How do we know the universe is infinite?

Is it really? I was of the impression mass decided it’s limit, but that it could expand infinitely.

Edit: But I guess you mean beyond the universe? That is mind boggling. I guess you are right, in that it extends our level of comprehension. For now.

because we don’t know is probably why we “know” it.. in a sense, we just have faith that it is based on the evidence thus far.

Because we haven’t eaten at the restaurant at the end of the universe yet..

Personally, I feel there is no end to it. That it just keeps going and going and going…kinda like the energizer bunny but in a much larger capacity

It’s hard to imagine the absence of space-time “wherever” the universe has not yet reached in its expansion. There’s no there there, as Gertrude Stein once said of Oakland, CA.

We don’t. There is ongoing scientific debate as to whether the universe is open and infinite, or closed in on itself.

Because it’s expanding. So if it never ends then it’s infinite.

oh goodness…my head hurts again…but I love these topics…

urrrrrrrm….I’m going to sleep on this one…. :-/

No matter how far you go, you can always go farther.

Well technically we should be able to reach the “end of time”. In the sense that sine time is a measure of movement and movement cannot exist without heat, if we go far enough from any star we should, eventually, reach a place where we go lower than absolute zero thus freezing the atoms in place and ending our perception of time.

Then again since the universe is expanding we’d unfreeze sooner or later…

@Thammuz You can’t go lower than absolute zero.

@oratio We haven’t even gotten there yet.

@Drawkward Right. Nothing in the universe has been shown to reach absolute zero.

Also, @Thammuz, time is not a measure of movement, it is a dimension just like the spacial dimensions, and just as you can move east without moving north, you can move through time without moving through space.

@pdworkin Stein’s comment is often misunderstood. What she meant was that the house she grew up in had been torn down.
I hecka love Oakland.

Because Physicists tell us that it is. Physicists are smart.

If the universe is infinite… then what is it expanding into? To expand seems to imply there is something beyond it. Something empty that is being filled. But an infinite universe means that it never ends so should fill everything that there is already.

I have to stop thinking about this. The universe is one of those serious mindf**k things for me.

The universe is not infinite. One of the most popular interpretations of General Relativity says that the universe is bounded, but limitless. It has a finite size, which is expanding, but you may travel forever in a any direction without reaching a barrier. Much like walking/sailing around the Earth. Given appropriate equipment you will never reach an impassable barrier, but the Earth’s surface area is known.

This may be a useful article.

@Supacase sounds to have hit the nail for me…

@Jayne As far as i know that was one of the possibilities for the fourth dimention. As for time not being a measure of movement, no it is not a measure of movement, it is a measure of events. We measure time in relation to reality changing around us, we use quartz atoms as a reference and, although it doesn’t necessarily have to be quartz, we need that reference.

If every atom in the universe suddenly froze into position, nothing moved from its position at moment x, including subatomic particles and quanti, and stayed so for a thousand years only to resume its movement with unaltered momentum, whould we notice? I don’t think so.

@FireMadeFlesh “Why should three dimensions be infinite while others are finite?”

Very interesting.

We don’t know anything about the whole cosmos. We might live in a multiverse. We might live in a baby universe which is part of a hyperverse. The possibilities are endless.

@mattbrowne As the possibilities are endless, it makes me wonder if we will ever learn the truth about the universe. Maybe it is not for us to find out, but for they who come after us.

It won’t matter. They will die with their knowledge.

@oratio Those who come after us will know less than we do. We are living in a special period of history, when we can still know the beginning and yet know the end. Those who come after us (well, very distantly after) won’t even be able to tell that the universe is expanding; all they will know is that Thermodynamics is slowly killing them.

@pdworkin Then what is the point of any knowledge? We will die with ours, so should we not seek knowledge just because we will die?

I was just in a pissy mood.

@FireMadeFlesh I am not sure about what you referred to with your comment. I can only assume that either you talk about devolving or the total disappearance of humanity. Even if that would happen, there would most likely eventually arise another intelligent species.

I agree to that it is a special period – as far as we know – in our planets history, but we have only existed for a couple of seconds of the day of life on earth. Before us was other human races, and we are only the latest model. There will be another coming. Probably several, depending on what you deem as life. Artificial sentience will most likely occur, and what is that if not an aspect of our human evolution. We will be here a long time, but as evolution has sped up, we will see change in time, on a biological level.

We are the crown jewels of evolution, though I very much doubt that we are at the maximum possible height of consciousness and awareness.

@oratio I am not referring to devolving or total disappearance of humanity in particular, I am referring to the death of the universe. The universe is expanding at an ever increasing rate, which means a few hundred million years from now we will be unable to observe any celestial object currently moving away from us. There will be no trace left, as they will cross an event horizon, leaving only our local cluster which is too tightly bound by gravity.

It has been shown that because of this event horizon, future generations will be unable to detect the expansion of the universe, because all the effects of this expansion will be in an unobservable region of the universe. Other phenomena, such as the acceleration of the expansion, would not have been observable in earlier times. Therefore we live in a special time – the only time in history when we may be scientifically certain of both the beginning and the end of the universe.

I agree that it is likely that intelligent life will be around for many millions of years more, but eventually the universe will kill us all.

@FireMadeFlesh Lol, very true.

@oratio – Maybe. Although I don’t believe in the technological singularity I do believe in accelerating global intelligence. More secrets about the cosmos will be revealed.

We know that the Universe is not infinite. If it were, there would be an infinite number of stars and galaxies in it. While stars seem smaller and smaller at greater and greater distances, the light they send our way is still equally bright. Sop if there were an infinite number of them, the nighttime sly would not have any dark spots. THe enture nighttime sky would be lit up like the brightest star. Since it is not, we know the universe is not infinitely large.

@ETpro http://www.universetoday.com/73567/hubble-deep-field/ Doesn’t seem that all stars are visible, at least not to the naked eye.

@Thammuz Indeed they are not. However, imagine if pixels could be infinitesimally small. Since it is light we are dealing with, imagine that each pixel is exactly one photon (a point particle with no size) in diameter. Now imagine that the entire night sky were made up of lit up pixels. You then would see a sky that looks just like a large flat screen TV with every pixel lit up brightly. The only difference is each of these pixels would be infinitely small, but there would be an infinite number of them so they would still blanket the entire sky.

Since we don’t see a sky like that, the Universe appears not to be infinitely large with an infinite number of stars and galaxies.

@ETpro Ooook, that makes more sense now, thank you.

@ETpro could it not be infinitely large without being infinitely full? Or could there be an infinite number of stars that formed a finite amount of time ago, and therefore the light from the further ones has simply not reached us yet?

@RareDenver Infinity is a difficult concept to wrap a finite mind around. Anything infinite is so large that if you cut it in half, or in tenths, or divided it any amount of times, what you would have left would still be infinite. In other words, it doesn’t exist in finite worlds. Spacetime is not a vast void beyond the last stars, it is the matter-energy-space-time Universe. It has to have things like stars in it to exist. And if it were infinite, that would still be so.

It is an easier stretch of the imagination to believe the universe is without end rather than it having an end of some sort. There are theists who believe that “god” is eternal, everlasting, without end. Contemplating the limits of the universe is the same thing.