The universe and infinity.

[Poisoner]

I was thinking earlier of why the universe couldn't of just existed without a beginning or end and then I thought of a geometry analogy that I thought put it into perspective. If the universe was truly infinite, it would be like a line. If it had a beginning and an end, then it would be a line segment. If it had a beginning with no end, the universe would become a ray.

So, doesn't the idea of a beginning and an end destroy any chance of the universe being infinite?

Also, this raises the question of what infinities would the universe require to be "infinite".

[Boyar Son]

NASA says the universe can contract too, depending "on the density and pressure of matter" in the universe. so the universe could expand forever i guess. depending on momentum of expansion or pull of gravity (gravity contracting the universe). either way it can go.

[Elfdude]

It's a property of dimensions. In 2 dimensions infinite is much smaller in scope than in 3 dimensions because the limitations in 2 dimensions mean every 2 dimensional possibility can be exhausted much faster than in 3 dimensions. Similarly the universe is not only 3 dimensional. So if you apply the 4th dimension (popularly dubbed spacetime) suddenly infinity includes past present and future and every spatial anomaly in between. If you include the 5th dimension infinity includes all possible timelines for our universe not just the finite pathway of the 4th dimension. If you include the 6th dimension infinity includes all possible timelines and all possible crisscrosses of those timelines.

The problem with your perception is that we're 3 dimensional beings. Even though the other dimensions have affects upon us we cannot perceive time and space in any other way than the symptoms it produces upon our limited 3 dimensional perception. Thus the universe up to the 12 established dimensions, which may grow if we discover even larger dimensions or shrink if the mathematics or physics needs to be clarified, is effectively infinite. Our inability to perceive the other dimensions makes the concept of infinity difficult for many to accept. The question isn't whether our universe is infinite or not but what, if anything, makes something impossible.

[MaryPoppinCaps]

If the universe expands and contracts, what is the space considered around it that it moves in and out of?

[Elfdude]

If the universe expands and contracts, what is the space considered around it that it moves in and out of?

It would be misinformed to consider the area outside of a universe space. Space time inside our universe is infinite not because it stretches some hypothetical bubble outwards that would imply there's some force that reverses this expansion. No the space within a universe is infinite. You're committing the same perceptual mistake as a hypothetical flat lander on a mobius strip. Before you can leave this universe and travel to another one you would need to master dimensional travel on a level that makes time travel, teleportation and wormholes look like savagery.

[Tacitursa]

Ive always wondered if the universe has an edge like were in some kind of bubble.

[MaryPoppinCaps]

It would be misinformed to consider the area outside of a universe space. Space time inside our universe is infinite not because it stretches some hypothetical bubble outwards that would imply there's some force that reverses this expansion. No the space within a universe is infinite. You're committing the same perceptual mistake as a hypothetical flat lander on a mobius strip. Before you can leave this universe and travel to another one you would need to master dimensional travel on a level that makes time travel, teleportation and wormholes look like savagery.

And how do [can] you know this for sure?

[Boyar Son]

imply there's some force that reverses this expansion.

Sure?

Gravity does not contract the expansion of the universe?

[Arch-hereticK]

The universe is finite but is infinitely expanding, space has to be defined, but it's capacity is infinite (theoretically).

[Amorphos]

So, doesn't the idea of a beginning and an end destroy any chance of the universe being infinite?

The universe could be like a bead on a string [roughly speaking] and the string could be infinite.

What we need to do is describe reality and then the universe within that, not the other way around. if you dont describe reality as infinite then it tends to leave rather huge gaps. for example if you have an objective infinite at either end of the universe, then the universe cannot exist as there is no objective space left for it. so we have to describe a universality that includes both.

[pericles_plato]

To infinity and beyond!

[Lupu]

The universe is as big as it needs to be, because you are part of the universe, you can't get out of the universe. Travel beyond anything, and you have only made the universe bigger. If there isn't a border somewhere, I believe the universe is infinite because, while it is not of infinite size, it is everything, so anything outside everything is still part of everything, so the universe is a big as it needs to be, no more, no less.

