stupid physics questions

[Dio]

I'm not sure about that. I think they're just different. You might as well argue that Newton's Laws aren't compatible with the Second Law Of Thermodynamics because the two don't overlap.

[pogo]

This is rubbish. At galactic scales, quantum mechanists make no predictions, because they know their theory, if applied, would give the wrong answers, the same is true of relativity at atomic scales. They both appear to be about as good as we can get at the scales where they do give answers that match up with reality, but they are neither of them adequate at the other end of the scale.

I don't know what you mean by 'adequate'. Both relativity and QM work everywhere. Relativity works at atomic scales, otherwise particle accelerators would not work. Quantum mechanics works at all scales: at most macroscopic scales its effects cancel out but not all. Hawking radiation is emitted by black holes due to quantum effects. We're not close enough to a black hole to detect this but I think we will be able to do so one day.

Relativity doesn't predict QM and QM doesn't predict relativity, but there's no reason they have to depend on each other. Discovering that they do would be quite a result, arguably the most significant one still outstanding in physics. But it's quite possible this will never happen: maybe there's no 'theory of everything' to discover and we'll keep using the rules we have to describe the universe.

[zip accident]

This is rubbish. At galactic scales, quantum mechanists make no predictions, because they know their theory, if applied, would give the wrong answers, the same is true of relativity at atomic scales. They both appear to be about as good as we can get at the scales where they do give answers that match up with reality, but they are neither of them adequate at the other end of the scale.

I don't know what you mean by 'adequate'. Both relativity and QM work everywhere. Relativity works at atomic scales, otherwise particle accelerators would not work. Quantum mechanics works at all scales: at most macroscopic scales its effects cancel out but not all. Hawking radiation is emitted by black holes due to quantum effects. We're not close enough to a black hole to detect this but I think we will be able to do so one day.

Relativity doesn't predict QM and QM doesn't predict relativity, but there's no reason they have to depend on each other. Discovering that they do would be quite a result, arguably the most significant one still outstanding in physics. But it's quite possible this will never happen: maybe there's no 'theory of everything' to discover and we'll keep using the rules we have to describe the universe.

If there is no "theory of everything" waiting to be discovered, then the universe is internally incoherent, or inconsistent, or something like that. Godel's theorem suggests it's a possibility, but I don't like the idea, I feel that the universe ought to be constrained by laws. If there really are laws to be found it would be a very good thing if we got on and found them IMO, and messing about tidying up Quantum Mechanics and Relativity isn't going to do that. It would be nice if the results from Betelgeuse going "bang" arrived here soon, I'd like it if there were neutrinos appearing in bursts for a couple of weeks before the light got here, then some physics might get done.

[pogo]

Gödel's theorems are about mathematics and have nothing to do with physics. E.g. Gödel's theorems are about infinity and infinite number systems while the universe is decidedly finite.

In some way there is a link though. Hilbert's program was a program to try and 'prove' all of mathematics, or at least establish a basic set of rules from which it could all be derived. Gödel showed this was impossible. Hilbert was in some ways trying to do what physicists are trying to do today, 'prove' all of physics from one set of rules. As with Hilbert there's no guarantee they'll succeed.

[Dio]

That's an incomplete view of the incompleteness theorem. There was a fascinating article about it in New Scientist early this year, that you can actually prove all of current mathematics if you bolt on a basement of additional axioms. Or something like that, I didn't really understand it .

[pogo]

Reading about it for my own interest and found this, Stephen Hawking in 2002 making the link between Gödel's theorem and physics's quest for a Theory of Everything. I'm sill not convinced though:

http://www.damtp.cam.ac.uk/events/strin ... c/hawking/

[zip accident]

Why do we call the thing/things that surround Saturn rings, when they are pretty plainly an accretion disk?

[Darkflame]

Need help!

Saw this online and its got me totally defeated:
http://endlesspicdump.com/troll-science-ferrofluid.html

Instinct says it would stabilise in the tube....but I dont know why.

If I was sucking on it, the liquid would flow out forever...what difference does a magnet make
Surely its both just a pulling action.

[5th Earth]

if the magnet was close enough to pull the ferrofluid out of the tube, it would just all stick to the magnet instead of falling down. So no perpetual motion.

[Dio]

Instinct says it would stabilise in the tube....but I dont know why.

Magnets are not sources of energy. They're a field. To leave the field you have to put energy in, entering the field allows you to get energy out.

[pasquinelli]

Gödel's theorems are about mathematics and have nothing to do with physics. E.g. Gödel's theorems are about infinity and infinite number systems while the universe is decidedly finite.

what makes you say that the universe is decidedly finite? and in what ways is it decidedly finite?

[pogo]

We think the universe started in a big bang, a long but finite time ago, and since then has been growing, sometimes much faster than now but at finite speeds, which puts an upper bound on its size. And that clearly puts an upper bound on the mass of the universe as if there were infinite mass we'd have infinite gravity and it would collapse in on itself.

It's an open question whether there's anything 'outside the universe'. E.g. whether something preceded the big bang, and it occurred in some larger pre-existing perhaps higher dimensional space. But that by definition is outside our universe.

So it may be unimaginably large and immeasurable but it is also finite.

[Darkflame]

if the magnet was close enough to pull the ferrofluid out of the tube, it would just all stick to the magnet instead of falling down. So no perpetual motion.

So there is no distance possible,ever, where the magnetic strength is enough to pull it but not enough to overcome gravity?

Would this be the same as, say, if I had a heavy toy car on a desk - too heavy for a magnet too support it - would I not be able to use a magnetic to pull it forward?
(assuming no overwealming friction)

[Dio]

Would this be the same as, say, if I had a heavy toy car on a desk - too heavy for a magnet too support it - would I not be able to use a magnetic to pull it forward?

Yes. It falls off the desk, away from the magnet, which exchanges gravitational field energy for magnetic field energy. But to do it again you have to put it back on the desk and give it the potential energy back.

[pogo]

Need help!

Saw this online and its got me totally defeated:
http://endlesspicdump.com/troll-science-ferrofluid.html

Instinct says it would stabilise in the tube....but I dont know why.

If I was sucking on it, the liquid would flow out forever...what difference does a magnet make
Surely its both just a pulling action.

One way to think of it: it's capillary action, due to surface tension and the adhesive forces of the tube, that lift the fluid. I.e. those forces are strong enough to overcome gravity, and this determines how high it will rise – it will rise until the forces of surface tension and adhesion are enough to overcome gravity for the amount of liquid lifted.

Now to pull the liquid out of the tube you need to overcome those forces: you need to supply a magnetic force greater than surface tension and adhesion both of which will act to hold it in the tube. But this means you need to provide a force greater than the gravitational force required to lift the liquid: if the magnet can pull liquid out of the tube then the magnetic force will be able to keep it from falling due to gravity.

In practice what happens might be rather more complex. A weaker magnet might deform the surface of the liquid but not be enough to pull it out of the tube. A stronger magnet might attract the liquid so it sticks, pulling it up until the magnetic field is too weak (like a magnet collecting iron filings until it can pick up no more). You could make it drop liquid by varying the magnetic field e.g. with an electromagnet but you are the supplying energy.