Does the universe need an escape velocity?

[jhe1984]

The question is, Does the universe (the conglomeration of all energy in existence) logically require an escape velocity?

My reasoning is thus. If the universe is at least partially composed of massive objects that exert gravitational pull, wouldn't the sum of every massive object in the universe and it's corresponding gravity factor into some finite (although perhaps unknowable) force from which we could calculate a theoretical escape velocity - what we'd escape into, I'm not sure :eek: ?

If the answer turns out to be beyond the speed of light, wouldn't that mean that we are in some type of a black hole?

This hardly seems logical but I can't locate the break.

Thanks.

[chroot]

It's an interesting question. Keep in mind that the notion of an "escape velocity" necessarily involves some gravity well with finite extent. You start out with some minimum gravitational potential energy, and continue to gain gravitational potential energy forever. It implies that you can move away from the object from which you are escaping.

On the other hand, the universe's geometry is "closed" in the sense that you cannot leave it, no matter if it's finite or infinite in extent. Also, one of our tacit assumptions is that the universe is homogenous at large scales -- that is, the matter density is roughly the same in every reasonably large volume of space.

This means that, while you can move away from one galaxy and "escape" it, you're necessarily moving toward some other galaxy, and will end up bound to it. There's no way to get away from ALL the matter in the universe at the same time, because the matter density is believed to be constant throughout its entire extent.

- Warren

[jhe1984]

Okay but, all that being said, wouldn't there at least be some sort of rim to this gravitational well (even if we could never reach it), which, provided we knew the mass of everything in the universe, would be calculable?

A similar question would be, if for whatever reason 1/3 of all the mass in the universe was simultaneously converted entirely into energy, wouldn't this produce some sort of gravitational wave or waves?

If so, where would this gravitational wave expand into?

:bugeye:

[chroot]

No, the universe does not have a 'rim.' If it's finite in bound and curved, like the surface of an apple, there's no place you can go to be "away" from the rest of the matter in the universe.

If the universe is infinite, and homogenous everywhere, you still cannot go anywhere to get "away" from the matter.

- Warren

[jhe1984]

...And that's the stumper.

Isn't there necessarily a fundamental disconnect somewhere then, between our understanding of local gravity, which is intrinsically connected to finite distances, and the universe's macro-gravity behavior?

The closest conceptualization I can think of is the inside of a black hole. Hmm.

[Chronos]

It does not 'matter' if matter is converted to energy. Energy exerts the same gravitational influence on the universe as does its matter equivalent. It would have a local effect [e.g., if the sun converted a significant portion of its mass to energy, planetary orbits would change], but it would not make any difference on cosmological scales.

[jhe1984]

"Energy exerts the same gravitational influence on the universe as does its matter equivalent"

Cool, I've been wondering about this. I guess this means that an individual photon has gravitational influence (albeit small). Okay but bear with me hear: this means that the total gravitational force of the entire universe since the Big Bang has not changed (except locally), it's just converted from mass to light and vice versa?

One last, seemingly unrelated, question - is the force or amount of dark energy changing or has it changed OR has it kept the same ratio (as we factor now) since the BB?

Sorry, sometimes I feel like I'm spamming this site with questions. :confused:

[Vern H. Ranney]

Only a theory because I haven't been able to exact a value to the mass and velocity of all particals durring the first few moments post big bang, but, escape velocity from falling back into singularity may have been achieved by "the draw of the nothing on the something." Do you remember the jr high experiment with a single drop of oil in a vacume, the mass tends to expand to fill the space available.