[neilep (OP)]

Hello,


As a sheepy I of course know all about inflation...well, the inflation of my belly....but what I really would like to know is the speed of the really fast bit of the expansion thing...apparently it was faster than light or sound or a Ferrari SF90 !!...or something.


As we all know the Universe was invented in 1792 by Saganaski Carloff. He hooked up the quantum dot thingy to his airbed pump and voila !...the Universe was born.


As a firm believer in empirical study I went back in time with my trusty stopwatch/Abacus and measured the speed of that expanse thing as two apples and a banana !.....well...I can't convert that into adult time and so ...no luck there !






Me Timing the Expanse Thing Just 13.8 billion years ago !! (Last Tuesday)




So, Can EWE tell me...How fast was the faster than light expansion ?




Best Wishes and super hugs


Sheepy
xxxxx

[paul cotter]

Inflation is generally caused by bad monetary policy, the Weimar republic being an excellent example for study (SORRY!!). That is an interesting question ewe have posed and I don't know the answer. If one could imagine the leading edge of the expansion then it is difficult to determine it's speed as there is nothing at all, not even space beyond it and the material/space behind it is also expanding rapidly- without some reference point from which to measure the speed it is a difficult to state the speed. In all likelihood there is no leading edge as this a concept associated with the boundary between two volumes and in this case there is only one volume. It is difficult to conceive an expansion into nothing. These are my muddled thoughts on the matter, I'm sure there will be some better answers.

[Halc]

How fast was the faster than light expansion ?

Expansion isn't a speed, and hence cannot be meaningfully compared to one.
Speed has units of something list distance/time, but expansion has units of distance/time/distance.

So 300000 km/sec is a speed (c), but ~70 km/sec/megaparsec is our current expansion rate (Hubble's constant, which isn't a constant), which is different units entirely and thus cannot be compared with a speed like c.

That said, it has taken about 7 billion years to expand to where we are now from when the distances were half of what they are now.  During the inflation epoch, any region of space doubled in size not every 7 billion years, but every 10^-64 seconds, and it kept it up for quite a while so that the portion of what is now our visible universe grew from an indescribably small dot to about the size of a grapefruit.  At that point, inflation quit and normal universe expansion took over, with nearby visible universes receding from us at more or less the same rate as they are today.

[evan_au]

For some more information:
https://en.wikipedia.org/wiki/Cosmic_inflation
https://en.wikipedia.org/wiki/Inflationary_epoch

[paul cotter]

I am making one small addition to what Halc has said: expansion has the dimensions of 1/T and units of 1/s, ie it is the reciprocal of time.

[Kryptid]

During the inflation epoch, any region of space doubled in size not every 7 billion years, but every 10-64 seconds

So if I'm doing the math right, even two points that were a Planck length apart would have had a relative recession velocity of about 5.39 x 10^20 times faster than the speed of light...

[Halc]

During the inflation epoch, any region of space doubled in size not every 7 billion years, but every 10^-64 seconds

So if I'm doing the math right, even two points that were a Planck length apart would have had a relative recession velocity of about 5.39 x 10^20 times faster than the speed of light...

You didn't show the math, so I cannot suggest a higher or lower value, but it seems there is way too little information in the quip I posted to come up with a figure like that, especially to 3 digits of precision.
That recession rate corresponds to an object currently 7.7 x 10²⁹ light years away, but that has nothing to do with the exponential expansion going on during the inflation epoch.

The expansion rate will eventually approach exponential again at a rate of about 55 km/sec/mpc, but this close to the point where dark energy took over, it's been fairly linear for a while, meaning a typical distant object has been receding from us at a rate that hasn't changed a whole lot in the last ~9 billion years. That will change more noticeably as time continues on.


First post in 45 days Kryptid, where you been?

