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mdpalow
2014-Jul-09, 11:53 AM
How do we know the big bang originated from something the size of a singularity and not from something the size of our moon or our planet for example.

I heard the explanation once a long time ago, but can't remember from where or how it was known.

Looking forward to your answer.

Thanks!

Swift
2014-Jul-09, 02:19 PM
Hi mdpalow, welcome to CQ.

I've moved your thread from Astronomy to Q&A; I think you'll get a response faster here.

Shaula
2014-Jul-09, 02:28 PM
Short answer: We don't.
Edit: That is to say we don't know it came from a singularity

Our models only run back to about a million-millionth of a second prior to the point where a singularity would be if you just extrapolate back (we know that this extrapolation is not valid because we know our current theories of physics break before this point). At that point the entire observable universe was (from memory) of the order of metres across.

So the things to bear in mind are that the current models don't say much about anything outside the observable universe. We suspect it is like what we see around us but we don't know - because we don't know how big the entire universe is. Also the singularity is not actually part of the current models. You get one by extrapolating back beyond the point at which we know they are not applicable.

WayneFrancis
2014-Jul-10, 06:05 AM
I can't add much to what Shaula said but that I thought the size of the observable universe was much smaller. At first thought one way to look at it is that at 10−37 the observable universe could be no bigger then the distance light can travel in 10−37s. A proton is ~10−15m. Light speed is ~3x108...if I wasn't up all night with a massive tooth ache I might actually get the fairly straightforward math right in my head. But now that I think about it ... this is all dependent on opposite sides of the observable universe being at thermal equilibrium. Which if it was the size it was for a long time wouldn't be an issue either. Either way I thought the observable universe was on the size of a proton back then.

Shaula
2014-Jul-10, 06:34 AM
I am taking the end of inflation as the point where we have sufficient confidence that we can predict a size - current models of inflation only put bounds on how much of an effect it could have had rather than giving us exact numbers. Hopefully when/if we pin down a mechanism for it we'll get better numbers out. So I was going from about 10e-32s (when the observable universe was between the size of a grapefruit and a beachball).

WayneFrancis
2014-Jul-10, 11:39 PM
Ah got you.

effingham
2014-Jul-14, 04:58 AM
How do we know the big bang originated from something the size of a singularity and not from something the size of our moon or our planet for example.

I heard the explanation once a long time ago, but can't remember from where or how it was known.

Looking forward to your answer.

Thanks!
We don't know that "big bang" even happened

Cougar
2014-Jul-14, 12:13 PM
...something the size of a singularity...

Besides, a singularity is not a thing. It's a point where the mathematics - in this case, the mathematics of general relativity - become undefined, or inapplicable, or incomplete. That's because quantum processes become very significant at such an early stage of the universe's evolution, and general relativity does not incorporate quantum processes.

Further, to talk about size, you have to define a metric, i.e., a way to measure size. This is not so clear cut when considering the state of the universe so close to the beginning.

Swift
2014-Jul-14, 01:21 PM
We don't know that "big bang" even happened
effingham,

Do not advocate non-mainstream positions in Q&A. Q&A is only for mainstream answers.

If you have not reviewed our rules (link in my signature), I suggest you do so soon.

Strange
2014-Jul-14, 03:00 PM
We don't know that "big bang" even happened

We know that the "big bang" in the sense of the universe expanding from an earlier hot, dense state happened - and is still happening. That is what the term origianlly described.

Since then the popular press and some science writers have used it to refer to some sort of "creation event"; it is probably true that we don't know if such a thing happened or not.

Jeff Root
2014-Jul-14, 08:54 PM
Relatively minor disagreements with Shaula and Wayne:

General relativity plus the observation that galaxies are
moving apart unambiguously predicts a singularity. That
singularity was the beginning of the Universe. GR has no
problem with that, all the way back to t=0.

