What Does Gravity Have To Do WithThe Expanding Universe?

[Anomalocaris]

Why do you think that's a rule?

Interesting question.

In fact, the universe is the ONLY thing that's expending. Electrons aren't moving away from their respective nucleons. planets aren't moving away from their respective suns. Stars within a galaxy aren't moving away from each other. Only galaxies are moving away from one another,      e r go, the raisin bread dough model.

so, yes, it's possible for dark energy to be the only thing that has no counter, not as a rule, but just the way things are.

In time we may move so far from other galaxies that we think we're the only one. Or we may move into the viciiity of another universe and not realize it's another. How will astrologers explain the weird constellations?

I don’t believe what you say is quite true.   Expansion of the universe and the impact of the Dark energy of the universe affect all things, including stars in galaxies and electrons in atoms.  Right now at the distance scale seen between stars in a galaxy, or anything smaller, the strength of gravity or other fundamental forced overwhelms the pressure of dark energy.  So ignoring the pressure of dark energy and it’s effects on the expansion of space between stars gives an accurate enough approximation.

As to what astrologers will think when expansion of the universe moves all other galaxy beyond our observation horizon, well. First of all, all the constellation are made up of stars inside Milky Way, and indeed all but a very small handful of objects visible to the naked eye are Located in parts of the Milky Way very close to us, say 3000 light years inside a galaxy 100,000 lightyears across. So moving other galaxies beyond our observation horizon will have little noticeable impact on the sky visible to naked eye astrologers.


But. In the amount of time it would take for expansion of the universe to move all other galaxies beyond our visible horizon, all the stars in the currently in the Milky Way, and all the stars that would ever form normally from material available would have long since expended all their fuels, died, and their corpses cooled until their surface temperatures are close to the cosmic background. The same would apply to all other galaxies.

So. By the time all other galaxies recedes from our visible horizon, carried by the expansion of the universe, our galaxy would be almost totally dark, with no luminous stars. There would only be some extremely faint radio wavelength glows from cooling star cinders and Hawkins radiation from black holes, punctuated at extremely long intervals by brilliant flashes signifying collisions between stellar corpses, or hawkin evaporation of blackholes. No biological eye known to us would be sensitive enough to pick up the faint stead glow from the dead galaxy as we would have by then, much less see constellations.

[vulcanlogician]

Astrologers? You didn't eat your Wheaties this morning, did you, Anom?

[Haipule]

But, can't ferromagnetism, paramagnetism, diamagnetism, centripetal force and inertia explain everything that gravity appears to be?

[LastPoet]

I've read some (I suppose they were) scientists argue that there’s not enough gravity to reverse inflation and cause                the universe to collapse back to where it was before the Big Bang.

Gravity affects matter, but according to ye ol’ raisin bread dough theory it’s not matter but space that’s expanding. Why would scientists use the properties of matter and gravity to understand something that has nothing to do with either?

If we understand the properties of “space” and what’s causing it to expand, we will be able to predict whether it will one day (or eon) collapse.

I miss alex k...

[polymath257]

But, can't ferromagnetism, paramagnetism, diamagnetism, centripetal force and inertia explain everything that gravity appears to be?

No. Electromagnetism is *way* stronger than gravity. Partly because of that, matter tends to be both magnetically and electrically neutral.

One way to see this: if you have a small magnet, it can produce sufficient force to counteract the gravity of the whole earth.

Gravity is a different thing than magnetism by orders of magnitude.

[vulcanlogician]

Gravity is a curvature of spacetime. 

Why do some physicists think that there may be a "graviton" particle through which gravity operates? If gravity is explained as a curvature of spacetime, what function would a particle have? Just curious.

[Haipule]

But, can't ferromagnetism, paramagnetism, diamagnetism, centripetal force and inertia explain everything that gravity appears to be?

No. Electromagnetism is *way* stronger than gravity. Partly because of that, matter tends to be both magnetically and electrically neutral.

One way to see this: if you have a small magnet, it can produce sufficient force to counteract the gravity of the whole earth.

Gravity is a different thing than magnetism by orders of magnitude.

Can I use phonons to effect magnetism? This is difficult to study because of magnets in speakers. Any help would be appreciated. And should it be ultra(VHF, UHF) or infrasonic? I'm in way over my head!

[The Grand Nudger]

The idea is that curvature is the classical limit, and a graviton could offer deeper insight to it, within qft. IIRC. Break out the whips, we need to start flogging some physicists.

[Rhondazvous]

One way to look at dark energy is as the 'energy of empty space'. So, when space expands, there is more space, and hence more dark energy.

This extra energy has to be balanced, yes, but it is balanced by a decrease in the curvature of spacetime, which accelerates the expansion of space.

For ordinary matter and dark matter, when space expands, the total amounts of matter stay the same, but it is spread out more. This serves to gradually slow expansion.

For radiation (like light), expansion actually decreases the total amount of energy, which slows the expansion more.

So, in the very early universe, which was radiation dominated, the expansion was slowing, decelerating fairly fast. Later, when matter dominated, the expansion was still slowing, but not as fast. Now, with dark energy dominating, the expansion has started to accelerate. it's all a play-off between the different components of the universe and how the respond to expansion. And that is all about gravity.

Was spacetime ever curved? Light (photons, energy) curves when it comes within the vicinity of a body of matter. But in the beginning there was no matter, ergo, no gravity until recombination. Wouldn't that make spacetime/energy that isn't within the vicinity of a body of matter linear rather than curved and that would also account for acceleration.

The universe doesn't orbit around a center like matter does. It just moves outward

[Anomalocaris]

Was spacetime ever curved? Light (photons, energy) curves when it comes within the vicinity of a body of matter. But in the beginning there was no matter, ergo, no gravity until  recombination.  Wouldn't that make spacetime/energy that isn't within the vicinity of a body of matter linear rather than curved and that would also account for acceleration.

The universe doesn't orbit around a center like matter does. It just moves outward

I think the highlighted part is not accurate for two reasons:

1.  Matter with rest mass in the form of electrons and protons existed before recombination.  Recombination simply allows electron and protons to combined to form electrically neutral matter that is transparent to light.  Recombination was the first moment in the history of the universe when photons could propagate through space without being absorbed by charged particles.   So it is the earliest moment that we can look back in time by looking out through 13 billion light years to actually see matter.  Prior to that space itself was filled with ionized matter but was opaque, so we’ll see nothing if we try to use photons to see back further.  But matter definitely existed before that time.

2.  Even before electrons and protons themselves first formed,  the energy that will eventually become electrons and positrons had already existed since the Big Bang itself.  Energy by E=MC^2 is equivalent to mass and for that reason excerpts its own gravity.   Photons, for example, possesses its own gravity.  The gravity is very small because by E=MC^2, even the energy of the most energetic photons is equivalent to only an infinitesimal amount of mass.   But Wherever there is net positive energy, regardless of whether the Nagy is in the form of matter with rest mass, or particle without test mass, there is essence of what curves space time and hence there is granvity.  Matter strictly in the forms colloquially called matter is not required.   The curvature of the entire universe was affected (but not necessarily dominated) by gravity the moment it was created in the Big Bang.

Also, Since universe is open, this means space is hyperbolically curved on a cosmological scale by an amount greater than collective gravity of all mass and energy in the universe can cancel out.   So curvature of space time does not just occur locally under local gravity in the vicinity of great masses.

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Astrologers? You didn't eat your Wheaties this morning, did you, Anom?

I have total confidence in the ability of ignorance and superstition to outlast everything else and still be there at the heat death of the universe.