[Kryptid]

All right, here's the math I did:

I assumed when you spoke of a region of space doubling, you were talking about distances (as opposed to volume). So if I have two points that start out 1 Planck length apart (1.616 x 10^-35 m), and the expansion of space in a period of 10^-64 s causes the distance between those two points to double (to 3.232 x 10^-35 m), then the distance between those two points increased by 1 Planck length over a period of 10^-64 seconds. Speed is distance divided by time, so (1.616 x 10^-35 m)/(10^-64) = 1.616 x 10²⁹ m/s. The speed of light is 299,792,458 m/s, so (1.616 x 10²⁹ m/s)/(299,792,458 m/s) = 5.39 x 10²⁰ times the speed of light.

Well, this past week and a half, I've been sick with the flu. Before that, I guess I just haven't seen threads that piqued my interest too much.

[Halc]

So if I have two points that start out 1 Planck length apart (1.616 x 10^-35 m), and the expansion of space in a period of 10^-64 s causes the distance between those two points to double (to 3.232 x 10^-35 m), then the distance between those two points increased by 1 Planck length over a period of 10^-64 seconds. Speed is distance divided by time, so (1.616 x 10^-35 m)/(10^-64) = 1.616 x 10²⁹ m/s. The speed of light is 299,792,458 m/s, so (1.616 x 10²⁹ m/s)/(299,792,458 m/s) = 5.39 x 10²⁰ times the speed of light.

Well that's one Planck length every 10^-64 s, which is linear speed, not exponential speed. Were my figure correct, the final speed would be around 10³² times faster than that.
So let's start over. The 10^-64 s figure comes from the most reliable source of "I remember reading somewhere".  So forget that. Also forget the 3 digits of precision since -1 digits is already asking way too much.  I went to wiki where no mention of the exponential rate is made, but it can be worked out, and I presume the numbers there reflect the current state better than "I read somewhere".

Looking at https://en.wikipedia.org/wiki/Chronology_of_the_universe page, we read that inflation took place from 10^-36 s to 10^-32 s.  If a tick is 10^-36 s, it lasted from the end of tick one through to tick 10000, which is pretty much the entire history up to that point, so we can say it started at zero instead of 1.

That page also says that during those 10000 ticks, the universe expanded by a factor of around 10²⁶ which is about 2⁸⁷ which means it doubled 87 times in 10000 ticks, or once every 115 ticks which is WAAAAY slower than once every 10^-64 seconds, but still exponential.  It comes to somewhere around 10^-34 sec per doubling.

So now we can calculate how fast our two points of space recede from each other by the end of inflation.  We start with a Planck length of 3x10^-35 meters and expand that 10²⁶ times to a final separation of 3x10^-9 meters which is about 3 nm. At this point the separation is growing at about 2nm per tick.  Multiply that rate by 10³⁴ and you get 2x10²⁵ m/sec which is about 10¹⁷c, about 5000, about half a million times slower than the figure you mentioned.  That's during inflation. How about now?

Given that after inflation, what is the space included in our visible universe (100 GLY diameter) was the size of a grapefruit. (Source: "I read somewhere", so appreciate a better source)
A grapefruit is perhaps 0.15m.
If that is true, the 3 nm is 1/50 millionth of that distance.  100 GLY / 50m is 2000LY, which is about 2% the diameter of our fairly large galaxy, meaning the space currently occupied by our galaxy was squished into a disk of diameter 50 Planck lengths near the end of the grand unification epoch.

As for expansion rate, current expansion is 70 m/sec/mpc.  2000 LY is about .0006 mpc, so 70*.0006 = 4 cm per second, considerably slower than the 10¹⁵c it was doing just before inflation ended.


Let me know if I messed up and missed 20 zeroes or something. All that was done mostly in my head and in sort of haste. Peer review is encouraged.

[set fair]

One posibility is that prior to inflation, the universe could be described in terms of the fundamental units we use today; except the list of units. which described / were needed to describe, the very early universe didn't include the meter. ie there was no length, distance, volume or velocity etc until what there was decayed into particles which needed units of length to describe them. If it were like that then inflation could be thought of  as the emergence of space.

This is speculative but so is everything else put forward to explain inflation because we don't know how it happened.