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Does cosmic expansion ever end?


geordief
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I have learned that the  rate at which the galaxies are receding  from each other is accelerating.

(Quite the surprise when this was discovered  ,I seem to recall)

 

So we have an ongoing acceleration of the recessionary  process.

Is there any way to quantify this acceleration and so determine  whether this acceleration itself is constant  or whether it could be slowing down ?(or even speeding up)

 

I think the mathematical  term is "jerk"

Could the jerk be negative and how could we know?

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3 minutes ago, geordief said:

Is there any way to quantify this acceleration and so determine  whether this acceleration itself is constant  or whether it could be slowing down ?(or even speeding up)

The acceleration is speeding up.

"Does cosmic expansion ever end?"

It doesn't look like it will ever end (but who is to say for sure?).

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3 hours ago, Bufofrog said:

The acceleration is speeding up.

"Does cosmic expansion ever end?"

It doesn't look like it will ever end (but who is to say for sure?).

How did they measure that the actual  acceleration was accelerating?

 

It sounds very hard to me.

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The 'error bars' on the rate of recession are large enough as to make determining the change in recession rate very difficult ( and possibly still ambiguous ) due to the large numbers of extremely distant observations, where distance scales could still be in question.

Now you want to know the rate of change of the changing rate of recession, or acceleration of the acceleration ?

I don't think anyone knows that, but they do know that recession rate wasn't always accelerating, so, while not quantified yet, there has obviously been a change.

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9 minutes ago, MigL said:

The 'error bars' on the rate of recession are large enough as to make determining the change in recession rate very difficult ( and possibly still ambiguous ) due to the large numbers of extremely distant observations, where distance scales could still be in question.

Now you want to know the rate of change of the changing rate of recession, or acceleration of the acceleration ?

I don't think anyone knows that, but they do know that recession rate wasn't always accelerating, so, while not quantified yet, there has obviously been a change.

So it seems possible (ie not ruled out) that the acceleration could come to a halt  and become negative ,leading to a big Crunch -even though, as I understood   it at the time the big Crunch  idea fell out of favour  when the accelerating expansion was first observed.

Is that fair?

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We don't really know the mechanism for accelerated expansion, as dark energy is still 'dark', so making guesses as to how it would change, if at all, in the future is pointless.

Nor are we sure that the 'standard candle' ( type 1A supernova, when a white dwarf star accretes enough material from a companion star to initiate carbon burning in its core, resulting in an explosion of known luminosity ) is accurate enough to set our distance scale.

All we know is that measurements of the Hubble Constant seem to have an increasing slope, indicating an acceleration of recession speeds.

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  • 3 weeks later...

"Does cosmic expansion ever end?"

From the way it looks in this region of the multiverse, it doesn't ever end.  All matter and black holes will evaporate into low-energy photons before expansion ends.

Edited by Airbrush
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