# Birth Home of our Universe?

1. Jan 22, 2004

### pallidin

Greetings,

Not sure if this has been asked before. Feel free to refer to any previous post.

My question is this: Since we know that our universe is expanding, has an extrapolation been done to approximate the actual origin in space of the Big Bang?

2. Jan 22, 2004

### Jimmy

I think since space itself is expanding, the origin of the big with respect to space is meaningless. The big bang happened everywhere, although that everywhere at the time of the BB was pretty small.

If I'm correct, not exactly sure, the farthest we can look back (directly) is approximately 500,000 years after the BB, during the time of photon decoupling. This happened when the universe was cool enough to become transparent to electromagnetic radiation. This is the source of the microwave background radiation. Today, you can look in any direction and see this radiation. In essence, the origin of the universe surrounds us.

http://hyperphysics.phy-astr.gsu.edu/hbase/bkg3k.html

Edit: When I said meaningless, I wasn't critisizing your question. Just that there is no origin of the universe with reference to space. Where the BB happened in relation to what may lie outside what we call the universe would be an interesting discussion. Are there other 'big bangs' and 'big crunches' happening, etc.

Last edited: Jan 22, 2004
3. Jan 22, 2004

### pallidin

Small? Is no "locality" suggested? Surely it MUST be within our current frame of referance... somewhere.??

4. Jan 22, 2004

### Jimmy

I suppose small might be a meaningless word as well in reference to the big bang. I'm not really sure. I'm also not aware of any frame in which you can reference the origin of the BB. That doesn't mean a frame doesn't exist. I just don't think anyone really knows. As far as space goes, you definitely can't pick one point and say that the origin of the BB was there...

5. Jan 22, 2004

### pallidin

Indeed!

6. Jan 22, 2004

### pallidin

Do we not, in fact, exist in that very frame?

7. Jan 22, 2004

### Nereid

Staff Emeritus
Where did the BB originate, in terms of today's locations? Well, it was inside my PC, in your big left toe, at Jimmy's mother's old home, on marcus' primary school desk, at the centre of the Sun, in a dust mote in the outer reaches of 3C273, ... in other words, everywhere in the universe today is exactly where the universe started expanding from.

According to the WMAP results, the earliest we can see (so far) is the 'surface of last scattering', which according to the best fitting models was 379,000 years after t = 0.
http://map.gsfc.nasa.gov/m_mm.html

If we ever succeed in detecting relict neutrinos, we will be able to see an earlier surface of last scattering (sorry to say I don't have an estimate to hand of how soon after the BB that would likely be).

Of course, the great 'let out' clause is that we can't know anything about the first ~10-43 seconds (Planck time), because we know that our best physics (GR and QFT) cannot both work in this period. If we convince ourselves that String Theory/M Theory/LQG/Monty Python is how the universe 'really' is, then we may be able to say for sure that it all began in your living room.

8. Jan 22, 2004

### Cecil

Here's a good analogy. Consider a loaf of raisin bread, with soem evenly spaced raisins. When you put it in the oven, it expands and all the raisins move away from each other. There is no "center" of expansion.

Now, if you imagine that before being baked the dough and raisins were all concentrated into a single point, you see that the Big Bang really did happen EVERYWHERE in the universe, since all matter that exists was originally concentrated in one point.

9. Jan 22, 2004

### Jimmy

10. Jan 22, 2004

### Jimmy

11. Jan 22, 2004

### Nereid

Staff Emeritus
Ain't she the centre of the universe?

12. Jan 22, 2004

### pallidin

May I suggest that if the universe "started expanding" that it must have a local origin? An origin of expansion. If there is no origin of expansion, expansion itself is not possible ????

13. Jan 22, 2004

### Jimmy

Of course. But she isn't in an 'old home'. lol!

Last edited: Jan 22, 2004
14. Jan 22, 2004

### Jimmy

There isn't a center of expansion. Any location in the universe appears to be at the center of expansion. From any point, the farther you look out into space, the faster space will appear to be expanding. That's why more distant galaxies are receding faster than galaxies that are closer.

