What if Kerbin exists?

[mincespy]

If the universe was infinite, there would be infinite gravitational pull everywhere. There isn\'t.

[Endeavour]

If the universe was infinite, there would be infinite gravitational pull everywhere. There isn\'t.

The amount of matter in the universe is not infinite, just space.

[CaptainArbitrary]

If the universe was infinite, there would be infinite gravitational pull everywhere. There isn\'t.

That\'s not how gravity works. Gravitational acceleration is a function of the curvature tensor, which is a function of the stress-energy tensor. Put simply, how much gravitational acceleration an observer measures at a given point in space depends on energy and momentum density and flux, not just on the total energy.

[mincespy]

The Universe is not infinite. It is however, expanding all the time, and insanely fast. There is no way it could have expanded to be infinite, because then that just about invalidates the big bang theory.

[Jaydee]

The Universe is not infinite. It is however, expanding all the time, and insanely fast. There is no way it could have expanded to be infinite, because then that just about invalidates the big bang theory.

Maybe the 'space' is infinite, but the universe isn\'t ?

[Candre]

It is theorized that super-dense trans-uranium elements can exist, which have extremely long half-lifes.

Island of Stability

Also, we\'re not really in a position to judge whether the universe is infinite. They say we\'ve measured it, but these are only predictions based on what is visible and the extrapolation of the origin of the universe. What about the possibility of a multiverse? We could always have infinite universes. Not seeing them doesn\'t make it impossible.

Also, if we assume that the universe is infinite, gravity wouldn\'t be infinite. Gravity also abides by relativity, which means that it takes time for a gravitational field to reach something at a distance. Considering that we can barely see 13 billion years ago into our own universe, universes outside would not be able to exert any force on our universe. Even if you posit that all mass existed forever, and that gravitational waves managed to spread across the entire universe, we would still, according to the Shell theorem, feel absolutely no force. Remember, there is infinite mass in every direction, so therefore a force in every direction. That cancels itself out. Even then, although I\'m too lazy to work it out, the sum of infinite numbers that get smaller and smaller equates to a finite value. Think:

which evaluates to 2.

Please point out any mistakes.

I love the idea that Kerbals exist somewhere in the universe. I wouldn\'t go near them, though.

[CaptainArbitrary]

The Universe is not infinite. It is however, expanding all the time, and insanely fast. There is no way it could have expanded to be infinite, because then that just about invalidates the big bang theory.

Nope. The universe was always infinite. The thing that\'s expanding is the scale factor which determines distances between fixed points.

And it\'s hardly 'insanely fast.' At present it\'s a mere 70 kilometers per second per megaparsec. That\'s incredibly tiny.

[Jaydee]

Nope. The universe was always infinite. The thing that\'s expanding is the scale factor which determines distances between fixed points.

And it\'s hardly 'insanely fast.' At present it\'s a mere 70 kilometers per second per megaparsec. That\'s incredibly tiny.

Yep, I said space though, I think the universe is the distance we can observe ( observable universe ). Space is the amount which it can expand into, which is infinite.

[CaptainArbitrary]

Yep, I said space though, I think the universe is the distance we can observe ( observable universe ). Space is the amount which it can expand into, which is infinite.

Okay, but now you\'re just playing word games. I could define 'universe' to mean the inside of my house, then say the universe is just 2000 square feet.

We already have a word for what you\'re saying. In fact you used it. It\'s observable.

[mincespy]

Nope. The universe was always infinite. The thing that\'s expanding is the scale factor which determines distances between fixed points.

And it\'s hardly 'insanely fast.' At present it\'s a mere 70 kilometers per second per megaparsec. That\'s incredibly tiny.

How did it begin, though? Everything must have a beginning. And if it was always infinite, wouldn\'t there be infinite entropy, which there isn\'t? Granted, there is a lot of entropy, but not an infinite amount.

[ForumHelper]

Considering how big the universe is, they might exist. In fact, a lot of stuff can exist somewhere(Spaceship troopers anyone?)

