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Most recent answer: 10/22/2007
Q:
I have a few questions that have been on my mind constantly lately: I’ve recently read an article about the possible discovery of quark stars; if this is found to be a new state of matter, what does this say to us? Quantum mechanically. Also, I’ve read very little about neutron stars and superfluid/superconductivity. If there is no friction/viscosity, doesn’t this defy the law of conservation of energy? Is there an outer limit to the Universe? I know the universe seems to be expanding, but what if we could some how reach, and then out run the expansion of the universe? Would we hit a wall, so to speak, where space/time ends? If the universe were full of space, absent of all other forces but gravity, and only two objects existed, would gravity reach out infinitely? How far does the gravitational force reach? Last one I promise. There are 4 levels of matter that I know of: Solid, Liquid, Gas, and Plasma. To attain the next level of matter each one needs to be energized to a certain degree; increasingly more so as you go up. Is it possible that there is another state of matter?
- Ray (age 20)
Miami, FL
A:
Ray- I'll take your questions starting with the easiest for me to answer.

1. Is it possible that there is another state of matter?

Sure, there are other states of matter. You even mentioned some in your other questions. For example, if you squeeze nuclei together enough the quarks in them should form a sort of interacting quark soup, rather than separate nucleons, sort of like the way when you heat atoms enough then can form a plasma. Even under much less exotic conditions there are other states of matter. For example, liquid crystals (like in watch displays) have some properties like solids and some like liquids. Liquid crystals alone give quite a number of different states of matter, qualitatively distinct from each other.

2. If there is no friction/viscosity, doesn't this defy the law of conservation of energy?

Nope. Take a bucket of superfluid that happens to be spinning around. If there's no viscosity, it will spin the same forever, so you can directly see conservation of energy. Now take a bucket of spinning water. Thanks to viscous friction, it will gradually stop. That looks like it violates conservation of energy. Only when you figure out how to track the missing energy into thermal forms (the temperature goes up a little) do you realize that ordinary friction doesn't violate conservation of energy.

3. I've recently read an article about the possible discovery of quark stars; if this is found to be a new state of matter, what does this say to us?

I'm not an expert, but I don't think it would tell us anything very new. Quark matter was predicted on the basis of what we already believed about how quarks interact, so its discovery would only confirm the standard picture (QCD) of those interactions.

4. If the universe were full of space, absent of all other forces but gravity, and only two objects existed, would gravity reach out infinitely? How far does the gravitational force reach?

So far as we know, gravity does just trail off gradually. That's true in General Relativity and also in Newton's approximation.

5.Is there an outer limit to the Universe? I know the universe seems to be expanding, but what if we could some how reach, and then out run the expansion of the universe? Would we hit a wall, so to speak, where space/time ends?


The current pictures of our spacetime have no edges in them. We just don't know whether our spacetime is finite or infinite. If it's finite, that doesn't mean that you'll hit an edge. It means that if you and your brother set off in opposite directions, you'll meet up again.

Mike W.

(published on 10/22/2007)

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