The Big Bang And Question(s)

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I'm pretty ignorant in physics, so please help me out.

OK... So I was watching the special "How The Universe Works", and the episode was about the origins of the universe. (Lame, I know, but Netflix had nothing else that was interesting). They keep talking about the speed at which the Big Bang created the universe, which was something like a millionth of a millionth of a millionth of a millionth of a second to expand from the size of a golf ball to the size of the Earth. They go on to describe Planck time and more exact figure and stuff, but my question is more general.

The question is this: How are we even able to measure any form of time, when (at least as it has been explained to me), time was created with the Big Bang? I mean... they talk about expansion into not even space, just emptiness or whatever existed before the Big Bang... so how can we even give that a referenced scale? Is our initial point of reference just referring to the first observable time unit within the universe and its expansion from that? Because to me it seems like everyone talks about it as though the 'emptiness' that existed before the Big Bang can still be measured in time.

This also goes along with the question about how the Big Bang expanded faster than the speed of light.

If anyone could shed light on this (please avoid the obvious pun) then I would be grateful. If my question is being asked incorrectly, please logically explain to me what is wrong with it so I can understand.

Thanks!
 

Answers and Replies

  • #2
Chronos
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Matter does not 'move' during inflation. The speed limit c only applies to matter with respect to inertial reference frames. It does not apply to the space between particles of matter.
 
  • #3
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OK. I understand that. But what does it mean to say that the Big Bang expanded at such and such a speed/time when that speed/time doesn't exist outside it's own creation?
 
  • #4
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BBT cosmology uses human scale or matter as the reference frame.
So space is expanding relative to us.

Personally, I think that choice of reference frame may be flawed, and a slight bending of the cosmological principle.
 
  • #5
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OK. I understand that. But what does it mean to say that the Big Bang expanded at such and such a speed/time when that speed/time doesn't exist outside it's own creation?
It means that in few tiny fractions of a second it expanded exponentially. Once dimensionality was manifested, you can measure it. You can assign time coordinate to beginning of inflation, and you can do it for end of inflation, thus you know its duration.

BBT cosmology uses human scale or matter as the reference frame.
So space is expanding relative to us.

Personally, I think that choice of reference frame may be flawed, and a slight bending of the cosmological principle.
I don't understand what are you trying to say.
 
  • #6
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It means that in few tiny fractions of a second it expanded exponentially. Once dimensionality was manifested, you can measure it. You can assign time coordinate to beginning of inflation, and you can do it for end of inflation, thus you know its duration.

I don't understand what are you trying to say.
The concept of expansion implies a reference frame for a coordinate system in which space is expanding against some unit of measurement.
BBT choose to measure the universe against the locally experienced human reference frame.
The metric expansion of space offers an infinit number of possible alternative reference frames all expanding or accelerating relative to each other.
The basic laws of physics and motion can only be correct in one of the over long periods of time.
You can get some very interesting alternative cosmolgies from alternative reference frames.
 
  • #7
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The concept of expansion implies a reference frame for a coordinate system in which space is expanding against some unit of measurement.
BBT choose to measure the universe against the locally experienced human reference frame.
The metric expansion of space offers an infinit number of possible alternative reference frames all expanding or accelerating relative to each other.
The basic laws of physics and motion can only be correct in one of the over long periods of time.
You can get some very interesting alternative cosmolgies from alternative reference frames.
No, concept of expansion implies comoving frame of reference. Nothing to do with locally experienced human reference frame. Comoving observers are the only ones that expirence universe as isotropic, which is a requirment for using FLRW metric, which in turn enables you to derive scale factor as a function of cosmological time.

Edit: I should have said "concept of isotropic expansion", because there is really no reference frame in which universe is not expanding. Question is if expansion is perceived as isotropic, or not. That makes case of comoving coordinates as most natural ones even stronger.
 
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  • #8
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No, concept of expansion implies comoving frame of reference. Nothing to do with locally experienced human reference frame. Comoving observers are the only ones that expirence universe as isotropic, which is a requirment for using FLRW metric, which in turn enables you to derive scale factor as a function of cosmological time.

