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That's an interesting idea. I knew the universe is expanding relative to galaxies, but I didn't realize that the expansion of the universe was overcoming gravit

by bdamm 9y ago

That's an interesting idea. I knew the universe is expanding relative to galaxies, but I didn't realize that the expansion of the universe was overcoming gravity within the scope of a galaxy. Does this also mean that the distance between planets within a solar system will increase? Is the rate of expansion more than or less than the expansion of the sun's diameter? Does this mean that the distance from the Earth to the moon is increasing, and does it mean the planet itself is expanding? Is the expansion of the universe a destabilizing effect on orbital mechanics?

ajross 9y ago
The dark energy phenomenon driving accelerated expansion is poorly described by theory, so predictions don't mean much. But yes: if expansion continues accelerating as it has been then eventually it will overpower intra-galaxy gravitation, then intra-system, and eventually intra--celestial-bodies and so on. Eventually planets and stars (and atoms and protons!) would be ripped apart.
- pdonis 9y ago
  > if expansion continues accelerating as it has been then eventually it will overpower intra-galaxy gravitation, then intra-system, and eventually intra--celestial-bodies and so on. Eventually planets and stars (and atoms and protons!) would be ripped apart This is not true for dark energy, i.e., for accelerated expansion per se. It is only true for a "Big Rip" scenario in which the acceleration itself accelerates. The "stuff" that drives such a scenario is called "phantom energy" and such a scenario is currently believed to be extremely low probability.
Santosh83 9y ago
IIRC the expansion is accelerating according to the best observations. Which means in the far future galaxies should find themselves in an endless sea of voids. Eventually stars, planets, living beings and atoms will all get torn apart unless something counters the accelerating expansion.
- pdonis 9y ago
  > Eventually stars, planets, living beings and atoms will all get torn apart unless something counters the accelerating expansion. See my reply to ajross. Dark energy is not the same as a "Big Rip" scenario, which is what you are describing.
  - Santosh83 9y ago
    Thanks for the correction.
pavel_lishin 9y ago
As far as I know, the Sun will be long gone by the time that level of expansion is reached; at best, it'll be a tiny white dwarf, having long ceased its expansion. It can really be described as a problem that doesn't concern humanity, because by the time it hits, we won't be recognizably human anymore :P
pdonis 9y ago
> I didn't realize that the expansion of the universe was overcoming gravity within the scope of a galaxy. It isn't, at least not according to our best current models, which do not involve a "Big Rip" scenario. See my replies to others downthread. > Does this also mean that the distance between planets within a solar system will increase? Does this mean that the distance from the Earth to the moon is increasing, and does it mean the planet itself is expanding? Is the expansion of the universe a destabilizing effect on orbital mechanics? According to our best current models (i.e., in the absence of a "Big Rip"), no to all of these.

by bdamm 9y ago

ajross 9y ago

The dark energy phenomenon driving accelerated expansion is poorly described by theory, so predictions don't mean much. But yes: if expansion continues accelerating as it has been then eventually it will overpower intra-galaxy gravitation, then intra-system, and eventually intra--celestial-bodies and so on. Eventually planets and stars (and atoms and protons!) would be ripped apart.

pdonis 9y ago
> if expansion continues accelerating as it has been then eventually it will overpower intra-galaxy gravitation, then intra-system, and eventually intra--celestial-bodies and so on. Eventually planets and stars (and atoms and protons!) would be ripped apart This is not true for dark energy, i.e., for accelerated expansion per se. It is only true for a "Big Rip" scenario in which the acceleration itself accelerates. The "stuff" that drives such a scenario is called "phantom energy" and such a scenario is currently believed to be extremely low probability.

Santosh83 9y ago

IIRC the expansion is accelerating according to the best observations. Which means in the far future galaxies should find themselves in an endless sea of voids. Eventually stars, planets, living beings and atoms will all get torn apart unless something counters the accelerating expansion.

pdonis 9y ago
> Eventually stars, planets, living beings and atoms will all get torn apart unless something counters the accelerating expansion. See my reply to ajross. Dark energy is not the same as a "Big Rip" scenario, which is what you are describing.
- Santosh83 9y ago
  Thanks for the correction.

pavel_lishin 9y ago

As far as I know, the Sun will be long gone by the time that level of expansion is reached; at best, it'll be a tiny white dwarf, having long ceased its expansion. It can really be described as a problem that doesn't concern humanity, because by the time it hits, we won't be recognizably human anymore :P

pdonis 9y ago

> I didn't realize that the expansion of the universe was overcoming gravity within the scope of a galaxy. It isn't, at least not according to our best current models, which do not involve a "Big Rip" scenario. See my replies to others downthread. > Does this also mean that the distance between planets within a solar system will increase? Does this mean that the distance from the Earth to the moon is increasing, and does it mean the planet itself is expanding? Is the expansion of the universe a destabilizing effect on orbital mechanics? According to our best current models (i.e., in the absence of a "Big Rip"), no to all of these.