[rdfox]

For the record, the current theory is that the universe *is* infinite, and that in the first few milliseconds after the Big Bang, it grew to its current infinite state in what is called the 'Great Expansion,' during the period when the energy levels were still so high that the laws of physics were still as unsettled as frat boys on a Friday night; once the initial energy had dissipated enough that physics stopped screwing around and settled on a speed of light, things got so that we could actually figure out what the hell was going on. The first second or so is basically terra incognita, and always will be, since it took that long for the basic laws of physics to work out what they would be and what certain key physical constants (speed of light in a vacuum, the gravitational constant, and the laws of thermodynamics among them) would be for this universe.

What\'s more, it\'s not just that all objects are traveling radially outward from the center like you\'d expect from an explosion--if that was the case, then you\'d expect there to be speed variations determined by the mass of the objects, not by the object\'s distance from Earth, and by the direction relative to the burst point, with objects along our vector of movement having less apparent speed than objects off-axis to us. However, what we\'ve determined is that:

A) On a scale larger than our gravitationally-bound Local Group of Galaxies, all objects in the observable universe are *receding* from us. At smaller scales, this isn\'t true, as the gravitationally-bound clusters of matter (from planetary systems to local groups) can have different motions within them (obviously, since Earth orbits Sol, and the Andromeda Galaxy will collide with our own Milky Way in about five billion years), but overall, every object in the universe is getting further away from us.

The speed with which an object is moving away from us is related directly to its distance from us--the further away it is, the faster it\'s receding.

There\'s only one real way to reconcile these two facts, and it\'s pretty mind-blowing if you think about it. Since we work on the basic assumption that there is Nothing Special about Earth (i.e., we\'re just some random planet orbiting some random star in some random galaxy in some random local group), we know that we are *not* at the center point of a universe-creating explosion. Instead, space itself is getting larger. If you think of it as a sheet of graph paper, the only way that you can make it so that every point on the graph constantly gets further away from every other point, and the speed at which they do increases with the distance between any pair of points, is to assume that the points are fixed coordinates relative to the graph paper (i.e., the point at (1,3) will always be on the intersection of the first line right of the origin and the third line above the origin), but the paper itself is growing, so the lines are getting further apart. So the universe isn\'t just infinite, but it\'s also still growing, just not as fast as it was in the first second of existence.

Oh, and if you want your mind blown a little more? There\'s one more thing we recently determined that completely blew the cosmologists\' minds:

C) The rate at which the universe is expanding is not decreasing, as one would expect due to gravity. (Even if you assume that it\'s an 'open' universe in which all objects are moving at or above escape velocity relative to all other objects, they would still be slowing down due to gravity.) In fact--and here\'s the part that flabbergasted the Hawkings and Kakus of the world--it\'s actually INCREASING. This implies that in addition to the not-currently-detectable 'dark matter' that has been determined to make up most of the mass of the universe, there is a very mysterious and not-yet-detectable 'dark energy' that\'s pushing the expansion of the universe harder than the effect of gravity trying to pull it back together.

More and more, reality is turning out to be like Rowdy Roddy Piper always said he was--'Just when you think you\'ve got the answers, I change the questions!' ;P

[TelluriumCrystal]

And thats not even mentioning Brane theory! 8)

From what I can make of it, Brane theory suggests that our universe exists in a multiverse of unknown size (assumed to be infinite) with an unknown number of (again, assumed infinite) universes in it. These universes actually move around and can influence each other. One proposed solution for the question of why gravity is so weak is that it is in fact an influence from another universe. The big bang is theorized to have been caused by a collision between our universe and another, effectively hitting the \'reset button\' on ours due to the insane amounts of energy released in the collision... Also, each universe has its own laws of physics (or none at all...) and due to their infinite nature, I\'m sure Kerbin exists in one of them somewhere!

Also, I am no expert on this stuff and apparently Brane theory isn\'t very widely accepted, so don\'t take my word for it. Use google!

[Steve5451]

That means that there are kerbals somewhere asking 'What if Earth exists?' on the 'Human Space Program' forums.

