7 ms·

Here's a narrated video about this current cosmological crisis: https://www.youtube.com/watch?v=0sfvQ_fsil4 https://www.youtube.com/watch?v=0sfvQ_fsil4 This is

Here's a narrated video about this current cosmological crisis: https://www.youtube.com/watch?v=0sfvQ_fsil4 https://www.youtube.com/watch?v=0sfvQ_fsil4 This is one of the key graphics: https://i0.wp.com/particlebites.com/wp-content/uploads/2020/01/hubble_tension.png https://i0.wp.com/particlebites.com/wp-content/uploads/2020/...

doublepg23 6y ago
This was an excellent video, thank you. PBS Spacetime also did a video: https://youtu.be/72cM_E6bsOs https://youtu.be/72cM_E6bsOs
burlesona 6y ago
Thanks for sharing! Seems like a good video but I don’t really enjoy long-form video... any relevant articles or written media describing the same thing?
- ngcc_hk 6y ago
  Agree as video takes too long
dheera 6y ago
The biggest "concern" I have about the expanding universe is that although I have a lot of hope for interstellar travel at some point in the coming few millenia, intergalactic travel poses a whole another set of impossibilities to face, that I'm worried it will never be possible. The space between galaxies is pretty devoid of anything you can use as fuel, repair materials, or anything else. That space is expanding, and at some point around 100-150 billion years from now, galaxies that are not gravitationally bound to the Local Group will be no longer reachable or observable [1]. You need ten times the mass of Mt. Everest in e=mc^2 energy (i.e. 100% efficiency) per 1 kg of mass to get to Andromeda at 1g acceleration/deceleration. [0] For this reason I sincerely hope that conservation of mass/energy is not necessarily true. Nothing says it needs to be true other than that it empirically seems to be the case, and there is no known process that violates it, other than the Big Bang itself. If it can be violated, we have hope for the long long long term future. Scary to think about this stuff. [0] https://en.wikipedia.org/wiki/Intergalactic_travel https://en.wikipedia.org/wiki/Intergalactic_travel [1] https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future
- type_enthusiast 6y ago
  Well, that puts some perspective on 2020. I mean, it's bleak perspective, but surely if we all write to our congressperson we can act now to prevent the heat death of the universe, right?
- tzs 6y ago
  Energy isn’t really conserved in general relativity. See this Sean Carroll article for more (1). I don’t think this helps with your concerns, though. (1) https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
- bouncycastle 6y ago
  However, after the universe finishes expanding, wouldn't it start contracting again? Btw, Andromeda will collide with the Milky Way in about 4 billion years, so at least we won't need ten times the mass of Mt. Everest to get there...
  - macintux 6y ago
    > However, after the universe finishes expanding, wouldn't it start contracting again? Unless the answer has changed in the last several years, no, the consensus is that it's expanding too fast and has too little mass (and thus gravity) to collapse again. (Disclaimer: not even an amateur at this, at least not for 40 years.)
  - throwaway201103 6y ago
    If you subscribe to Roger Penrose's theory, at the point of infinite expansion, the current "Aeon" will end and a new big bang will happen. As best I understand it, at the point of infinite expansion, there are only photons. Mass no longer exists therefore scale no longer exists. So an infinitely huge universe becomes indistinguishable from an infinitely small universe.
    - tokamak-teapot 6y ago
      What causes the Big Bang in this scenario?

doublepg23 6y ago

This was an excellent video, thank you. PBS Spacetime also did a video: https://youtu.be/72cM_E6bsOs https://youtu.be/72cM_E6bsOs

burlesona 6y ago

Thanks for sharing! Seems like a good video but I don’t really enjoy long-form video... any relevant articles or written media describing the same thing?

ngcc_hk 6y ago
Agree as video takes too long

dheera 6y ago

The biggest "concern" I have about the expanding universe is that although I have a lot of hope for interstellar travel at some point in the coming few millenia, intergalactic travel poses a whole another set of impossibilities to face, that I'm worried it will never be possible. The space between galaxies is pretty devoid of anything you can use as fuel, repair materials, or anything else. That space is expanding, and at some point around 100-150 billion years from now, galaxies that are not gravitationally bound to the Local Group will be no longer reachable or observable [1]. You need ten times the mass of Mt. Everest in e=mc^2 energy (i.e. 100% efficiency) per 1 kg of mass to get to Andromeda at 1g acceleration/deceleration. [0] For this reason I sincerely hope that conservation of mass/energy is not necessarily true. Nothing says it needs to be true other than that it empirically seems to be the case, and there is no known process that violates it, other than the Big Bang itself. If it can be violated, we have hope for the long long long term future. Scary to think about this stuff. [0] https://en.wikipedia.org/wiki/Intergalactic_travel https://en.wikipedia.org/wiki/Intergalactic_travel [1] https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future

type_enthusiast 6y ago
Well, that puts some perspective on 2020. I mean, it's bleak perspective, but surely if we all write to our congressperson we can act now to prevent the heat death of the universe, right?
tzs 6y ago
Energy isn’t really conserved in general relativity. See this Sean Carroll article for more (1). I don’t think this helps with your concerns, though. (1) https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
bouncycastle 6y ago
However, after the universe finishes expanding, wouldn't it start contracting again? Btw, Andromeda will collide with the Milky Way in about 4 billion years, so at least we won't need ten times the mass of Mt. Everest to get there...
- macintux 6y ago
  > However, after the universe finishes expanding, wouldn't it start contracting again? Unless the answer has changed in the last several years, no, the consensus is that it's expanding too fast and has too little mass (and thus gravity) to collapse again. (Disclaimer: not even an amateur at this, at least not for 40 years.)
- throwaway201103 6y ago
  If you subscribe to Roger Penrose's theory, at the point of infinite expansion, the current "Aeon" will end and a new big bang will happen. As best I understand it, at the point of infinite expansion, there are only photons. Mass no longer exists therefore scale no longer exists. So an infinitely huge universe becomes indistinguishable from an infinitely small universe.
  - tokamak-teapot 6y ago
    What causes the Big Bang in this scenario?