infinitely small. High energy physicists can get us to a point where the observable universe is smaller then an atom but still not a zero volume and even then there is suspected to be much more around that region. Just that it is now outside our Hubble sphere.

Bah...like I said I get OCD about this topic.

Yes, I misunderstood you a bit. I agree with this. Personally, I don't even like talk of a singularity in a black hole. But I think it's okay if used as a placeholder as long as everyone understands that it means we really have no idea what is going on there. You're correct that popular science articles blur the line.

Jeff Root
2014-Jul-15, 01:24 PM
You guys seem to be agreeing with Wayne when he claims that
GR "breaks down" even before regressing the extrapolation all
the way to t=0. I see no support for that assertion. GR does
not "break down". It happily predicts infinite density at t=0
without even a hiccup. The problem comes when the rest of
physics is taken into consideration. GR knows nothing about
particles. As far as GR is concerned, there is no such thing as
a particle. QM deals with particles, but can't handle the very
high density predicted by GR when nearing the singularity of
the Big Bang. So although it is entirely possible that GR has
a problem, it is also entirely possible that it does not.

On the other hand, we can be completely certain that QM is
incomplete. QM needs to be extended to explain what went
on at the very beginning of the Universe. That extension,
whatever it might consist of, could be all that is needed to
eliminate the conflict between QM and GR. It would also
probably either eliminate the singularity predicted by GR or
change the conditions near and at the singularity such that
it would no longer be a problem for QM.

-- Jeff, in Minneapolis

primummobile
2014-Jul-15, 01:27 PM
You guys seem to be agreeing with Wayne when he claims that
GR "breaks down" even before regressing the extrapolation all
the way to t=0. I see no support for that assertion. GR does
not "break down". It happily predicts infinite density at t=0
without even a hiccup. The problem comes when the rest of
physics is taken into consideration. GR knows nothing about
particles. As far as GR is concerned, there is no such thing as
a particle. QM deals with particles, but can't handle the very
high density predicted by GR when nearing the singularity of
the Big Bang. So although it is entirely possible that GR has
a problem, it is also entirely possible that it does not.

On the other hand, we can be completely certain that QM is
incomplete. QM needs to be extended to explain what went
on at the very beginning of the Universe. That extension,
whatever it might consist of, could be all that is needed to
eliminate the conflict between QM and GR. It would also
probably either eliminate the singularity predicted by GR or
change the conditions near and at the singularity such that
it would no longer be a problem for QM.

-- Jeff, in Minneapolis

Semantics. GR breaks down as a predictive theory when it gets into that realm, and every physicist on the planet agrees with that. I said above It's not pop sci that tells us the universe started with a singularity. It is GR. We assume that infinite results in GR mean that the theory is incomplete. Everyone agrees that GR happily predicts a singularity and everyone agrees that because of this our theory of what happens in the center of a black hole or at t=0 must be incomplete since QM doesn't currently allow it.

Jeff Root
2014-Jul-15, 02:03 PM
So explain to me how "GR breaks down". I say that it
works perfectly. It isn't the fault of GR that it gives
apparently impossible results when the input values
ignore QM limitations.

You have no reason to assume that the infinite results
in GR mean that GR is incomplete. It is QM that is
incomplete. GR might be incomplete, but there is no
evidence that it is.

Beyond that, you have no reason to assume that the
infinite results in GR were not the actual values at t=0.
I expect that changes / additions to QM will show how
they weren't infinite, but with what we know currently,
it is still possible that the values *were* infinite.

We *know* that QM has to be extended. We *don't*
know that GR has to change in any way. Even if GR
gives incorrect results, if it does so because QM isn't
applied correctly, then it is not GR's fault.

-- Jeff, in Minneapolis

primummobile
2014-Jul-15, 02:09 PM
There most certainly is evidence that GR is incomplete. The fact that it disagrees with a model that has been verified to orders of magnitude greater accuracy is the main evidence.

Regardless, I didn't say GR is incomplete. I said that we assume it is incomplete. And the reason is the reason I gave above. And that reason is why physicists have spent decades searching for a model to unify QM with GR. You said "I expect that changes / additions to QM will show how
they weren't infinite" There is absolutely no difference between saying "I expect" and "I assume". You could have just as easily substituted "I assume" in that statement and it would have meant exactly the same thing. So you are arguing with yourself.

The only thing I or anyone else is saying with certainty is that our model of what happens at the center of a black hole or at t=0 is incomplete. And it is. Whether that means there is a singularity or not doesn't have anything to do with the fact that it is incomplete.