[MaryPoppinCaps]

Indeed. Seems like some areas of science are mostly theories and speculation.

[Elfdude]

And how do [can] you know this for sure?

You can never know something for 100% sure until omniscience is reached. Since we're pretty far away from omniscience we're pretty far from knowing absolutely anything for sure. In human reality truth is effectively a very high probability. When calculating probability science relies upon Occam's razor to separate claims with low probability which have a high amount of assumptions or large scope of assumption that are dependent (inductive reasoning) upon each other from claims of high probability which have large amounts of evidence, few assumptions (deductive reasoning), assumptions don't matter with respect to the information within the theory.

The gradient from purely inductive reasoning to deductive reasoning corresponds to the probability of the theory being right in comparison to other theories. It's entirely luck if a theory with a lower probability turns out to be true(r) but science doesn't base it's claims off of luck. Science doesn't base it's claims off of luck because for example, if we believe fairies make our milk go bad we have a suitable reasonable claim (inductively) but because of the high amount of assumptions we must make (bacteria in the milk don't do anything, fairies get in our fridge, we never see fairies etc) to create that opinion it's just as likely to be true as unicorns. Further we can't do anything with the assumption except assume more things go bad because of fairies nor does it explain why if we sterilize the milk it doesn't go bad. Science instead asserts germ theory is the best explanation of why milk goes bad because germs are present, germs produce toxins, these toxins make milk taste sour, thus germs must cause milk to go sour.

There is evidence for what is outside of the universe but you'll really have to delve into quantum mechanics and what not for more information. Bubble theory, inflation theory, string theory are great places to start and will give you a pretty good overview of the evidence provided for what is outside of our universe why our universe is infinite etc etc.

Sure?

Gravity does not contract the expansion of the universe?

Gravity does not act as a boundary. Between any two points anywhere in the universe there is a gravitational attraction. Early on gravity had a much greater affect on the universe's size but expansion has been speeding up ever since the initial laws of the universe crystallized.

Indeed. Seems like some areas of science are mostly theories and speculation.

This is false. Speculation is merely the first step of the scientific method, to compare it to a theory is like comparing a star to a fire. A scientific theory is any idea in which the assumption made within is moot in regards to how reality works. Thus the theory of gravity is a theory because we don't know where gravity comes from, why or how it's so weak in comparison to the other forces. However if we discover tomorrow that what we've been calling gravity is actually an entirely different force it doesn't change the useful information within the theory. This is why we still use newton's ideas for basic calculations regarding gravity despite the fact they've been supplanted with a more accurate theory.

[vlach]

Well the problem isn't very straightforward, really we require the universe to be infinite. We can define the edge of the universe as a place where the forces al go to zero since we know any point in the universe relative to another by say the gravitational pull it feels if it felt no force whatsoever it can be said to be undefined space and indeed it would be an undefined particle it would not have speed, mass etc since these are all relative to something else. Now we have two long range forces electromagnetic and gravity which both have a dependence of 1/distance squared and the only place both of these are zero is at infinity thus the universe is infinite. There is nothing philosophical about the infinite nature of the universe it comes out of the laws the constituents of the universe obey the only conditions imposed on the existence of the universe is that it contain more than one separate entity. One can say that beyond a certain point there is no more matter however the reach of that matter is infinite and therefore other matter can exist beyond that point making it itself a part of the universe, consequently the space in which matter can exist i.e the universe is infinite.