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

15. Jan 22, 2004

### Nereid

Staff Emeritus
oops, please excuse my poor choice of words; I meant 'the home she lived in when she was a little girl' {insert Smilie of Nereid with a red face}

16. Jan 22, 2004

### Jimmy

Haha! Don't sweat it. I was never offended. I thought you were just kidding around anyway. I understand now though. It's my mistake really. I just jumped to the wrong conclusion. An 'old home' isn't necessarily a on 'old folks home'.

Thanks, Nereid.

Last edited: Jan 23, 2004
17. Jan 22, 2004

### pallidin

OK. Please offer corrections on the following assumptions:

1) Expansion is a function. It is a function of separation. Without separation, the function of expansion is impossible.

2) Separation directly implies and demands origin.

3) Complex expansion functions are characterized by a net internal "pseudo origin"

4) Regardless of whether or not the expansion function is simple or complex, the potential of expansion must be initially constrained/contained to some degree, else expansion is not possible, as there would be no relative frame to ascribe the event of expansion.

18. Jan 22, 2004

### pallidin

So, basically are we saying this:

If I am on earth, viewing Alpha Centauri, then Alpha Centauri is receeding. And if I am on Alpha Centauri viewing earth, then the earth is receeding.

Hello!! What's wrong with this picture? If everything is expanding relative to one another, then it follows that everything at a previous time was in the same place.

19. Jan 22, 2004

### Jimmy

Yes. That's how Edwin Hubble's findings were interpreted which evolved into the Big Bang theory. The universe itself is expanding; space-time included. The question is, where was the universe when the expansion started? is it in the same place now as it was then?

20. Jan 23, 2004

### Phobos

Staff Emeritus
The origin is at Time = 0. (Space and Time are intimately linked...which is why we speak of "spacetime".) This is a point that is inaccessable to us (since time is a one-way street) except through ancient images that approach that origin as captured by our telescopes. Space alone has no such origin. It is the entirety of existence that matter and energy reside in. The expansion is what we see as the behavior of space to drive galaxies apart as time marches on. Or am I mixing up cause and effect and it's the expansion of space that drives time forward? Guess I'm back to the linking of spacetime - the very fabric of the universe.

21. Jan 23, 2004

### Jimmy

I've often wondered how entropy and time (or our perception of time) are related. As the universe expands it cools and entropy increases. This seems to be a one way street just as time seems to be moving (or how we move through time) in one direction(forward).

If the microwave background radiation reflects the temperature of the universe and if it is a function of time, can that be used as an absolute measure of the march of time? Do space-time curvatures and varying velocities simply introduce distortions in measurements of an absolute time at local scales?

I'm always afraid to use the word 'absolute' but I can't help but wonder.

22. Jan 23, 2004

### hellfire

Yes, I wonder this also. I started learning QM (Sakurai) and GR (Schutz) by myself and from the perspective of my mediocre understanding, I see the following problem.

Assuming thermal equilibrium, entropy is related to the number N of energetic states of a system as $$S = - k \sum_{i} w_i ln w_i$$, with w_i standing for the diagonal elements of the density matrix. To find out something about the relation between time and entropy we should, therefore, define first the energy states for the gravitational field (space-time), to be able afterwards to define the entropy of gravitational systems. But is there an unambiguous definition of the energy of space-time? I wonder also that in GR gravity is not affected by the energetic content of space-time energy, at least not in the same way as by the energy density of matter, described by the stress-energy tensor.

I hope this is not considered as too off-topic here.

Regards.

23. Jan 23, 2004

### pallidin

Not at all. All those responding have indicated that my questions may simply have no definitive answers at this point, until more is known about our universe.
Given that, your "tangent" and is most welcome, as it is related. I hope that you and Jim continue the discourse, either here or throughout PF, as I find you both to be very informative and progressive.

24. Jan 23, 2004

### Jimmy

Gee, no one has ever called me progressive before. Thanks Pallidin!

In reality, I know very little compared to many of the users here. As far as hellfire's last post, I'm afraid what he's saying is beyond my grasp at this point in time.

Getting back to your original question, Pallidin, I thought Phobos' origin for the BB of time=0 was a good point. I'd wish I would have had the presence of mind to think of that.