What is the escape velocity of the Universe?

Question

All objects with gravity have an escape velocity where an object traveling at a certain speed can not be captured by the object. For Earth it is 7 miles per second, for an asteroid you can jump fast enough to achieve it.

If you consinder all the mass in the known Universe, what is the escape velocity?

Answer 1

There are many perspectives to this question. Strictly speacking, you can not leave the universe as currently undertood. Meaning that it is believed that the universe is a closed in four dimensions and finite in three. Think of a balloon from a two dimensional perspective. A balloon has a two dimensional surface but occupies three dimensions. You could not leave it's surface and it has finite surface area but would appear infinite since you could travel forever inany direction within the available two dimensions. Likewise you could travel forever in any direction of space, you could never leave it or reach an "end" and yet it is of finite volume.
The next best perspective has to do with cosmology. That is, does the universe continue to expand (like blowing up the balloon) or does it eventually slow, stop and then begin to contract under gravitational forces. This has not been answered yet. The question is, is the momentum of the expanding universe sufficient to overcome the gravitation of the mass of the universe - very similar to your question. The answer is not yet known to any dgree of certainty because we don't know if we can account for all of the matter/energy in the universe. Things like dark matter/energy and black holes make it difficult to ascertain. There are "guestamates" but not of sufficient certainty to have a good idea of which is the ultimate fate of the universe.
This makes the answer to the hypothetical question of the escape velocity of the universe, where it hypothetically analogous to the escape of a planet or solar system, difficult. I suppose one could take best guess as to the mass of the universe and plug it into the math one would use to determine the escape velocity of the solar system.

Answer 2

Socialdeevolution, you can't say for a fact that the universe isn't infinite, only that the "visible universe" isn't. The visible portion may only be a local expanding region in something entirely larger. And matter doesn't have to occupy every point of space in order for it to be infinite... if space were infinite, even if there were only 1 atom of matter per cubic lightyear, it would still be impossible to give a number that defines the quantity of matter. So if a person assumes that space is infinite, it would make sense to say that matter is as well, as long as the average desity is greater than 0. (That said, I don't necessarily think either space or matter is infinite, but the position is plausible.)

As for the gravitational arguments that one could escape from the universe as "easily" as escaping from the solar system (a "dog paddle" has been mentioned), I suggest that it is not nearly as easy as you think. After all, the planets, meteors, and comets are all moving at very high speeds, yet do not in most cases escape solar orbit. And if they do, they still swirl about the Milky Way in more or less the same path as our solar system. And if the hypothetical situation of escaping the universe were possible, you'd end up at an "edge" of sorts, at which most of the mass of the universe is behind you, and very little in front, thus making an escape highly difficult.

And the situation on the whole is pretty much impossible, for all the reasons outlined in Dr Spock's fantastic answer, above.

Answer 3

I doubt anyone can (theoretically) answer this with any accuracy since the mass of the universe isn't known to an exact figure, but I'd imagine the escape velocity (if escape were possible) would actually be much lower than people seem to think.

Imagine trying to leave our solar system. Sure, there's the mass of the sun, the planets and all that other junk in our solar system, but their gravitational pull is very small and easy to overcome unless you're close to a particular object. You could literally paddle out of our solar system with your arms and legs. It would likely be the same with the universe. Unless you were 'blasting off' from the surface of something with a large mass, escape wouldn't be difficult. However, I don't know if the physics would be quite the same when you're leaving the universe, which isn't actually possible.

And to socialdeevolution: An infinite amount of matter doesn't require the universe to be completely full of matter for it to be infinite. There could only be one speck of dust for every 100,000 square km's of a universe, but as long as that universe is infinite, there will be an infinite number of specks of dust, and therefore infinite matter. Not that I'm saying our universe is infinite; it isn't.

Answer 4

The escape velocity from the surface of a rotating body depends on direction in which the escaping body travels. For example, as the Earth's rotational velocity is 465 m/s to the east at the equator, a rocket launched tangentially from the Earth's equator to the east requires an initial velocity of about 10.735 km/s relative to earth to escape whereas a rocket launched tangentially from the Earth's equator to the west requires an initial velocity of about 11.665 km/s relative to earth

Answer 5

Well.. I could be wrong, but I'm thinking that the universe isn't a mass of matter with gravity. It contains a lot of masses, and these masses have gravity, but the universe itself is different. I don't think it's possible to get out of the universe, not because of gravity but because, well, there's nothing there. Course, I don't think anyone knows for sure.