An outcome isn't a theory's "fault". I love GR. But that doesn't mean that doesn't mean that GR correctly models the inside of a black hole because all the evidence we have seems to indicate that for those scales some other effect is more dominant. The expansion of the universe is a main driving force in what we see when we look at the sky. But our local group overcomes that expansion in relation to one another. That doesn't mean expansion is wrong. It means that there are other, more locally dominant, factors at play.

Jeff Root
2014-Jul-15, 03:44 PM
There most certainly is evidence that GR is incomplete.
The fact that it disagrees with a model that has been
verified to orders of magnitude greater accuracy is the
main evidence.
I think this is more likely a misinterpretation of the
implications of the disagreement. What model and what
disagreement do you have in mind?

Aspects of QM have certainly been verified to orders of
magnitude greater accuracy than GR, but only within a
limited range of densities. It seems entirely likely that
GR would apply regardless of the density, while QM must
change radically to accurately describe the behavior of
particles at densities ten or twenty orders of magnitude
greater than anything ever tested.



Regardless, I didn't say GR is incomplete. I said that we
assume it is incomplete. And the reason is the reason
I gave above.
And I say there is no good reason to assume that GR is
incomplete. We know that QM is incomplete. GR might
be incomplete, too, but there is no evidence that it is.
Additions or changes to QM could eliminate the conflict
between QM and GR. We can assume that either QM or
GR or both must be extended or changed, but since we
know for sure that QM must be extended or changed,
there is no reason to assume that GR must be, too.



And that reason is why physicists have spent decades
searching for a model to unify QM with GR. You said
"I expect that changes / additions to QM will show how
they weren't infinite" There is absolutely no difference
between saying "I expect" and "I assume". You could
have just as easily substituted "I assume" in that
statement and it would have meant exactly the
same thing. So you are arguing with yourself.
Expecting something and assuming it are quite different.
I expect that my checking account has enough money to
cover my purchases today, but I don't just assume that
it does and then see what happens when I buy a bunch
of stuff.

I expect that changes to QM will allow QM and GR to be
unified, but I don't assume it. Unification might require
changes to GR, too. I think that is unlikely, but it is
certainly possible.



An outcome isn't a theory's "fault".
It is if the outcome is wrong because the theory is wrong.

It is not the theory's "fault" if if the outcome is wrong
because wrong data was input to the theory.



I love GR. But that doesn't mean that doesn't mean that
GR correctly models the inside of a black hole because all
the evidence we have seems to indicate that for those
scales some other effect is more dominant.
I disagree. The evidence we have so far seems to
indicate that gravity completely overwhelms quantum
effects in that situation, to the extent that QM effects
vanish.

I like your analogy with cosmic expansion, but I think it
does not accurately analogize to what happens inside a
black hole. No force can resist the crush of collapsing
matter due to the unimaginably strong gravity, so QM
apparently becomes irrelevant. That might not be what
actually happens, but at the current state of knowledge,
it appears to be what happens.

-- Jeff, in Minneapolis

primummobile
2014-Jul-15, 03:58 PM
Regular old classical mechanics can describe a black hole. In fact, the possibility of a black hole was described in the 1700s.

Using GR, the Schwarzschild Radius of the sun is about 3km. That is small, but it is not a point. We have evidence of stars even more dense than neutron stars that are not black holes. QM forbids particles from occupying a space smaller than their wavelengths. I don't know of any evidence that says gravity overcomes this.

Again, no one is saying that there isn't a singularity. And no one is saying that there is. Whether or not one leans one way or another is immaterial. The fact that we are pretty sure that we don't know what is at the center of a black hole means that something about our way of thinking about it is incomplete. GR predicts black holes. That's why we assume that end of it is incomplete, because we don't have any other theory of gravity. If we even had a quantum gravity theory then we could say it is incomplete.

Most people don't like singularities because infinities usually mean an error in the math. I'm not saying they always mean an error. I'm saying usually. You're reading much more into this than you should be.

PetersCreek
2014-Jul-15, 05:01 PM
Thread moved to the Astronomy forum for protracted discussion.

effingham
2014-Jul-17, 10:22 PM
In order to make this claim, you have to willfully ignore at least six independent lines of evidence that point to the conclusion that our observable universe did indeed have a beginning.
If you think there is evidence suggesting the universe had an origin, present it here or all else becomes moot. Are you including the genesis myth from the bible?

effingham
2014-Jul-17, 10:32 PM
As I said in post #9, local clumps of galaxies stick
together by their mutual gravitational attraction.

The gravitational attraction between the sun and its nearest neighbor is comparable to that between two grains of sand four miles apart. That between two galaxies would be comparable to that between a sandbox on earth and a sandbox on the moon. To suggest "gravity" is the binding force in the universe ignores a century of plasma cosmology.

Your belief that "redshift" indicates either distance or velocity is spurious.