geordief Posted July 28, 2022 Share Posted July 28, 2022 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? Link to comment Share on other sites More sharing options...
Bufofrog Posted July 28, 2022 Share Posted July 28, 2022 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?). 1 Link to comment Share on other sites More sharing options...
geordief Posted July 28, 2022 Author Share Posted July 28, 2022 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. Link to comment Share on other sites More sharing options...
MigL Posted July 28, 2022 Share Posted July 28, 2022 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. Link to comment Share on other sites More sharing options...
Bufofrog Posted July 28, 2022 Share Posted July 28, 2022 I think this wiki article is pretty helpful for explaining the acceleration: expanding universe. Link to comment Share on other sites More sharing options...
geordief Posted July 28, 2022 Author Share Posted July 28, 2022 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? Link to comment Share on other sites More sharing options...
MigL Posted July 28, 2022 Share Posted July 28, 2022 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. Link to comment Share on other sites More sharing options...
Airbrush Posted August 14, 2022 Share Posted August 14, 2022 (edited) "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 August 14, 2022 by Airbrush Link to comment Share on other sites More sharing options...
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