Some questions I have about the universe...?

[Widlast]

What is the diameter of our galaxy?

The Milky Way galaxy is about 100,000 light years in diameter.

What is the diameter of the largest galaxy we know of? The smallest?

The largest listed is M87, it's about 980,000 light years in diameter, smallest is a matter of opinion.

How far away is the nearest galaxy in relation to ours? The furtherest one away that we know of?

Canis Major dwarf galaxy at about 25,000 light years distant. Furthest in WHAT direction?

Do we know how large the universe is?

It is infinite.

I'm trying to get a mental picture here...?

If we are viewing say, galaxies hundreds of billions, or trillions, of light years away, then, aren't we seeing them at hundreds of billions or trillions of years old, or earlier...

They could have fizzled out and died by now, or not even be in the/that same position, for all we know, couldn't they, if were seeing them as hundreds of billions of trillions of light years away, couldn't they?

What about a supernova of a star, say 200 light years away, do we not know it, until two hundred years later?

Some help would be greatly appreciated, thanks in advance,

God Bless!

We only know what we can see. What may or may not have happened to something which hasn't had its omitted or reflected light get here yet would be a complete mystery.

 

[hedrick]

It is infinite.

I'm reasonably sure that's not known. Indeed there's some dispute whether it's knowable.

 

[Widlast]

I'm reasonably sure that's not known. Indeed there's some dispute whether it's knowable.

A void, by its very nature is infinite. Otherwise it would necessarily be part of a larger structure.

 

[lesliedellow]

A void, by its very nature is infinite. Otherwise it would necessarily be part of a larger structure.

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." (Albert Einstein)

 

[Widlast]

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former." (Albert Einstein)

That is a very popular quote, and for good reason.

 

[lesliedellow]

That is a very popular quote, and for good reason.

Apparently he didn't think the universe had to be infinite.

 

[Widlast]

Apparently he didn't think the universe had to be infinite.

He didn't think that an expanding universe was real either and fudged his own data to suit his whims.

 

[lesliedellow]

He didn't think that an expanding universe was real either and fudged his own data to suit his whims.

He changed his mind in the light of newly available data.

 

[hedrick]

A void, by its very nature is infinite. Otherwise it would necessarily be part of a larger structure.

Not true. There are possible topologies that are closed.

 

[TagliatelliMonster]

About speed and time, is it as Einstein says that the closer you get to the speed of light, time slows down or even stops at the speed of light...?

Relative to an outside observer.

Suppose you step in a spaceship and travel at great speed around the solar system.
Right before you leave, you sync your watch with one that stays on earth.
Upon your return, more time will have passed according to the watch on earth, as opposed to the watch that you took with you.

This is why the internal clocks of GPS satellites are calibrated to run slower then those on earth, to make up for the relativistic effects.

Without that calibration, GPS would be off several miles.

 

[TagliatelliMonster]

One of the most inspiring space pictures imo.

 

[Larniavc]

How much space is there between galaxies? Are they far apart like star systems are in galaxies, or not so much?

It is 2.537 million light years to the Andromeda galaxy.

 

[Larniavc]

Is the universe really expanding, like an explosion is or does, and will it slow down and fizzle out like and explosion does, in time...

It's not expanding like an explosion from a central point.

All distances not bound by gravity are increasing.

 

[Larniavc]

Please ignore.

 

[hedrick]

It's not expanding like an explosion from a central point.

All distances not bound by gravity are increasing.

right. It's not an explosion. Imagine a bomb sitting in the middle of a large field. When the bomb explodes the fragments of the bomb scatter, so in some sense the bomb gets bigger, but the field stays the same size.

In this case it's space itself that is expanding. The best analogy is a balloon. Imagine you're living on the surface of a balloon, and someone is blowing it up. The distances in your world will all be expanding.

As far as anyone can tell, the forces driving the process are still there. It's not like an explosion, where all the force happens at the beginning. In this case whatever is driving the expansion is continuing to do so.

 

[Widlast]

Not true. There are possible topologies that are closed.

You are making the assumption that the Universe is an "object" and that the notion of topology even applies.
I do not make that assumption, notice I said "void".

 

[lesliedellow]

You are making the assumption that the Universe is an "object" and that the notion of topology even applies.
I do not make that assumption, notice I said "void".

The notion of topology applies wherever there are sets. Specifically it applies to sets of points in spacetime.

 

[Neogaia777]

right. It's not an explosion. Imagine a bomb sitting in the middle of a large field. When the bomb explodes the fragments of the bomb scatter, so in some sense the bomb gets bigger, but the field stays the same size.

In this case it's space itself that is expanding. The best analogy is a balloon. Imagine you're living on the surface of a balloon, and someone is blowing it up. The distances in your world will all be expanding.

As far as anyone can tell, the forces driving the process are still there. It's not like an explosion, where all the force happens at the beginning. In this case whatever is driving the expansion is continuing to do so.

What is the driving force behind, or who is blowing up the balloon...?

Is it expanding at a steady rate, or slowing down or getting faster...? Is there a definable center, or not?

 

[Neogaia777]

Thanks to the rest of you for your replies...

God Bless!

 

[hedrick]

What is the driving force behind, or who is blowing up the balloon...?

Is it expanding at a steady rate, or slowing down or getting faster...? Is there a definable center, or not?

Here's a good explanation: Accelerating expansion of the universe - Wikipedia

No one is sure what is causing the expansion. There are pretty good mathematical models of the expansion, but they involve a constant that's just put in the model to make it fit observation. It's not clear what the physical explanation of it is.

Wikipedia notes "The simplest explanation for dark energy is that it is simply the "cost of having space": that is, a volume of space has some intrinsic, fundamental energy. ... In fact, most theories of particle physics predict vacuum fluctuations that would give the vacuum this sort of energy." But there are problems with that explanation, as noted in the article, and there are other possibilities. This is an area that many people are working on.

The rate appears to be increasing, though I wouldn't consider that a final result. There wouldn't be a center, because all of space is expanding. Every point is going away from every other point.

The fact that we don't have a complete explanation doesn't mean it might not be happening. There are plenty of things that we know happen even if we can't explain them.