It so happens that close to the singularity, the energy
density approaches infinite. At t=0 it would have been
infinite. Neither of those fits in with the known laws of
quantum mechanics. So either there was no singularity,
or the laws of QM need to be added to, or GM needs to
be revised, or some combination of the above.

I think it is clear that QM has to be extended in order to
account for the Big Bang. That could result in elimination
of the singularity without any change to GR. Or it could
simply alter the conditions near the singularity such that
the density did not approach infinite.

-- Jeff, in Minneapolis

Thanatos
2014-Jul-17, 05:08 AM
The big bang was more a point in time than space. It could have been any size, including infinite. It is problematic to dimensionalize the big bang. We know, for example, the surface of last scattering appeared about 400,000 years after the BB, but, cannot assign it a size - only a scale factor relative to 'today'. We would need to know the entire expansion history of the universe, which is unknown, to even make an approximation.

WayneFrancis
2014-Jul-18, 05:04 AM
How do we know the big bang originated from something the size of a singularity and not from something the size of our moon or our planet for example.

I heard the explanation once a long time ago, but can't remember from where or how it was known.

Looking forward to your answer.

Thanks!
Bah didn't notice this was an old post...that I already replied to.

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

We don't. In fact saying the big bang started from a size of zero volume is not really science. It is a pop sci answer that extrapolate further back then the models allow. The observable universe started out very small and we can calculate that back with high energy physics to smaller then a proton but there is a point before that were our models break down.

The big bang assumes as non zero volume of space to begin with. Until we get a proper quantum theory of gravity we probably won't be able to say much on what happened before the point where our current models fail.
Now the why was the observable universe smaller then a proton and not the size of the moon? I believe the answer to that lies more in that there is no reason it should stop at the size of the moon. Our current theories work many orders of magnitude beyond that size. The trick seemed to be how did the early universe get big enough that it didn't immediately crunch back down on itself and that seem to because the initial inflation was fast enough to get over that limit.

WayneFrancis
2014-Jul-18, 05:08 AM
We don't know that "big bang" even happened

We do know that it happened. We have multiple lines of evidence that it happened. If it didn't happen we wouldn't be here :P
Seriously the Big Bang is the best explanation for the observations we have and we have a ton of observations that all point to the same thing. That our observable universe was in a very hot dense state and that it had a rapid period of inflation...blah blah blah...current day cosmic expansion is not only happening but also increasing in its rate.

Reality Check
2014-Jul-21, 04:27 AM
GR has no
problem with that, all the way back to t=0.

We should emphasize that "back to t=0" does not include t=0 because that is where GR fails. Better stated as "back toward t=0".
Replace GR and QM with a new theory (quantum loop gravity, string theory, etc.) that incudes them and the expectation is that the singularity goes away. Of course quantum field theories have plenty of singularities of their own (see renormalization (http://en.wikipedia.org/wiki/Renormalization)).
But this is not GR or for that matter QM. The singularity remains in GR.

Jeff Root
2014-Jul-21, 07:08 AM
I still don't see any evidence that GR fails at t=0. That
has been asserted many times by many posters here on
CosmoQuest, but almost nowhere else.

As far as I can see, GR works just fine all the way back to
t=0, as I said. The problem arises only when other physics
is applied -- namely quantum mechanics. GR predicts infinite
density at t=0, which QM can't handle. QM can't handle
extremely high densities shortly after t=0, either, so the
actual conditions shortly after t=0 can't be modelled with
current theory.

The prediction by GR of a singularity at t=0 was possible
because GR *does* work all the way back to t=0. If it
failed, it would not be able to predict the singularity.

And to be boringly repetative, that doesn't mean there was
a singularity at t=0 or that the density was infinite -- it just
means that QM isn't complete.

-- Jeff, in Minneapolis

Strange
2014-Jul-21, 07:13 AM
I still don't see any evidence that GR fails at t=0. That
has been asserted many times by many posters here on
CosmoQuest, but almost nowhere else.

A quick check on Arxiv finds several papers saying the same thing.