Edit: I should have said "concept of isotropic expansion", because there is really no reference frame in which universe is not expanding. Question is if expansion is perceived as isotropic, or not. That makes case of comoving coordinates as most natural ones even stronger.
Indeed one of my favourite alternative cosmologies "Condensing universe" has something very close the comoving distance as the absolute distance. ie space not expanding.
It does look a bit nasty because it assume a reference frame for physics where matter is shrinking at a bit more than 6% a billion years. (an atom on your metre ruler every 6 years or so) Also time dilation is an indirect property of shrinking matter.

Anyway bringing the thread back on track ....:smile:
 
  • #9
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Indeed one of my favourite alternative cosmologies "Condensing universe" has something very close the comoving distance as the absolute distance. ie space not expanding.
It does look a bit nasty because it assume a reference frame for physics where matter is shrinking at a bit more than 6% a billion years. (an atom on your metre ruler every 6 years or so) Also time dilation is an indirect property of shrinking matter.

Anyway bringing the thread back on track ....:smile:
Then you should ask yourself why is that your favorite cosmology. It utterly complicates things without one single gain in understanding. We need to have starting point. There is no questioning that distances between galaxies are increasing relative to the size of atoms. Can we describe same physics by saying that space is not expanding on large scales, but instead atoms are shrinking and space is contracting on small scales? Probably yes, but we are introducing two variables instead of one, which is bad. So, what's the point?
 
  • #10
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Then you should ask yourself why is that your favorite cosmology. It utterly complicates things without one single gain in understanding. We need to have starting point. There is no questioning that distances between galaxies are increasing relative to the size of atoms. Can we describe same physics by saying that space is not expanding on large scales, but instead atoms are shrinking and space is contracting on small scales? Probably yes, but we are introducing two variables instead of one, which is bad. So, what's the point?
Mostly just as a fun hobby.
But this case is very interesting, most alternate cosmologies you can kill off almost instantly they just don't match observation. I have looked at loads of them.
This one is very hard to break.
It gives a very different view of a universe that matches raw observations, but not their interpretation.
If space is not expanding then there was no big bang, etc.

If conservation of momentium works in that reference frame, then in the BBT reference frame matter speeds up relative to local space as space expands.
This sounds very odd till you combine it with gravity, it make gravity look stronger or masses bigger over large time scales.
If I still can't break it, I will post a thread on it. It is on other forums, but I have not updated any of them for a while.
 
  • #11
Chalnoth
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Mostly just as a fun hobby.
But this case is very interesting, most alternate cosmologies you can kill off almost instantly they just don't match observation. I have looked at loads of them.
This one is very hard to break.
It gives a very different view of a universe that matches raw observations, but not their interpretation.
If space is not expanding then there was no big bang, etc.

If conservation of momentium works in that reference frame, then in the BBT reference frame matter speeds up relative to local space as space expands.
This sounds very odd till you combine it with gravity, it make gravity look stronger or masses bigger over large time scales.
If I still can't break it, I will post a thread on it. It is on other forums, but I have not updated any of them for a while.
Nah, the "condensing universe" is just a change in coordinates. You can't change the physics with just a change in coordinates. The big bang singularity is physical (within the theory), meaning it is there no matter which coordinates you use. It looks different, in that at that singularity matter is infinitely-large, instead of space being infinitely-small. But the singularity is still there.

Of course, the prediction of a physical singularity is the main reason why the big bang theory cannot be trusted that far back. And you can't get rid of it without replacing General Relativity with a quantum theory of gravity.
 
  • #12
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OK. Assigning a time coordinate makes sense I guess. I'll just have to think about the whole thing a little longer.

The conversation you guys are having is helping though! Keep going :)
 
  • #13
cmb
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The speed limit c only applies to matter with respect to inertial reference frames. It does not apply to the space between particles of matter.
Really!? Have I misunderstood your point?

So if we were to look at an equation for the curvature of space-time around a mass, we'd not find a 'c' term in it?
 
  • #14
Chalnoth
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Really!? Have I misunderstood your point?

