stupid physics questions

[zip accident]

Well, it's only tangentially physical, barely that I suppose, however.

The Tower of Babel ... "whose top may reach unto heaven; ..."

http://en.wikipedia.org/wiki/Tower_of_Babel

That's a space elevator isn't it? Funny how such things turn up in such old stories.

[Darkflame]

Is there any theory which basically postulates that there is no such thing as variable mass? That is, everything has the same mass, only we see stuff in different densities?

I was reading stuff about the equivalence principle, and its so called "coincidence" in a recent issue of the New Scientist, and it struck me as a possibility someone must have looked at.

When you have two identical objects its obviously they will fall towards the ground at the same time. If you put a tiny bit of glue connecting them and declare them now as "one object", it wont effect the speed. You have just reclassified what you call "an object" rather then really changed anything.
So course a big ball of lead and two small balls of lead will all hit the ground at once - its just a collection of lead atoms arbitrary arranged.

Could the whole of the material world be like this? That what we perceive as different atoms with different atomic masses are just fundamentally "the same mass" and thus it falls at the same rate regardless of how on the macro scale we group and name things.

[Portland]

http://xkcd.com/1166/

Couldn't help think of this and similar threads on Yak and other places

[zip accident]

Not so much a question exactly, but certainly stupid with our current level of technology.

Black holes as a starship drive.

You obviously can't move a big one, and a small one spews energy too fast to be safe. However, if you could make a setup to almost make one, that would make one with the addition of matter, then you could bung matter in slowly, and you'd get energy out, so if you could direct that, you would have a drive (or heating, if you didn't bother directing it).

[zip accident]

What happens when dark matter meets a black hole?

Dark matter allegedly doesn't interact with matter except via gravity. However, gravity is about all a black hole has. Can dark matter escape from a black hole, if so how since it is affected by gravity?

[pogo]

Fuck knows as no-one has a clue what dark matter is. Just read this

https://en.wikipedia.org/wiki/Dark_matt ... omposition

More precisely there are lots of theories but not of them confirmed by observation. E.g. they don't think it's normal matter of the sort that makes stars and planets but then what is it and where does it fit into models for subatomic particles, and how do we detect it (apart from gravitationally on a galactic scale)? The massive particles we know about are either normal matter, neutrinos which go to fast to form the clumps of matter we can detect, or exotic heavy particle which are unstable and decay.

[zip accident]

Fuck knows as no-one has a clue what dark matter is. Just read this

https://en.wikipedia.org/wiki/Dark_matt ... omposition

More precisely there are lots of theories but not of them confirmed by observation. E.g. they don't think it's normal matter of the sort that makes stars and planets but then what is it and where does it fit into models for subatomic particles, and how do we detect it (apart from gravitationally on a galactic scale)? The massive particles we know about are either normal matter, neutrinos which go to fast to form the clumps of matter we can detect, or exotic heavy particle which are unstable and decay.

Yeah, I know most of what you wrote, but a if a neutrino went into a black hole it couldn't get out again, which I think is interesting. I'm just off to read your link.

[pogo]

What we know and understand about black holes is described in terms of normal matter. Neutrinos are normal matter (in that we know where we fit in) but they don't think dark matter is made of them: they move too fast, at the speed of light, to form the stable clumps of dark matter that we can detect. The most plausible theory is WIMPs, weakly interacting massive particles. Weakly interacting means they don't experience fundamental forces, so they don't form atoms, we can't see them, they don't get deflected by magnetic fields, etc.. But if so what are they?

The other possibility is there's no such thing. Dark matter isn't a real thing but it's a fudge factor in our equations because we don't fully understand how gravity and the universe works on galactic scales. We're very confident relativity is correct but can only confirm it directly within our solar system. Maybe something else comes into play as you move into interstellar space.

[zip accident]

What we know and understand about black holes is described in terms of normal matter. Neutrinos are normal matter (in that we know where we fit in) but they don't think dark matter is made of them: they move too fast, at the speed of light, to form the stable clumps of dark matter that we can detect. The most plausible theory is WIMPs, weakly interacting massive particles. Weakly interacting means they don't experience fundamental forces, so they don't form atoms, we can't see them, they don't get deflected by magnetic fields, etc.. But if so what are they?