If it failed, it would not be able to predict the singularity.

In what way is predicting something that almost certainly doesn't exist not a failure?


it just means that QM isn't complete.

While QM may not be complete, I assume you mean GR in this context?

Jeff Root
2014-Jul-21, 08:23 AM
No, as I've said maybe six or seven times in various different
threads, including previously in this one, I meant QM, not GR.

And as I've said several times, we know for sure that QM has
to be extended to account for whatever happened at the Big
Bang. As it stands now, it can't do that. Extending it in that
way might, for example, describe how all the matter-energy
of the Universe came into existence over a period of time
(maybe a second, or a picosecond), eliminating the infinite
density predicted by GR. No change needs to be made to GR
to change the result of GR's prediction. GR's prediction is
calculated with the assumption that the mass-energy of the
Universe doesn't change.

If I have an apple (which I do), and multiply the number of
apples I have by two every day, in less than two months I'll
have over a quintillion apples. Certainly that number of
apples doesn't exist in the whole world. Multiplication must
be incorrect, mustn't it? It failed by predicting an impossible
number of apples in a perfectly reasonable period of time.

Or maybe one of the inputs into the multiplication was wrong.
Maybe it wasn't a failure of multiplication, but a failure to
account for the fact that I can't increase the number of apples
I have in the way I assumed.

GR might be incomplete, like QM, but the fact that it predicts
a singularity and infinite density at t=0 is not a failure of GR.
It is a correct prediction by GR from the assumption that the
mass-energy of the Universe is unchanging.

-- Jeff, in Minneapolis

Strange
2014-Jul-21, 09:02 AM
GR might be incomplete, like QM, but the fact that it predicts
a singularity and infinite density at t=0 is not a failure of GR.

Well, if you don't think that dividing by zero is not a sign of failure, I don't know what is.

We probably need a theory of quantum gravity (an extension to GR, taking into account quantum-level effects) to properly describe black holes and the earliest times of the universe.


Extending it in that
way might, for example, describe how all the matter-energy
of the Universe came into existence over a period of time
(maybe a second, or a picosecond), eliminating the infinite
density predicted by GR.

Or maybe a theory of quantum gravity (an extension to GR) would not predict a singularity.

Cougar
2014-Jul-21, 11:43 AM
I still don't see any evidence that GR fails at t=0.... GR predicts infinite density at t=0....

Does "infinite density" make sense to you? :confused:

It is the prediction of infinite density, among other things, that demonstrates GR has gone off the tracks.

Strange
2014-Jul-21, 11:58 AM
And wouldn't it be more accurate to say that density is undefined, as it involves a division by zero?

Jeff Root
2014-Jul-21, 07:09 PM
GR might be incomplete, like QM, but the fact that it predicts
a singularity and infinite density at t=0 is not a failure of GR.
Well, if you don't think that dividing by zero is not a sign of
failure, I don't know what is.
This division by zero is essentially a division of the mass
of the Universe by the volume of the Universe. If the volume
was zero at the very beginning, then division by zero occurs
at that point.

It does not suggest any kind of failure.



We probably need a theory of quantum gravity (an extension
to GR, taking into account quantum-level effects) to properly
describe black holes and the earliest times of the universe.
Saying that we "probably" need a theory of quantum gravity
goes beyond what we know. We *might* need a theory of
quantum gravity. We *know* we need a more complete
quantum theory. That alone might suffice.




Extending it in that way might, for example, describe how
all the matter-energy of the Universe came into existence
over a period of time (maybe a second, or a picosecond),
eliminating the infinite density predicted by GR.
Or maybe a theory of quantum gravity (an extension to GR)
would not predict a singularity.
As I said in post #11, which is not all that far back. And
as I implied in the last sentence of post #16, less than
twelve hours ago.

The prediction of the singularity of the beginning of the
Universe was so profound that it gave the title to what
may be the most well-known popular science book ever
written: "A Brief History of Time" It is the notion that
time started at the Big Bang which GR predicts and labels
a "singularity".