So if we were to look at an equation for the curvature of space-time around a mass, we'd not find a 'c' term in it?
"c" is a unit conversion factor, so you see it in all sorts of places depending upon what units you use.
 
  • #15
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Nah, the "condensing universe" is just a change in coordinates. You can't change the physics with just a change in coordinates. The big bang singularity is physical (within the theory), meaning it is there no matter which coordinates you use. It looks different, in that at that singularity matter is infinitely-large, instead of space being infinitely-small. But the singularity is still there.

Of course, the prediction of a physical singularity is the main reason why the big bang theory cannot be trusted that far back. And you can't get rid of it without replacing General Relativity with a quantum theory of gravity.
It does not change physics, but the two reference frames or coordinate systems are accelerating/expanding relative to each other.
An object moving at constant velocity in one is accelerating in the other ref frame.
If you assume the TCU reference frame is the correct one for the laws of physics then the correction factors for BBT look similar to dark matter and dark energy, at the very large scale.

In the TCU version of things the universe also starts infinitely slowly as well as large (thousands of billions of years to get going)

The maths for the conversion back BBT, does make space expand faster than the speed of light, but objects can never exceed the speed of light relative to there local reference frame.:wink:
 
  • #16
Chalnoth
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It does not change physics, but the two reference frames or coordinate systems are accelerating/expanding relative to each other.
An object moving at constant velocity in one is accelerating in the other ref frame.
If you assume the TCU reference frame is the correct one for the laws of physics then the correction factors for BBT look similar to dark matter and dark energy, at the very large scale.

In the TCU version of things the universe also starts infinitely slowly as well as large (thousands of billions of years to get going)

The maths for the conversion back BBT, does make space expand faster than the speed of light, but objects can never exceed the speed of light relative to there local reference frame.:wink:
I have no idea what you're trying to say here. There is no physical difference between the two.
 
  • #17
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I have no idea what you're trying to say here. There is no physical difference between the two.
In the BBT ref frame galaxies move further apart as space expands.
In the TCU ref frame galaxies stay the same distance apart but slowly shrink.

If you put a fixed size box around the nearest 1000 galaxies (size fixed in coord system of that ref frame)
In BBT the galaxies expand out of the box, but in TCU they all just stay still only perturbed by gravity.
Viewed rom the TCU ref frame the BBT box shrinks leaving the galixies behind.

In TCU an object traveling between two galaxies arrives in the same way as a person just crossing the street at constant velocity.
But in BBT the two galaxies get further apart as the object travels increasing travel time.

Viewed from TCU and object traveling at constant velocity in BBT is slowing as that reference frame shrinks.

Conservation of momentum cannot work in both reference frames. One has to be wrong.
 
  • #18
Chalnoth
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In the BBT ref frame galaxies move further apart as space expands.
In the TCU ref frame galaxies stay the same distance apart but slowly shrink.

If you put a fixed size box around the nearest 1000 galaxies (size fixed in coord system of that ref frame)
In BBT the galaxies expand out of the box, but in TCU they all just stay still only perturbed by gravity.
Viewed rom the TCU ref frame the BBT box shrinks leaving the galixies behind.

In TCU an object traveling between two galaxies arrives in the same way as a person just crossing the street at constant velocity.
But in BBT the two galaxies get further apart as the object travels increasing travel time.

Viewed from TCU and object traveling at constant velocity in BBT is slowing as that reference frame shrinks.

Conservation of momentum cannot work in both reference frames. One has to be wrong.
Well, momentum isn't conserved in an expanding universe anyway.

However, in any space-time, you can always transform to a local coordinate system where momentum is conserved.
 
  • #19
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Well, momentum isn't conserved in an expanding universe anyway.

However, in any space-time, you can always transform to a local coordinate system where momentum is conserved.
Anyway, that reference frame does provide an interesting alternative cosmology, in which it is a bit easier to explain some observations that get very messy in BBT.
 
  • #20
Chalnoth
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Anyway, that reference frame does provide an interesting alternative cosmology, in which it is a bit easier to explain some observations that get very messy in BBT.
Again, it's not an alternative. And it's generally expected that some things are easier to understand in certain coordinate systems rather than others.
 
