4 ms·

Actually it might. If expansion accelerates indefinitely, which is one of the theories, then eventually expansion will be stronger than the binding force of ato

Actually it might. If expansion accelerates indefinitely, which is one of the theories, then eventually expansion will be stronger than the binding force of atoms and then sub-atomic particles. This is called the "Big Rip". https://en.wikipedia.org/wiki/Big_Rip https://en.wikipedia.org/wiki/Big_Rip

rendall 6y ago
Oh! Well then. Thanks for pushing back. I learned something new today.
raattgift 6y ago
We have lots of observations of spiral galaxies at ever-increasing redshifts, and they don't look very different at different times -- closer galaxies are not collapsing more slowly than the distant ones. We also have good views of the Lyman-alpha forest through galaxy clusters at different redshifts, and the distribution of the spectral lines are another line of evidence that members of galaxy clusters closer to us have smaller radial components in their peculiar velocities than those at higher redshift/smaller angle/lower brightness. To get to a big rip you have to impose a further time derivative and figure out how to keep it small now and make it big later. AFAIK nobody who has tried this has avoided significant complexity to match the observational data we have today, except by pushing the Big Rip so enormously far into the future that we don't have enough data to constrain that future. The wikipedia article refers to WMAP9, which ended 2013 (~ 9 years after WMAP turned on in 2003). There is more recent data from Planck and other observatories, and they make it harder and harder to justify a Big Rip for the reasons half-admitted in the "Observed universe" section of that wikipedia article. Moreover, MESSENGER and other spacecraft sent to parts of our solar system have given us a lot of data about the metric of our solar system, and it is non-expanding; orbiting clocks support this more locally. Likewise, there are plenty of sensitive terrestrial experiments that highly constrain any expansion term in plausible Standard Model + gravity Lagrangians. It can't be ruled out but it has been effectively pushed back so far that it's the least of our worries about "what happens hundreds of trillions of years in the future" : if one accepts there there is a Big Rip field, there's no compelling reason why it should have significant effects on matter in the local group that soon, and several arguments about why it shouldn't. You'll find a bit more substance (and higher difficulty) at https://en.wikipedia.org/wiki/Quintessence_(physics)#Tracker_behavior https://en.wikipedia.org/wiki/Quintessence_(physics)#Tracker...
- rendall 6y ago
  Thanks for this

rendall 6y ago

Oh! Well then. Thanks for pushing back. I learned something new today.

raattgift 6y ago

We have lots of observations of spiral galaxies at ever-increasing redshifts, and they don't look very different at different times -- closer galaxies are not collapsing more slowly than the distant ones. We also have good views of the Lyman-alpha forest through galaxy clusters at different redshifts, and the distribution of the spectral lines are another line of evidence that members of galaxy clusters closer to us have smaller radial components in their peculiar velocities than those at higher redshift/smaller angle/lower brightness. To get to a big rip you have to impose a further time derivative and figure out how to keep it small now and make it big later. AFAIK nobody who has tried this has avoided significant complexity to match the observational data we have today, except by pushing the Big Rip so enormously far into the future that we don't have enough data to constrain that future. The wikipedia article refers to WMAP9, which ended 2013 (~ 9 years after WMAP turned on in 2003). There is more recent data from Planck and other observatories, and they make it harder and harder to justify a Big Rip for the reasons half-admitted in the "Observed universe" section of that wikipedia article. Moreover, MESSENGER and other spacecraft sent to parts of our solar system have given us a lot of data about the metric of our solar system, and it is non-expanding; orbiting clocks support this more locally. Likewise, there are plenty of sensitive terrestrial experiments that highly constrain any expansion term in plausible Standard Model + gravity Lagrangians. It can't be ruled out but it has been effectively pushed back so far that it's the least of our worries about "what happens hundreds of trillions of years in the future" : if one accepts there there is a Big Rip field, there's no compelling reason why it should have significant effects on matter in the local group that soon, and several arguments about why it shouldn't. You'll find a bit more substance (and higher difficulty) at https://en.wikipedia.org/wiki/Quintessence_(physics)#Tracker_behavior https://en.wikipedia.org/wiki/Quintessence_(physics)#Tracker...

rendall 6y ago
Thanks for this