And wouldn't it be more accurate to say that density is
undefined, as it involves a division by zero?
No, the density clearly and unambiguously approaches
infinite value asymptotically as the time is asymptotically
regressed to t=0. I see no reason to avoid saying so.

-- Jeff, in Minneapolis

Jeff Root
2014-Jul-21, 07:26 PM
Does "infinite density" make sense to you? :confused:
Rather surprisingly, yes, it does.

My own guess is that the density was never *extremely*
high in the first moments of the Big Bang, but that, as I
suggested a couple of posts back, the mass-energy of the
Universe grew from zero to a very large value over some
(possibly very, very short) period of time. But still, I have
no problem with idea of the matter in the center of a black
hole becoming more and more dense without limit as it is
continually crushed more and more by its own weight.
It would only reach infinite density in infinite time, which
does seem like a sort of cop-out... especially considering
how quickly it would reach densities QM can't describe.

-- Jeff, in Minneapolis

Strange
2014-Jul-21, 07:36 PM
My own guess is that the density was never *extremely*
high in the first moments of the Big Bang, but that, as I
suggested a couple of posts back, the mass-energy of the
Universe grew from zero to a very large value over some
(possibly very, very short) period of time.

Maybe you would like to support that in ATM?

mkline55
2014-Jul-21, 07:38 PM
Does "infinite density" make sense to you? :confused:

It is the prediction of infinite density, among other things, that demonstrates GR has gone off the tracks.
"Other things" meaning what? Time? Distance? Expansion velocity? Something else?

Cougar
2014-Jul-26, 12:35 PM
"Other things" meaning what? Time? Distance? Expansion velocity? Something else?

Well, I mainly added that so as not to be overly limiting in my statement. But the "singular" conclusion typically claims infinite density along with zero volume - another prediction that makes utterly no sense at all. I think it was caveman who pointed out that it is not "the mathematics" of GR that "break down." The mathematics work just fine. But, I would add, the conclusion or prediction that the mathematics leads to involves impossible, nonsensical infinities. When this happens in physics, it basically means "back to the drawing board."

effingham
2014-Jul-26, 06:05 PM
We know that the "big bang" in the sense of the universe expanding from an earlier hot, dense state happened - and is still happening. That is what the term origianlly described.

Since then the popular press and some science writers have used it to refer to some sort of "creation event"; it is probably true that we don't know if such a thing happened or not.
Until such evidence arises showing that the universe

a) is expanding (Expanding into what, exactly? Do you even realize the logical absurdity of "expanding universe"? The universe is all that exists, into what can it expand if it encompasses all that exists? Ex nihilo creation myth, anyone? Expanding universe is "fact" yet expanding earth is met with hysterical crying?)

and/or b) the universe has an origin, edge, limit, side, top, bottom, inside, outside and/or an end, both these notions may safely be deemed riotous fantasy.

Consensus of belief systems is not a requisite of science. It doesn't matter how many people believe in a creation myth, it is still a myth until some evidence arises supporting it.

effingham
2014-Jul-26, 06:07 PM
Relatively minor disagreements with Shaula and Wayne:

General relativity plus the observation that galaxies are
moving apart unambiguously predicts a singularity. That
singularity was the beginning of the Universe. GR has no
problem with that, all the way back to t=0.

It so happens that close to the singularity, the energy
density approaches infinite. At t=0 it would have been
infinite. Neither of those fits in with the known laws of
quantum mechanics. So either there was no singularity,
or the laws of QM need to be added to, or GM needs to
be revised, or some combination of the above.

I think it is clear that QM has to be extended in order to
account for the Big Bang. That could result in elimination
of the singularity without any change to GR. Or it could
simply alter the conditions near the singularity such that
the density did not approach infinite.

