Accelerating Universe Expansion’s Implications? (layman’s questions)

In summary: But it only applies to local regions of the universe. Anything moving away from us faster than the speed of light cannot exist.
  • #1
shawn-m
2
0
I’m new to these forums and as a matter of personal curiosity, and as someone who can’t follow the math behind the basic concepts, I have a few questions. The first set have to do with the accelerating expansion of our universe.

A) Does this acceleration affect the inflationary model of the universe, and is the universe younger than previously thought?

B) Has the rate of acceleration been determined? If so, how long before the speed of expansion greatly approaches the speed of light?

C) What happens when the speed of light is reached? Will all matter (even black holes?) convert to pure energy?

D) Who was the scientist that theorized that the universe’s accelerating expansion is fueled by an inverse property of gravity (a few years ago, I think). Where is she now and how has this theory faired? – Or has my memory really bungled this one?

Thanks for any response; hopefully these questions aren’t too embarrassingly stupid/ignorant, and I’m deeply sorry if I’m not bright enough to realize these questions were answered elsewhere. . .
 
Space news on Phys.org
  • #2
Welcome to PF shawn-m; these are all excellent questions! I'll answer what I can

shawn-m said:
A) Does this acceleration affect the inflationary model of the universe, and is the universe younger than previously thought?
I don't know the details to this question. There is definitely some effect; I think its actually fairly subtle however, as the current accelerated expansion, and inflation soon after the big-bang are fairly separate concepts.

shawn-m said:
B) Has the rate of acceleration been determined? If so, how long before the speed of expansion greatly approaches the speed of light?
Yes and no. There are measurements for the rate of expansion; their uncertainties are very large (only recently is the community convinced that the expansion is accelerating at all. There are other measurements which directly relate (i.e. the matter/energy content of the universe, properties of the cosmic microwave background, etc), I'm not sure how they can be used to determine the value of the acceleration however.

shawn-m said:
C) What happens when the speed of light is reached? Will all matter (even black holes?) convert to pure energy?
This is the most important question---and it shows that you're a little confused (understandably!). Every point in space is expanding (moving away) from every other point in space. Like the surface of a balloon as its being filled with air (note this is not "inflation"). The farther away two points are from each other, the faster they are moving relative to each-other (related by http://en.wikipedia.org/wiki/Hubble%27s_law" [Broken]). Right now, there are parts of the universe which are moving away from us at speeds larger than the speed of light. The distance at which the average relative velocity is the same as the speed of light, is called the 'horizon' of the universe. There's nothing special about it, except that we'll never know-about, or interact-with, what's outside of it.

We're all taught that 'nothing can exceed the speed of light'. This is true---but it only applies to local regions of the universe.

shawn-m said:
D) Who was the scientist that theorized that the universe’s accelerating expansion is fueled by an inverse property of gravity (a few years ago, I think). Where is she now and how has this theory faired? – Or has my memory really bungled this one?
I'm not sure who you're referring to, but I believe the first person to come up with the idea was Einstein, in his famous 'http://en.wikipedia.org/wiki/Cosmological_constant" [Broken]'. But I might be confused about what you're asking.
 
Last edited by a moderator:
  • #3
zhermes said:
Right now, there are parts of the universe which are moving away from us at speeds larger than the speed of light.

Generally I follow what you're saying, but the line above sounds too assertive. An inherently infinite and unbounded universe might be mathematically consistent, but it is just as fair to say that anything moving away from us faster than the speed of light cannot exist (as far as we are concerned, of course).

The distance at which the average relative velocity is the same as the speed of light, is called the 'horizon' of the universe.

Would it be correct to say that this horizon is 300,000 lyr beyond the CMB?
 
  • #4
Bob, Shawn, Hermes. What Hermes says here is right:
==quote Hermes==
...Every point in space is expanding (moving away) from every other point in space. Like the surface of a balloon as its being filled with air (note this is not "inflation"). The farther away two points are from each other, the faster they are moving relative to each-other (related by http://en.wikipedia.org/wiki/Hubble%27s_law" [Broken]). Right now, there are parts of the universe which are moving away from us at speeds larger than the speed of light. ...
We're all taught that 'nothing can exceed the speed of light'. This is true---but it only applies to local regions of the universe.
==endquote==

In uniform expansion of distances nobody gets anywhere.
It's not like ordinary motion. In ordinary motion there can in principle be some object you depart from and some object you approach. At least in principle you can be getting farther from something and closer to something else.

