Ask a physicist anything. (7)

[mzungu]

I don't quite know what you mean here.

Sorry I was a little vague there; I meant: Can photons be split !

 

[Mr. Pedantic]

More mass means more gravity is 'pulling' on spacetime, counteracting its expansion.

From what I understood the expansion of the universe was not from objects moving away from each other per se, it was from the creation of space between these objects.

If this is true, then wouldn't the contraction of the universe due to gravity cause bits of nothing around the edges, where the universe continues to expand, but there is no matter left because of the effect of gravity?

 

[Chalnoth]

Sorry I was a little vague there; I meant: Can photons be split !

Well, if they're really high in energy, sort of. If two photons smack into one another with a rest-frame energy of more than twice the mass of the electron, the two photons can produce an electron-positron pair. That's sorta-kinda splitting, I guess?

But no, there are almost certainly no separate components of a photon.

 

[Chalnoth]

From what I understood the expansion of the universe was not from objects moving away from each other per se, it was from the creation of space between these objects.

If this is true, then wouldn't the contraction of the universe due to gravity cause bits of nothing around the edges, where the universe continues to expand, but there is no matter left because of the effect of gravity?

Well, to have that, you'd need to have edges in the first place. I'm not so sure that such edges make sense. It may be more likely, for example, that the universe wraps back on itself, somewhat like the surface of a sphere.

 

[Chalnoth]

OH MY GOOD LORD!!!!!!! I dedicate this video to all our CREATIONIST friends (Miss Vermont is the only one voting for the Democrats the rest are Republicans)"math is a theory and it is not what the Bible tells us" :

Miss USA 2011 — Should Math Be Taught In Schools? - YouTube

Does America have any education in her schools any more?

Miss USA - Should Gravity be Taught in Schools? - YouTube

Just in case it wasn't entirely clear, these two videos are parodies of this clip of an actual question asked:
Miss USA 2011 - 51 Delegates Interview (Q2 - Evolution taught in school) - YouTube

 

[Mr. Pedantic]

Well, to have that, you'd need to have edges in the first place. I'm not so sure that such edges make sense. It may be more likely, for example, that the universe wraps back on itself, somewhat like the surface of a sphere.

In this case, where is the center of gravity?

 

[Chalnoth]

In this case, where is the center of gravity?

That's the frame where the two photons have the same frequency, but are traveling in exact opposite directions.

 

[Mr. Pedantic]

That's the frame where the two photons have the same frequency, but are traveling in exact opposite directions.

...eh?

 

[Chalnoth]

...eh?

Ack, darn it. I've answered the wrong question.

Sorry, I assumed you were responding to a different post. Okay, on a universe that wraps back on itself, there is no center of gravity.

 

[Mr. Pedantic]

Ack, darn it. I've answered the wrong question.

Sorry, I assumed you were responding to a different post. Okay, on a universe that wraps back on itself, there is no center of gravity.

Then what is the point of contraction of the universe? Where does the matter go?

 

[Chalnoth]

Then what is the point of contraction of the universe? Where does the matter go?

The contraction just has the distances between all the bits of matter getting smaller. There is no center to this motion, just as there is no center to expansion.

 

[Mr. Pedantic]

The contraction just has the distances between all the bits of matter getting smaller. There is no center to this motion, just as there is no center to expansion.

How does this happen without a center of gravity?

 

[Chalnoth]

How does this happen without a center of gravity?

Well, it works the same way whether it's Newtonian gravity or General Relativity.

Basically, all of the matter attracts all of the other matter. So gravity wants to make all of the matter closer together. There doesn't need to be a center for it to work this way.

 

[chris4243]

Then what is the point of contraction of the universe? Where does the matter go?

Everywhere, or nowhere depending on what you think of such things. The center of a closed universe would be outside the universe in a different dimension that may or may not actually exist. Like if you pretend the universe is the surface of a balloon, it can expand and contract but there is no center, or the center is not on the surface of the balloon. It's possible to do the maths for a curved surface without any extra dimension for the curvature to exist in, but it is hard to visualize because it means lines aren't straight.

If the universe is open (infinite), then there would also be no center.

 

[RickG]

Everywhere, or nowhere depending on what you think of such things. The center of a closed universe would be outside the universe in a different dimension that may or may not actually exist. Like if you pretend the universe is the surface of a balloon, it can expand and contract but there is no center, or the center is not on the surface of the balloon. It's possible to do the maths for a curved surface without any extra dimension for the curvature to exist in, but it is hard to visualize because it means lines aren't straight.

If the universe is open (infinite), then there would also be no center.

My understanding is that the current consensus among astrophysicists is that the universe is not only expanding, but that expansion is speeding up, possibly due to "dark energy".

 

[Steffenfield]

The track pad on my gf's Blackberry Curve 9330 is nonresponsive.

I took it apart, put it back together again, but no dice.

What might be the cause of this?

Also, what would be the best method on cleaning it?

Cheers boys.

 

[Mr. Pedantic]

Everywhere, or nowhere depending on what you think of such things. The center of a closed universe would be outside the universe in a different dimension that may or may not actually exist. Like if you pretend the universe is the surface of a balloon, it can expand and contract but there is no center, or the center is not on the surface of the balloon. It's possible to do the maths for a curved surface without any extra dimension for the curvature to exist in, but it is hard to visualize because it means lines aren't straight.

If the universe is open (infinite), then there would also be no center.

Then what is the significance of the matter in the universe contracting under gravity if it moves nowhere?

Well, it works the same way whether it's Newtonian gravity or General Relativity.

Basically, all of the matter attracts all of the other matter. So gravity wants to make all of the matter closer together. There doesn't need to be a center for it to work this way.

Then which way does the matter go?

 

[Chalnoth]

Then which way does the matter go?

I don't really know that I can make this any clearer. The matter gets closer together. That is the only statement that you can sensibly make. There is no center, so your question doesn't make sense.

 

[Nostromo]

The track pad on my gf's Blackberry Curve 9330 is nonresponsive.

I took it apart, put it back together again, but no dice.

What might be the cause of this?

Also, what would be the best method on cleaning it?

Cheers boys.

Apparently it's a common problem and may be due to a faulty batch of track pads, if it's still under warranty (ignoring the fact that you took it apart) it might be best to see if you could get it replaced.

Cleaning, I don't know, there's not much to clean as the trackpad is essentially an upside down optical mouse. If the surface is all scratched up that might affect it, polishing it might help, probably best to Google for tips on that.

P.S. I find it a little odd that you just happened to have a T6 screwdriver lying around.

 

[mzungu]

How does this happen without a center of gravity?

much like the universe being the surface of an expanding balloon; there is no centre!