-- Jeff, in Minneapolis
Not all galaxies are moving apart, your gibberish thesis is invalid therefore.

effingham
2014-Jul-26, 06:08 PM
The big bang was more a point in time than space. It could have been any size, including infinite. It is problematic to dimensionalize the big bang. We know, for example, the surface of last scattering appeared about 400,000 years after the BB, but, cannot assign it a size - only a scale factor relative to 'today'. We would need to know the entire expansion history of the universe, which is unknown, to even make an approximation.
"surface of last scattering" is a spurious notion with utterly no empirical referent

effingham
2014-Jul-26, 06:09 PM
Bah didn't notice this was an old post...that I already replied to.

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

We don't. In fact saying the big bang started from a size of zero volume is not really science. It is a pop sci answer that extrapolate further back then the models allow. The observable universe started out very small and we can calculate that back with high energy physics to smaller then a proton but there is a point before that were our models break down.

The big bang assumes as non zero volume of space to begin with. Until we get a proper quantum theory of gravity we probably won't be able to say much on what happened before the point where our current models fail.
Now the why was the observable universe smaller then a proton and not the size of the moon? I believe the answer to that lies more in that there is no reason it should stop at the size of the moon. Our current theories work many orders of magnitude beyond that size. The trick seemed to be how did the early universe get big enough that it didn't immediately crunch back down on itself and that seem to because the initial inflation was fast enough to get over that limit.
Compressing matter until it is smaller than a proton defies all known physical laws, it is sheer fantasy.

effingham
2014-Jul-26, 06:13 PM
We do know that it happened. We have multiple lines of evidence that it happened. If it didn't happen we wouldn't be here :P
Seriously the Big Bang is the best explanation for the observations we have and we have a ton of observations that all point to the same thing. That our observable universe was in a very hot dense state and that it had a rapid period of inflation...blah blah blah...current day cosmic expansion is not only happening but also increasing in its rate.
I understand you have faith in your belief system, but science requires experimental verification. No verification exists for the Incredible Shrinking Universe belief system. We're not privy to all the previous states of the universe, the only thing we can say with certainty is that the universe obeys physical laws, whereas "big bang" myths violate virtually all known physical laws, for example the known incompatibility of solid and liquid matter, the "Isles of stability" principle of nuclear physics, ex nihilo creation and the list goes on and on.

effingham
2014-Jul-26, 06:16 PM
No, as I've said maybe six or seven times in various different
threads, including previously in this one, I meant QM, not GR.

And as I've said several times, we know for sure that QM has
to be extended to account for whatever happened at the Big
Bang. As it stands now, it can't do that. Extending it in that
way might, for example, describe how all the matter-energy
of the Universe came into existence over a period of time
(maybe a second, or a picosecond), eliminating the infinite
density predicted by GR. No change needs to be made to GR
to change the result of GR's prediction. GR's prediction is
calculated with the assumption that the mass-energy of the
Universe doesn't change.

If I have an apple (which I do), and multiply the number of
apples I have by two every day, in less than two months I'll
have over a quintillion apples. Certainly that number of
apples doesn't exist in the whole world. Multiplication must
be incorrect, mustn't it? It failed by predicting an impossible
number of apples in a perfectly reasonable period of time.

Or maybe one of the inputs into the multiplication was wrong.
Maybe it wasn't a failure of multiplication, but a failure to
account for the fact that I can't increase the number of apples
I have in the way I assumed.

GR might be incomplete, like QM, but the fact that it predicts
a singularity and infinite density at t=0 is not a failure of GR.
It is a correct prediction by GR from the assumption that the
mass-energy of the Universe is unchanging.

-- Jeff, in Minneapolis
Your apt description of the disconnect between math and reality underscores the absolute requirement of experimental verification in science. Math is not science and is a good substitute for creative fiction, a **** poor substitute for scientific rigor.

effingham
2014-Jul-26, 06:18 PM
No, as I've said maybe six or seven times in various different
threads, including previously in this one, I meant QM, not GR.