Although science is not pure speculation the mathematics currently used to describe interactions of matter on the subatomic scale has led us to some undesirable results (like the infinite energy of empty space and nonsensical behaviour of particles) that have forced us to hammer in terms just to cancel the undesired ones; essentially we're forcing the mathematics to do what we want without any justification from first principles. This has led to the creation of unintuitive but mathematically desirable ideas such as supper-symmetry (something for which experimental evidence is still lacking) to try and justify all of these artificial corrections. As well as string theory which itself has problems leading to a necessity of higher dimensions just to make the maths work. So really we are guessing at the machinery of the universe

[Gordon Freynman]

Gravity does not act as a boundary. Between any two points anywhere in the universe there is a gravitational attraction. Early on gravity had a much greater affect on the universe's size but expansion has been speeding up ever since the initial laws of the universe crystallized.

The acceleration in expansion actually only started about 7 or so billion years ago. After inflation, gravity was still dominant and slowed the expansion until a critical point was reached when space expanded just enough to allow dark energy to over power gravity, and began accelerating the expansion.

[Henrik]

Universe = space?
or
Universe = space-time-and-so-on?
And how could we find out that the universe is infinite or not? Give a method, even if it's impossible to be realized.

Indeed, we can detect measure the velocity of galaxies quite a long distance away. The evidence we have now certainly suggests a Big Bang like event and a finite but boundless universe.

However, the Big Bang does not say the universe is finite or infinite.

[vlach]

Universe = space?
or
Universe = space-time-and-so-on?
And how could we find out that the universe is infinite or not? Give a method, even if it's impossible to be realized.

Indeed, we can detect measure the velocity of galaxies quite a long distance away. The evidence we have now certainly suggests a Big Bang like event and a finite but boundless universe.

However, the Big Bang does not say the universe is finite or infinite.

Maybe i haven't been clear the first time the only requirement for a universe to exist is that it contains two interacting entities so that their properties can be determined relative to each other if there is only one particle it can't interact with anything and thus is "unaware" of its own existence and cannot constitute a universe since everything in a universe has defined properties. Now the actual extent of the universe depends on the nature of the forces the particles exude on each other. Say if the maximum range of any force exuded by these 2 particles is 2 meters then the maximum extent of this 2 particle universe is 4 meters with one of these particles as the origin. Basically the span of the universe is the maximum distance from which one particle can interact with another because then both particles "know" they exist. Since we have two infinitely ranged forces the extent of the universe is infinite. This is not in contradiction with the statement of the universe being finite but boundless since these two forces cannot travel faster than the speed of light as a consequence of causality so we can say that the universe is as big as the distance traveled by light since the big bang, roughly 14 billion light years, however light will keep travelling to infinity thus there is no bound and the universe itself can be said to tend to infinity. However this says nothing of how the actual matter is distributed throughout the universe which if in equilibrium (like two unextended balls connected by a spring) will not expand and thus will give a bound on the matter filled universe (i.e. space with stuff in it) but whether or not this is the case depends on speculative factors like the density and curvature of the universe. I hope this is the type of answer you are looking for if you are trying to get a feel of the extent of the universe i have found no quantifiable answer in all my years studying physics

[Cussa]

It's just a hard concept to grasp because our brains have evolved to fathom time in hours, and days & years and maybe even centuries!

But when you get to milleniums things get a bit dodgy and beyond that in the millions and billions of years that take for the universe and life to originate, we can't even comprehend how big a time-scale that is.

When we speak of infinity, the wiring in the human brain goes all awry.

- Cussa

[Squiggle]

I was thinking earlier of why the universe couldn't of just existed without a beginning or end and then I thought of a geometry analogy that I thought put it into perspective. If the universe was truly infinite, it would be like a line. If it had a beginning and an end, then it would be a line segment. If it had a beginning with no end, the universe would become a ray.

So, doesn't the idea of a beginning and an end destroy any chance of the universe being infinite?

Also, this raises the question of what infinities would the universe require to be "infinite".

The Universe is not infinite, nor has it existed for infinity. It is finite in all manners, and has a creation point. What did you think the big bang was?!

NASA says the universe can contract too, depending "on the density and pressure of matter" in the universe. so the universe could expand forever i guess. depending on momentum of expansion or pull of gravity (gravity contracting the universe). either way it can go.

The universe could not expand forever, it is going to die.