There is no law of physics that says that distances cannot expand at rates exceeding the speed of light. That is not ordinary motion and it doesn't violate special relativity. Special Rel does not even apply to the changing largescale geometry of General Rel. Special Rel (where you are taught the speed limit for ordinary motion) uses fixed static geometry which applies only locally, in patches of the real universe which are small enough so expansion effects can be ignored.
 
Last edited by a moderator:
  • #5
Hermes, here is something for you to try. Google "cosmos calculator" which will get you
http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html

The link is also in my signature.

The standard cosmology model is built into this calculator. You first need to type in three numbers (the basic parameters of the model).

.27 and .73 and 71, for "matter density" "cosmological constant" and "Hubble parameter".

Then put in 1.7 for the redshift and see what you get.

Most of the galaxies we are observing today have redshifts which are equal or greater than 1.7. Lots have redshifts like 5, or 6, or even 7...
The CMB has redshift about 1090 or approximately 1100.

So most stuff that we can see and are currently seeing, the distance from here to there was already expanding faster than c when the light was emitted. And is expanding faster than c to this day. Notice that I did not say "moving".
I said the distances are changing. Dynamic geometry. Curved spacetime means dynamic spatial geometry. There is something important to realize when one is ready, that this calculator example with redshift 1.7 can help realize.

You should have questions, like "how does the light get here" if the recession rates then and now were > c.

The "charley" link in my signature can help with that. The first page is blank so scroll down. It is a SciAm reprint by Charley Lineweaver and Tamara Davis. But you can ask questions here too. But I suggest you try various redshifts in the calculator, first, and see what recession rates you get. A rate of recession is not necessarily to be thought of as a speed of ordinary motion (though people will say "recession speed" blurring the distinction).

I want to thank you for the good answers you have been giving people. I realize you know a lot of this stuff and may have played around with cosmology calculators before. I differ with you on minor points about the various "horizons" (of which there are several in cosmology) but this does not matter.
 
  • #6
Wow, folks! Thanks for the answers!

This nicely went to the heart of the matter, and was explained in such a way that I finally get it.
 
  • #7
marcus said:
Hermes, here is something for you to try. Google "cosmos calculator" which will get you http://www.uni.edu/morgans/ajjar/Cosmology/cosmos.html
I haven't seen one of these before, really cool--thanks!

marcus said:
So most stuff that we can see and are currently seeing, the distance from here to there was already expanding faster than c when the light was emitted. And is expanding faster than c to this day. [...] The "charley" link in my signature can help with that.
I never realized that before; also, very cool. And I indeed had exactly that question, and the article answered it quite nicely (in addition to suggesting what you meant by 'various horizons'). Thanks again!

marcus said:
I want to thank you for the good answers you have been giving people.
Really appreciate that, its my pleasure to give an occasionally-correct answer.
 

1. What is the accelerating expansion of the universe?

The accelerating expansion of the universe refers to the observation that the rate at which the universe is expanding is increasing over time. This means that galaxies and other objects in the universe are moving away from each other at a faster and faster rate.

2. What are the implications of an accelerating universe expansion?

The implications of an accelerating universe expansion are still being studied and are not yet fully understood. However, one potential implication is that the expansion may continue indefinitely, leading to a "big freeze" scenario where the universe becomes increasingly sparse and cold. Another potential implication is that the expansion may eventually reverse, leading to a "big crunch" where the universe collapses back in on itself.

3. How do we know that the universe is expanding at an accelerating rate?

Scientists have been able to measure the expansion of the universe by observing the redshift of distant galaxies. This redshift is caused by the stretching of light as it travels through expanding space. By measuring the redshift of galaxies at different distances, scientists have been able to determine that the rate of expansion is increasing over time.

4. What is dark energy and how does it relate to the accelerating universe expansion?

Dark energy is a mysterious force that is thought to be responsible for the accelerating expansion of the universe. It is believed to make up about 70% of the total energy in the universe, but its exact nature is still unknown. Some theories suggest that dark energy is a property of space itself, causing it to expand at an accelerated rate.

5. Will the accelerating universe expansion have any direct impact on Earth or our daily lives?

No, the accelerating expansion of the universe is not expected to have any direct impact on Earth or our daily lives. The expansion is happening on a cosmic scale and is not noticeable on human timescales. However, studying the implications of this expansion can give us a better understanding of the universe and our place in it.

Similar threads

Replies
23
Views
1K
Replies
19
Views
2K
Replies
3
Views
1K
Replies
13
Views
1K
Replies
5
Views
1K
  • Cosmology
Replies
17
Views
2K
  • Cosmology
Replies
4
Views
1K
  • Cosmology
Replies
1
Views
873
  • Special and General Relativity
Replies
4
Views
426
Back
Top