Expanding Universe

[Time_Travel]

I don't understand the concept of the Expanding Universe(EU).

I read all the theory about the EU but could n't understand the expanding Concept.

Does it mean that a billion years ago every thing (Galaxies)was much closer to each other than it is now????

 

I still have a lot more questions regarding this EU. Could you guys clearly explain this .

[sanctus]

I guess you read too advanced theory, because then it is hard to understand ;-)

 

Anyway, yes, that is the way it seems to be. It is more more fun, the universe seem s to be in accelerated expansion, which means the further you go away the quicker things (galaxies, galaxy-clusters,...) receede from us. But no wrong conclusions from here, this does not imply that we are at the center of the universe.

 

The expanding universe has also other consequences, it is the reason why we see the cosmic microwave background radiation (CMB or sometimes CMBR). Just after the bigbang the universe was so dense that the photons in the primordial plasma had a really small mean free path (= average distance between interacting with another particle), but as the universe expanded the mean free path increased until the photons decoupled (when the universe was around 400'000 years old if my memory is not cheating me) and have been traveling freely since then (until we measure them ;-) ).

Another consequence also seen in the CMB is that these photons decoupled having a temperature of about 3000K and the ones we measure today are at 2.725K. This is also due the the expansion because this expansion automatically increases the wavelength, which results in less energetic photons and hence lower temperature ones.

[lemit]

I guess you read too advanced theory, because then it is hard to understand ;-)

 

Anyway, yes, that is the way it seems to be. It is more more fun, the universe seems to be in accelerated expansion, which means the further you go away the quicker things (galaxies, galaxy-clusters,...) receede from us. But no wrong conclusions from here, this does not imply that we are at the center of the universe.

 

The expanding universe has also other consequences, it is the reason why we see the cosmic microwave background radiation (CMB or sometimes CMBR). Just after the bigbang the universe was so dense that the photons in the primordial plasma had a really small mean free path (= average distance between interacting with another particle), but as the universe expanded the mean free path increased until the photons decoupled (when the universe was around 400'000 years old if my memory is not cheating me) and have been traveling freely since then (until we measure them ;-) ).

Another consequence also seen in the CMB is that these photons decoupled having a temperature of about 3000K and the ones we measure today are at 2.725K. This is also due the the expansion because this expansion automatically increases the wavelength, which results in less energetic photons and hence lower temperature ones.

 

This might reflect the fact that I understand about half of that, but I'm curious: is the increase in the speed of expansion the further you get from the center reflective of the concept that the universe is expanding in all directions at the same time?

 

Thanks.

 

--lemit

[freeztar]

This might reflect the fact that I understand about half of that, but I'm curious: is the increase in the speed of expansion the further you get from the center reflective of the concept that the universe is expanding in all directions at the same time?

 

Thanks.

 

--lemit

 

Yes. :bdayhappy_balloons:

 

For example, if we look in any direction away from "center", everything seems to be moving away from us. The farther the object, the faster its movement. If we could instantly transport to a far away galaxy, we would see the same thing essentially. Everything would be expanding away from everything else.

 

It's important to note that this is a universe-level phenomena and does not really apply to local systems like our Solar System.

 

This wiki is decent and has some good links to other relevant wikis.

Metric expansion of space - Wikipedia, the free encyclopedia

[Time_Travel]

I guess you read too advanced theory, because then it is hard to understand ;-)

 

Anyway, yes, that is the way it seems to be. It is more more fun, the universe seem s to be in accelerated expansion, which means the further you go away the quicker things (galaxies, galaxy-clusters,...) receede from us. But no wrong conclusions from here, this does not imply that we are at the center of the universe.

 

The expanding universe has also other consequences, it is the reason why we see the cosmic microwave background radiation (CMB or sometimes CMBR). Just after the bigbang the universe was so dense that the photons in the primordial plasma had a really small mean free path (= average distance between interacting with another particle), but as the universe expanded the mean free path increased until the photons decoupled (when the universe was around 400'000 years old if my memory is not cheating me) and have been traveling freely since then (until we measure them ;-) ).

Another consequence also seen in the CMB is that these photons decoupled having a temperature of about 3000K and the ones we measure today are at 2.725K. This is also due the the expansion because this expansion automatically increases the wavelength, which results in less energetic photons and hence lower temperature ones.

 

 

OK now here is the standard theory i understand::

If Universe is expanding now it means that at one point it must have been so close together that everything including space,matter were all packed in one tight spot , and that tight spot was smaller than the atom(or equal to atom, don't remember exactly).

This forms the basis for the Big Bang correct?

[freeztar]

OK now here is the standard theory i understand::

If Universe is expanding now it means that at one point it must have been so close together that everything including space,matter were all packed in one tight spot , and that tight spot was smaller than the atom(or equal to atom, don't remember exactly).