Answer 6

Hi. An infinite universe tends to mean an infinite mass and therefore an infinite escape velocity, or as close to that speed as possible. I think even 'c' is not fast enough.

Answer 7

well we know that the gravational field of any object of mass decreases as the distance between you and that object increases. so given that your are not located anywhere close to a large amount of matter, i.e. star or nuetron star, then you should be able to move freely about the vacumm of space. therefore, if there is an edge to the universe, the amount of veloctiy needed to escape would be close to zero.

Answer 8

The Universe doesn't have an "escape velocity" that can somehow be tied as in the usual Newtonian calculation of that quantity, to one specific mass M and one specific leaving point at distance R from the centre of that mass. It simply just doesn't work that way.

Yet all is not lost. There are two other answers one could give to the question. (Both kinds of answer are necesssarily idealized because the actual Universe is too messy to use as an example). See how you like them:

1. Consider a flat Universe that is large enough overall, in which Hubble's relationship V = Ho D holds for everyone, with the Hubble "constant" Ho REALLY constant. (In our Universe, though it's remarkably FLAT according to recent results, H isn't Ho, a constant. It actually changes with time from the Big Bang. But ignore that, for illustrative purposes.)

The fact that "space is expanding" means that for each 100 Mpc (or whatever) that we go out into the Universe, a definite amount of "extra distance" is being added, per second. If you go out far enough, then, the total "extra distance" being added out to there per second exceeds 3 x 10^10 cms, or 3 x 10^8 m. But those distances added, PER SECOND, means that light can't catch up to any part of the Universe beyond there!

That means that light rays starting from here can never go out more than a finite distance --- even though there's more Universe out there beyond that distance. (MInd blowing.) There's an "information horizon" (as far as we're concerned), for our information getting to and beyond that distance.

But that means that the Universe out to that distance from us satisfies the definition of a Black Hole, from our point of view! (Our) light can't "escape" from this particular part of the Universe surrounding us. So, out at that distance, it's AS THOUGH the "escape velocity" had reached the speed of light.

(Don't take this analogy too far and say: "Oh, but that means the "speeds" of galaxies are even greater than that of light out there. But that's not allowed by Special Relativity; so there must be some mistake in the logic." That's a false conclusion. The inter-comparison of speeds is actually a fairly local transaction. In General Relativity, which you really have to use in the context of the Universe, to compare two things far apart you actually have to know how to "transport" one of them to the other place, to do the comparison. The rules for that aren't obvious. Etc., etc., etc.

While NOTHING can ever exceed the speed of light LOCALLY, there's nothing that says that an expanding space can't "add" more distance between two very separated objects than light could cover locally in that same time. Mind-blowing? --- You bet! But it's fitting --- both the Universe AND our minds are being stretched, in its very contemplation.)

2. Back to the simple Hubble Relationship, V = Ho D, once again.

We've recently learned through the 'WMAP' satellite that the Universe seems to be EXTREMELY close to FLAT, with lots of mysterious stuff making up for a prevously HUGE discrepancy between what we could see out there and the so-callled 'closure density.' (This might seem like wishful thinking, but supposedly sober cosmologists are telling us this, and there's little doubt that the Nobel Foundation will buy it at some stage.)

Then, in rather a trite sense, the Hubble relationship is effectively telling us that the coupled values of ''V' and 'D' at any distance are giving the escape velocity 'V' (from us) of cosmic stuff out at that distance, 'D' !

So the Answer to the BIG Question, "What is the escape velocity of the Universe?" is:

Whatever you want it to be!

(Give me a speed, 'V,' and I can tell you just how far out to go so that Universal expansion will carry you away from me for ever.)

With little twists like 'dark energy,' that answer would be changed somewhat. Nevertheless, I hope I've given you a glimpse of why the answer simply can't be as definite as in the simplest Newtonian context.

Answer 9

you would have to be able to orbit around the universe for this scenario to be possible. i dont think that the universe has enough gravity to sustain orbit at its current size.

i guess you could also look at it as C because if you move faster than C you would then have kind of switched times. and if you look at time travel as moving into another universe, you would have escaped your universe and gone into one in the past.

Answer 10

Warp 10