Does the universe have a boundary?

[Mazerakham]

Does the universe have a boundary--i.e. if we could go out "sufficiently far" in some direction, would we eventually hit some barrier preventing us from going further?

Theories anyone?

 

[bucky1andonly]

No boundaries. Why, because the universe is mostly nothing. Nothing only exists when there is a lack of something :P So you would eventually travel and reach the end of stuff and hit the void of nothingness, and continuing to travel further away from the nearest star, if you managed to get so far so that you can't see any light from stars, you could never know if you were at a boundary or not anyway. There is a boundary, but that is when the void of nothingness begins.
(scientific term - stuff :P)

 

[Mazerakham]

Good reasoning. And intuitively, I would agree.

But why, then, do we theorize about a "beginning" to the universe. If it is intuitively obvious that the dimensions of space extend infinitely in every direction, then shouldn't time also extend infinitely? It makes no more sense to me that there should be a beginning of time. No more sense than that there should be an end (since the direction of time is a human perception anyway).

Is there anything wrong with the (albeit, unprovable) hypothesis that any "thing" (piece of matter or energy?) which exists now always has existed and always will exist?

 

[DaveC426913]

No boundaries.

True.

Why, because the universe is mostly nothing.

True but irrelevant.

So you would eventually travel and reach the end of stuff and hit the void of nothingness,

False.

You can never reach of the "end" of the observable universe; the universe's farthest regions are expanding faster than the speed of light. No matter how fast you travel, the observable edge of the universe will continue to expand faster.

Whatever is outside the observable universe is forever beyond our perception.

if you managed to get so far so that you can't see any light from stars,

Not merely false, but - no offense intended - kind of naive.

If it is intuitively obvious that the dimensions of space extend infinitely in every direction, then shouldn't time also extend infinitely?

No, because it is a time-like dimension, which is different than a space-like dimension in the very property that it is not infinite, and only extends in one direction: forward.

 

[Nabeshin]

Current data indicates that the universe is flat. However, the topology could either be similar to euclidian flat space or that of a torus; one is infinite the other is not.

 

[bucky1andonly]

Just because we can't travel faster than the speed of light right now, doesn't mean we would never be able to. With that in mind, reaching the end of the observable universe would be possible, and to continue into the void where matter hasn't been yet would also be possible, although it would take an unthinkable amount of time.

Whatever is outside the observable universe is forever beyond our perception

This is why we are theorizing, there is no right or wrong answers only opinions. For all we know, there were hundreds of thousands of bigbangs all over the universe and when we reach the boundary of our bigbang area, we could very well end up in another.

And time, is just a measurement, nothing more. Time can be altered though, just like a kilogram or kilometer could be. We set the rules for how long something is or how heavy in relation to something else. Time is just a measurement of how long a rotation around the sun and revolution of the Earth takes broken down for the sake of people. If the Earth's rotation around the sun slowed down, we would have to alter our calenders to match the extra days gained. I just looked up what stardates on star trek mean, and they mean nothing, which makes sense, because traveling through space, how do you keep track of time without a point of reference. You would have to use Earth time obviously.

 

[russ_watters]

Just because we can't travel faster than the speed of light right now, doesn't mean we would never be able to.

That's probably not true. By our current understanding, with an extrordinarily strong experimental basis, the laws of the univese forbid FTL travel.

With that in mind, reaching the end of the observable universe would be possible, and to continue into the void where matter hasn't been yet would also be possible, although it would take an unthinkable amount of time.

You're not understanding. No matter how fast we go, the universe will never look fundamentally different where we are from where we've been. There are no completely empty spaces beyond where matter exists.

This is why we are theorizing, there is no right or wrong answers only opinions. For all we know, there were hundreds of thousands of bigbangs all over the universe and when we reach the boundary of our bigbang area, we could very well end up in another.

Right and wrong is the domain of philsophy. In science, we only have what matches what we observe and what doesn't. What you describe does not match what we observe.

And time, is just a measurement, nothing more.

Sort of - it is a dimension.

Time can be altered though, just like a kilogram or kilometer could be. We set the rules for how long something is or how heavy in relation to something else. Time is just a measurement of how long a rotation around the sun and revolution of the Earth takes broken down for the sake of people. If the Earth's rotation around the sun slowed down, we would have to alter our calenders to match the extra days gained.

No. We can define a "second", but that does not have any influence on the real rate of the passage of time. You must already intuitively know this: an object that is 2.54 cm long is also 1 inch long. Changing the units does not change the real length of the object.

 

[bucky1andonly]

There are no completely empty spaces beyond where matter exists.

Without knowing more about the universe, no one can say there is no completely empty spaces beyond where matter exists. We just cannot see that far.

No. We can define a "second", but that does not have any influence on the real rate of the passage of time. You must already intuitively know this: an object that is 2.54 cm long is also 1 inch long. Changing the units does not change the real length of the object.

Exactly, you can't change how long something is (besides cutting it) but the original length of something is absolute, just like time. Also, I don't like thinking time as a dimension, then you get into the whole dimensional travel crap, which in theory, is more realistic than time travel, which can never exist. If time is a dimension, then how do you define the origin. Bigbang couldn't have created time, time existed before that. Time will always exist, due to the fact it is merely a measurement. No different then putting one meter stick in front of another endlessly.

 

[russ_watters]

Without knowing more about the universe, no one can say there is no completely empty spaces beyond where matter exists. We just cannot see that far.

Ok, well then we should just say that current theory predicts that there are no completely empty spaces beyond where matter exists. It's still wrong to claim such spaces exists.

Exactly, you can't change how long something is (besides cutting it) but the original length of something is absolute, just like time. Also, I don't like thinking time as a dimension, then you get into the whole dimensional travel crap, which in theory, is more realistic than time travel, which can never exist. If time is a dimension, then how do you define the origin. Bigbang couldn't have created time, time existed before that. Time will always exist, due to the fact it is merely a measurement. No different then putting one meter stick in front of another endlessly.

Sorry, most of that is wrong too. Time - and the other, spatial dimensions - were created at the big bang. And as with the other dimensions, you define your origin wherever is convenient for your needs. It's relative to your chosen frame of reference. Also, length (and time) is relative in that two observers may not agree on the length of an object or time between two events.