[Accelerando]

And thats not even mentioning Brain theory! 8)

From what I can make of it, Brain theory suggests that our universe exists in a multiverse of unknown size (assumed to be infinite) with an unknown number of (again, assumed infinite) universes in it. These universes actually move around and can influence each other. One proposed solution for the question of why gravity is so weak is that it is in fact an influence from another universe. The big bang is theorized to have been caused by a collision between our universe and another, effectively hitting the \'reset button\' on ours due to the insane amounts of energy released in the collision... Also, each universe has its own laws of physics (or none at all...) and due to their infinite nature, I\'m sure Kerbin exists in one of them somewhere!

Also, I am no expert on this stuff and apparently Brain theory isn\'t very widely accepted, so don\'t take my word for it. Use google!

I believe you\'re talking about 'Brane' theory, as in membrane, not the human brain. The version of brane theory I am familiar with posits mostly what you say, but rather than gravity being weak due to its being an outside force, gravity\'s weakness is theorized to be due to the fact that it leaks out between branes — i.e., that things in our universe are capable of exerting gravitational force by way of gravitons, but that those gravitons tend to leak through the 'membrane' of our universe and into other universes. Incidentally, this also means that gravity would be the most effective tool for communication between our universe and others, if humans could understand how to use it in this way.

On another note, how would universes or branes with different laws of physics (or none at all) coexist with ours in the multiverse? How would each reality square with the other?

[TelluriumCrystal]

On another note, how would universes or branes with different laws of physics (or none at all) coexist with ours in the multiverse? How would each reality square with the other?

I have no idea... Perhaps there are a few 'multiverse-wide' laws that keep reality from flickering out. That way everything can coexist. Either that or the 'space' in-between universes has its own laws.

Also fixed the spelling of Brane in my earlier post... =P

[CaptainArbitrary]

To say that brane cosmology is not widely accepted is putting it too lightly. As serious science goes, brane cosmology is right up there with the 'turtles all the way down' thing.

You can\'t even sensibly call it a theory. It\'s just a mathematical model. One which, it bears mentioning, is so far completely contradicted by reality.

Basically no one serious gives any credence at all to the idea of 'multiple universes.' It\'s not even a meaningful turn of phrase. The only places that idea ever comes up are bad science fiction and worse science journalism.

[TelluriumCrystal]

To say that brane cosmology is not widely accepted is putting it too lightly. As serious science goes, brane cosmology is right up there with the 'turtles all the way down' thing.

You can\'t even sensibly call it a theory. It\'s just a mathematical model. One which, it bears mentioning, is so far completely contradicted by reality.

Basically no one serious gives any credence at all to the idea of 'multiple universes.' It\'s not even a meaningful turn of phrase. The only places that idea ever comes up are bad science fiction and worse science journalism.

Isn\'t that pretty much how the Big Bang theory started out? As a revolutionary idea that nobody can quite believe is possible and that mainstream science disagrees with? Sure, it may just be another random theory that will never amount to anything, but I can\'t help but get the feeling that its on to something.

Also, please don\'t say it isn\'t a theory, given that the definition of a theory is \'A supposition or a system of ideas intended to explain something\'. How accepted it is in the scientific community does not change this.

Anyways lets get the topic back on track:

I wonder if the kerbals use a patched-conics system, and have never considered the possibility of a more complex way of measuring orbits...

[CaptainArbitrary]

Isn\'t that pretty much how the Big Bang theory started out?

No, it is not. Lemaitre\'s ideas were both sensible and consistent with the facts, so they were accepted as plausible basically the moment they were published. (By everybody except Hoyle, but he gave us a great name, so all is forgiven.)

Sure, it may just be another random theory that will never amount to anything, but I can\'t help but get the feeling that its on to something.

That\'s really not how science works, I\'m afraid.

Also, please don\'t say it isn\'t a theory, given that the definition of a theory is \'A supposition or a system of ideas intended to explain something\'. How accepted it is in the scientific community does not change this.

That isn\'t the definition of a theory, in this context. That\'s the colloquial definition, which is synonymous with a guess. In science, a theory is a rigorous and internally consistent set of ideas which both are consistent with existing observations and correctly predictive of as-yet-unmade observations. Brane cosmology is none of those things. That\'s why I said what I said: Too many people think 'theory' just means 'any old thing anybody makes up.' That\'s really not what science is. Science works specifically because that\'s not what a theory is.

[popeter123]

if it went by rp kerbin would be nuked to nothing