  • #21
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Again, it's not an alternative. And it's generally expected that some things are easier to understand in certain coordinate systems rather than others.
It is not just a change of coordinate systems!

Just viewing the the universe from the Condensing Universe ref frame would be purely a coord system change.

But by assuming the laws of physics work correctly in the TCU frame, and are therefore are broken in the BBT ref frame.
You are changing the basic laws of motion as viewed from both viewpoints.
 
  • #22
Chalnoth
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It is not just a change of coordinate systems!

Just viewing the the universe from the Condensing Universe ref frame would be purely a coord system change.

But by assuming the laws of physics work correctly in the TCU frame, and are therefore are broken in the BBT ref frame.
You are changing the basic laws of motion as viewed from both viewpoints.
With one significant caveat, the laws of physics work correctly in all reference frames.

That caveat is that we don't know how to reconcile quantum mechanics with General Relativity, which in turn means that we don't know how to properly do quantum mechanics in curved space-time. But any space-time can be represented as locally-flat, so we can do quantum mechanics locally, provided the interactions happen in sufficiently-small space-time curvature that the locally-flat approximation holds.

This means that whenever you want to do something with quantum mechanics, the right reference frame is one that is locally-flat.

But with that caveat aside, all laws of physics are independent of reference frame.
 
  • #23
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With one significant caveat, the laws of physics work correctly in all reference frames.

That caveat is that we don't know how to reconcile quantum mechanics with General Relativity, which in turn means that we don't know how to properly do quantum mechanics in curved space-time. But any space-time can be represented as locally-flat, so we can do quantum mechanics locally, provided the interactions happen in sufficiently-small space-time curvature that the locally-flat approximation holds.

This means that whenever you want to do something with quantum mechanics, the right reference frame is one that is locally-flat.

But with that caveat aside, all laws of physics are independent of reference frame.
Sorry yes, I should say," appears broken as viewed from the reference frame" not "is broken".

If you assume the universe is expanding and the viewpoint is not effected then no viewpoint correction is expected to be needed, but this is not so for a viewpoint that is shrinking.

I just think it is interesting that the effect caused when combined with gravity looks very much like what is expected from dark matter and dark energy.
 
  • #24
Chalnoth
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I just think it is interesting that the effect caused when combined with gravity looks very much like what is expected from dark matter and dark energy.
You can't get away from the need for dark matter or dark energy by changing coordinate systems.
 
  • #25
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You can't get away from the need for dark matter or dark energy by changing coordinate systems.
Remember is do not own a super computer, and this is only my hobby modeling this stuff.

So, if space is not expanding, that kills of dark energy straight away.

With space not expanding, gas must still be falling out of the voids into the large scale structures, and formation of the large scale structures must be accelerating as they gain mass.
Backtracking worst case data I could find (dark flow, corresponding to mega structures) then I get a very rough age of 700 to 1300 billion years.
Long before first neutrons at z = 1014 430 to 480 billion years ago.
(not sure if this is a problem or not)(assuming conservation of momentum and gravity work as expected in TCU coords)

That gas must then fall into the galactic clusters at a high rate.
There is nothing to stop it falling into galaxies at the same high rate.
If the mass of galaxies was much higher than the visible mass, the impact speed would cause the surface of galaxies to glow. (This puts a low upper limit of dark matter in galaxies)

If galaxies are growing as they gain mass they cannot be gravitationaly bound, otherwise they would just colapse smaller under increasing gravity.

Modeling spiral galaxies with only the central buldge gravitaionaly bound and growing at a near exponential rate of 30% every billion years you get a get a good match to raw redshift curves.
This assumes the gas spirals in and large amounts of dense matter gets ejected out.
The problem becomes keeping the mass of galaxies low not hight.

This implies that the sun and observalble local stars should have a radial component to thier velocity away from the centre of the galaxy of about 37 to 45 km/s.
This is not observed but some mention of gravitation redshift is mentioned, that would not apply to a very low mass galaxy.
 

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