And as I've said several times, we know for sure that QM has
to be extended to account for whatever happened at the Big
Bang. As it stands now, it can't do that. Extending it in that
way might, for example, describe how all the matter-energy
of the Universe came into existence over a period of time
(maybe a second, or a picosecond), eliminating the infinite
density predicted by GR. No change needs to be made to GR
to change the result of GR's prediction. GR's prediction is
calculated with the assumption that the mass-energy of the
Universe doesn't change.

If I have an apple (which I do), and multiply the number of
apples I have by two every day, in less than two months I'll
have over a quintillion apples. Certainly that number of
apples doesn't exist in the whole world. Multiplication must
be incorrect, mustn't it? It failed by predicting an impossible
number of apples in a perfectly reasonable period of time.

Or maybe one of the inputs into the multiplication was wrong.
Maybe it wasn't a failure of multiplication, but a failure to
account for the fact that I can't increase the number of apples
I have in the way I assumed.

GR might be incomplete, like QM, but the fact that it predicts
a singularity and infinite density at t=0 is not a failure of GR.
It is a correct prediction by GR from the assumption that the
mass-energy of the Universe is unchanging.

-- Jeff, in Minneapolis
t = 0 is not a failure of math, you're right, it's a failure of the notion of counting time backwards to 0. We don't see any evidence the universe (or time) ever had an origin, so speculations about such an origin are straying off into hallucinatory terrain.

Strange
2014-Jul-26, 06:20 PM
Until such evidence arises showing that the universe

There are multiple lines of evidence.


a) is expanding (Expanding into what, exactly?

It is not expanding "into" anything. The distance between things is increasing.


Ex nihilo creation myth, anyone?

No.


Expanding universe is "fact" yet expanding earth is met with hysterical crying?)

The expanding universe is not a fact, it is a theory. In other words, it is supported by evidence.


Consensus of belief systems is not a requisite of science.

Did anyone say it was?

Strange
2014-Jul-26, 06:24 PM
I understand you have faith in your belief system, but science requires experimental verification.

If by that you mean, for example, the theory making a prediction that is later confirmed by observation then that is exactly why the big bang model is currently the accepted theory.


whereas "big bang" myths violate virtually all known physical laws, for example the known incompatibility of solid and liquid matter, the "Isles of stability" principle of nuclear physics, ex nihilo creation and the list goes on and on.

I don't know what most of the things on that list refer to but as "ex nihilo creation" is a strawman (i.e. not part of the big bang model) then I guess they are equally irrelevant.

effingham
2014-Jul-26, 06:24 PM
There are multiple lines of evidence.



It is not expanding "into" anything. The distance between things is increasing.



No.



The expanding universe is not a fact, it is a theory. In other words, it is supported by evidence.



Did anyone say it was?
Your belief system not only proposes the ridiculous notion that the universe is "expanding" but also that there is space outside (i.e. more universe) it into which it can expand. If you do not see the absurdity of this idea, I doubt anyone can help you see it.

Strange
2014-Jul-26, 06:25 PM
Your belief system not only purposes the ridiculous notion that the universe is "expanding" but also that there is space outside

There is nothing "outside".

effingham
2014-Jul-26, 06:33 PM
There is nothing "outside".
There is not even an "outside" into which this nothing you reference can (not) exist.

Shaula
2014-Jul-26, 07:25 PM
Your belief system not only proposes the ridiculous notion that the universe is "expanding" but also that there is space outside (i.e. more universe) it into which it can expand. If you do not see the absurdity of this idea, I doubt anyone can help you see it.
Totally and utterly wrong. The theory has no need for space outside the universe to expand into. Suggest you read up on metric expansion or start your own thread asking about this because you are very, very far from the mark here.

effingham
2014-Jul-26, 07:26 PM
totally and utterly wrong. The theory has no need for space outside the universe to expand into. Suggest you read up on metric expansion or start your own thread asking about this because you are very, very far from the mark here.
esad

Strange
2014-Jul-26, 07:30 PM
esad

I assume that is short for "that's what he said" (in reference to my earlier post) :)

effingham
2014-Jul-26, 07:33 PM
I assume that is short for "that's what he said" (in reference to my earlier post) :)
No, it's short for [censored]

Strange
2014-Jul-26, 07:42 PM
No.

