A question about the age of "toddler" universe

[jadey]

The distance now will be greater than 13.7GLY, but not because of inflation. Inflation is a specific phase of the BB and it occurred very early on (in the first second, IIRC). It also increased the size of the universe by many orders of magnitude (28?, 34?).

The distance will have increased due to the expansion of space. the space between Earth and the remote galaxy has got bigger -- neither Earth nor the galaxy has moved through space to get farther apart. By 'Earth' I mean the stuff that ended up being the Milky Way, as it was somewhat different 13.7GYA.

It is my understanding that inflation is a term for the expansion of space, and that the very early universe experienced exponential inflation. I also thought that we were still in a period of inflation, albeit rather small. The definitions of inflation I find on the web don't seem to confirm my understanding.

Is there another term that refers to the expansion of space?

 

[edd]

It is my understanding that inflation is a term for the expansion of space, and that the very early universe experienced exponential inflation. I also thought that we were still in a period of inflation, albeit rather small. The definitions of inflation I find on the web don't seem to confirm my understanding.

Is there another term that refers to the expansion of space?

Inflation refers to a specific kind of accelerating expansion. There can also be decelerating expansion, which is not inflation at all.

As has been said, very early on we think the universe went through really extreme accelerating expansion, and became orders of magnitudes bigger in timescales like a second, or something crazily short.

We have recently reentered a phase of accelerating expansion (recently being some considerable fraction of the age of the universe) but that is much slower. The universe hasn't grown by anything like one order of magnitude in that time, and it's not accelerating all that fast, so it's very different from early universe inflation.

As the current accelerating expansion is so very different from the early expansion, a cosmologist hearing the word 'inflation' will almost exclusively think of the early universe kind, not the current late kind, which will generally just be referred to as 'accelerating expansion' or some other broadly equivalent term (maybe 'lambda-dominated era' or something like that, to refer to the fact that it's when the cosmological constant or dark energy - lambda - is the major amount of energy in the universe).

They're not without similarities, but they're not generally thought of as the same kind of thing.

 

[jadey]

Inflation refers to a specific kind of accelerating expansion. There can also be decelerating expansion, which is not inflation at all.

As has been said, very early on we think the universe went through really extreme accelerating expansion, and became orders of magnitudes bigger in timescales like a second, or something crazily short.

We have recently reentered a phase of accelerating expansion (recently being some considerable fraction of the age of the universe) but that is much slower. The universe hasn't grown by anything like one order of magnitude in that time, and it's not accelerating all that fast, so it's very different from early universe inflation.

As the current accelerating expansion is so very different from the early expansion, a cosmologist hearing the word 'inflation' will almost exclusively think of the early universe kind, not the current late kind, which will generally just be referred to as 'accelerating expansion' or some other broadly equivalent term (maybe 'lambda-dominated era' or something like that, to refer to the fact that it's when the cosmological constant or dark energy - lambda - is the major amount of energy in the universe).

They're not without similarities, but they're not generally thought of as the same kind of thing.

Thanks for the explanation. It seems I had the general concepts correct, just not the terminology.

 

[jadey]

The distance will have increased due to the expansion of space. the space between Earth and the remote galaxy has got bigger -- neither Earth nor the galaxy has moved through space to get farther apart. By 'Earth' I mean the stuff that ended up being the Milky Way, as it was somewhat different 13.7GYA.

Are you saying that all of the increased distance between galaxies is due to space expansion? Are Hubble's observations of the recessional velocities of distant galaxies explained entirely by the expansion of space, or is it a combination of that and galaxies travelling through space?

 

[nathan]

Are you saying that all of the increased distance between galaxies is due to space expansion? Are Hubble's observations of the recessional velocities of distant galaxies explained entirely by the expansion of space, or is it a combination of that and galaxies travelling through space?

I am not a cosmologist, but yes -- space expands, objects are not traveling through it. If the recessional velocities were caused by objects traveling through space, where v = H₀D, for big enough D, v > c (if you want a mixture of space expansion and object translation, you're just changing the effective H₀). Special Relativity has something to say about that.

 

[edd]

Are you saying that all of the increased distance between galaxies is due to space expansion? Are Hubble's observations of the recessional velocities of distant galaxies explained entirely by the expansion of space, or is it a combination of that and galaxies travelling through space?

Galaxies do travel through space, but not in a coherent way on the largest scales. The motion through space on top of the cosmological effect ('peculiar velocity') causes a scatter in the relation between redshift and distance, but at cosmological scales almost all the redshift comes from the expansion of space, and almost all the distance comes from cosmological expansion.

It does lead to some odd effects at times though, notably the 'Fingers of God' and the Kaiser Effect, which you can google