This forms the basis for the Big Bang correct?

 

That's pretty much it, but understanding the implications of the BBT requires a step away from intuition when it comes to the "bang" part. Unlike our normal experience with seeing an object explode (fireworks, special fx, etc.), the universe did not explode into a time and space that was already there. Rather, its expansion created what we now know as time and space.

 

Using the raisin bread analogy, the raisons already have a defined space realtive to one another. As heat increases, they drift apart. The raisins on opposite sides of the bread see the greatest relative change in velocity. Distance makes it additive, but nothing can violate c within the confines of Relativity (which accurately explains physical phenomena on a universe scale).

[Time_Travel]

That's pretty much it, but understanding the implications of the BBT requires a step away from intuition when it comes to the "bang" part.

 

Using the raisin bread analogy, the raisons already have a defined space realtive to one another. As heat increases, they drift apart. The raisins on opposite sides of the bread see the greatest relative change in velocity. Distance makes it additive, but nothing can violate c within the confines of Relativity (which accurately explains physical phenomena on a universe scale).

 

 

 

OK now we pretty much agree with current matter and UNIVERSE being held in a small very small space.

 

When it exploded the time and space expanded. All agree with that again. Now when the matter and everything is held in a tiny atom , then with the bang the time and space expanded so did the matter right.

[sanctus]

Freez, about this violating c part. In my understanding actually it is possible that very far galaxies move quicker than c, without violating relativity. Simply if they have peculiar motion away from us and then you add the expansion of space-time you can get a higher than c speed.

I remeber reading a paper on this, and it made sense then, it went much deeper than what I remeber now.

[Time_Travel]

OK we all agree that the whole Universe before the Big Bang was in a very very small space may be even smaller than the atom.

 

Clearly right now i am bigger than an atom and my laptop is alos bigger than an atom.

So after the Big Bang The matter too expanded. Do you people agree with me on this???

[sanctus]

No, I do not really agree on the "whole universe before the BB", because then it is already hard to define before. For simplicity we can agree on that right after the BB the universe was really small.

 

For the rest, what do you mean by the matter expanded? That the for example size of a proton increased?

[freeztar]

Freez, about this violating c part. In my understanding actually it is possible that very far galaxies move quicker than c, without violating relativity. Simply if they have peculiar motion away from us and then you add the expansion of space-time you can get a higher than c speed.

I remeber reading a paper on this, and it made sense then, it went much deeper than what I remeber now.

 

Correct. Galaxies can be seen moving at an "apparent" velocity above c, but there's no violation of relativity.

[Time_Travel]

For simplicity we can agree on that right after the BB the universe was really small.

 

How Big the Universe might have been at the time of BB. Around the size of an atom?????

[Tormod]

How Big the Universe might have been at the time of BB. Around the size of an atom?????

 

At the time of the BB there was no matter. Thus there was no defined size for anything.

[Time_Travel]

At the time of the BB there was no matter. Thus there was no defined size for anything.

 

OK agreed no matter at all.

Immediately after the BB how big was that matterless universe?? around the size of an atom??

[sanctus]

The size is kind of hard to say, if one extrapolates just back in time what we see now, then one gets to a point (point=no size, just like a line has just 1 dimension, a point has only zero dimensions) with infinite density, temperature etc. But this is a singularity, hence we cannot extrapolate until then, because the law of physics we know break down there. See: Plank Epoch for example.

 

Actually, read through this. That gives a better idea than wiki.

 

And if you really want numbers it is believed that after 1 Planck time ([math]10^{-43}[/math] seconds) the universe had the size of a Planck length ([math]10^{-33}[/math] cm) which is even much smaler than an atom...

[Tormod]

OK agreed no matter at all.

Immediately after the BB how big was that matterless universe?? around the size of an atom??

 

Well - my point was that since there was no matter, there were no atoms. And thus there was nothing to compare the size of the universe to. Or we could assume that it had no size at all.

[Time_Travel]

 

Actually, read through this. That gives a better idea than wiki.

Thank's for the Link.

 

And if you really want numbers it is believed that after 1 Planck time ([math]10^{-43}[/math] seconds) the universe had the size of a Planck length ([math]10^{-33}[/math] cm) which is even much smaler than an atom...

 

So now the whole universe after 10^(-43) seconds it was created had the size of Planck length 10^(-33) cm , which is smaller than an atom.

 

Right now the fingers i am typing with contains trillions of atoms , and definitely my body size and the environment around me is bigger than the size of the Universe when it was 10^(-43 ) secs old. So matter too expanded with space time. If the answer is NO how can i be bigger than 10^(-33) cm????