I assume you are trying to get banned so that you can claim that your "scientific" ideas were censored.

WayneFrancis
2014-Jul-28, 04:49 AM
Until such evidence arises showing that the universe

a) is expanding (Expanding into what, exactly? Do you even realize the logical absurdity of "expanding universe"? The universe is all that exists, into what can it expand if it encompasses all that exists? Ex nihilo creation myth, anyone? Expanding universe is "fact" yet expanding earth is met with hysterical crying?)

and/or b) the universe has an origin, edge, limit, side, top, bottom, inside, outside and/or an end, both these notions may safely be deemed riotous fantasy.

Consensus of belief systems is not a requisite of science. It doesn't matter how many people believe in a creation myth, it is still a myth until some evidence arises supporting it.

Forgetting the rest of the tirade of straw men you put up in all these posts I'll focus on the "expanding into what" portion. This clearly shows that you have absolutely no understanding of General Relativity beyond those 2 words and maybe that Einstein discovered the theory. GR predicts that the manifold of a universe would not be static. That it should, in fact, change. In this case it is expanding. It doesn't say and doesn't need to expand into anything. Saying it does is an indication that you think the big bang is some type of explosion in a preexisting space. Before anyone calls anything that the majority of experts in the relative field, no pun intended, agree upon perhaps you should actually learn what the theory actually says and not rely on the inaccurate representation of the theory you have in your head.

Jens
2014-Jul-28, 11:35 PM
Does "infinite density" make sense to you? :confused:

It is the prediction of infinite density, among other things, that demonstrates GR has gone off the tracks.

This seemed like quite an interesting discussion but seems to have derailed a bit. But in reference to this issue, there is something I've considered and though it's not mainstream, would offer it as speculation. Now if the universe is made of an infinite hierarchy of particles, like those Russian dolls (something for which there is no physical evidence) then you never get to the infinity because there is always something deeper to collapse. It also explains away the fact that the gravitational force of a point particle becomes infinite at the point. Do others find this absurd, or merely speculative?

WayneFrancis
2014-Jul-29, 04:04 AM
This seemed like quite an interesting discussion but seems to have derailed a bit. But in reference to this issue, there is something I've considered and though it's not mainstream, would offer it as speculation. Now if the universe is made of an infinite hierarchy of particles, like those Russian dolls (something for which there is no physical evidence) then you never get to the infinity because there is always something deeper to collapse. It also explains away the fact that the gravitational force of a point particle becomes infinite at the point. Do others find this absurd, or merely speculative?

What happens when you get stuff that has to be smaller then the planck length?

Jens
2014-Jul-29, 04:16 AM
What happens when you get stuff that has to be smaller then the planck length?

My impression is that the Planck length is a length beyond which you cannot measure length. I don't think the physical significance is known, but it does mean that it would perhaps in principle be impossible to prove or disprove the existence of smaller sub-particles.

Ken G
2014-Aug-02, 07:20 AM
But still, I have
no problem with idea of the matter in the center of a black
hole becoming more and more dense without limit as it is
continually crushed more and more by its own weight.
It would only reach infinite density in infinite time, which
does seem like a sort of cop-out...
Part of the problem is that it would not require an infinite time, GR predicts the density would pass any given limit in a finite, and indeed rather short, amount of time. But it's clear that our simplistic notions like "volume" and "density" aren't going to work then anyway, so "infinite density" has essentially no meaning. Einstein himself worked on theories that would have different physics than GR, and there is zero reason to think that GR would be right in those limits, since that's not how physics works.