WIMPs are affected by gravity though, since they affect it. Which means, unless they are FTL capable, if they fall into black holes, they can't get out again.

<edit>

Actually, I do like the FTL option. It covers so many things. If "c" as a limit is due to the electro-magnetic forces etc., and WIMPs are unaffected by electro-magnetic forces, the extra speed from falling into an event horizon would also take them back out.

</edit>

The other possibility is there's no such thing. Dark matter isn't a real thing but it's a fudge factor in our equations because we don't fully understand how gravity and the universe works on galactic scales. We're very confident relativity is correct but can only confirm it directly within our solar system. Maybe something else comes into play as you move into interstellar space.

There is that option.

[pogo]

Well, saying they're "weakly interacting massive particles" is shorthand for saying "we haven't a clue what they are". So maybe they interact after all, but only very rarely. But they'll have lots of chances to do that at the infinitely dense heart of a black hole. Maybe the conditions at the centre of the black hole change their behaviour so they get stopped. We don't know, it's pure speculation. It's not just that we don't know what they are but we think we know all the particles there are*, we've detected them all (the Higgs boson was the last), and none is a good candidate for a WIMP. Any WIMP is both undetectable and outside our understanding of particle physics.

*: https://en.wikipedia.org/wiki/Standard_Model

edit: and FTL travel simply isn't possible. If it were then time travel would also be possible, which disagrees with most people's sense of a well ordered universe. The only vaguely plausible model for faster than light is tachyons which don't interact with anything, including gravitationally. Plus anything going so fast could not be dark matter which exists in clumps but without enough mass to stop light and light-speed (or faster) particles escaping. For the same reason WIMPs are very unlikely to be neutrinos, a shame as apart from going too fast they have the right properties (they don't interact much and are hard to detect).

[Absolute_Zero]

Well, saying they're "weakly interacting massive particles" is shorthand for saying "we haven't a clue what they are". So maybe they interact after all, but only very rarely. But they'll have lots of chances to do that at the infinitely dense heart of a black hole. Maybe the conditions at the centre of the black hole change their behaviour so they get stopped. We don't know, it's pure speculation. It's not just that we don't know what they are but we think we know all the particles there are*, we've detected them all (the Higgs boson was the last), and none is a good candidate for a WIMP. Any WIMP is both undetectable and outside our understanding of particle physics.

*: https://en.wikipedia.org/wiki/Standard_Model

Depends... if you're sympathetic to SUSY (supersymetry) then there's a whole shitload yet to be made manifest. With regard to Dark Matter, that would be the family of neutralinos.

Speaking of which, just this week...
http://motls.blogspot.co.uk/2013/04/ams ... s.html?m=1

[zip accident]

Well, saying they're "weakly interacting massive particles" is shorthand for saying "we haven't a clue what they are".

Yeah, that's why I suggest exotic behaviour.

So maybe they interact after all, but only very rarely. But they'll have lots of chances to do that at the infinitely dense heart of a black hole.

The reason everything ends up at the singularity is that if c is a limit they can't be accelerated any faster once they reach c, which inside the event horizon is a given. According to most guesses about black holes, inside is entirely space except for the infinitesimal singularity.

Maybe the conditions at the centre of the black hole change their behaviour so they get stopped. ... Any WIMP is both undetectable and outside our understanding of particle physics.

Maybe they don't get stopped in black holes. The reason I like the "they don't get eaten even if they enter a black hole" option, is that there are a large number of SMBHs, and if these particles got converted from exotic matter to baryonic matter by being consumed, I would expect more baryonic mass and less dark matter.

edit: and FTL travel simply isn't possible. If it were then time travel would also be possible, which disagrees with most people's sense of a well ordered universe. The only vaguely plausible model for faster than light is tachyons which don't interact with anything, including gravitationally. Plus anything going so fast could not be dark matter which exists in clumps but without enough mass to stop light and light-speed (or faster) particles escaping. For the same reason WIMPs are very unlikely to be neutrinos, a shame as apart from going too fast they have the right properties (they don't interact much and are hard to detect).

I'm not talking about FTL travel for anything baryonic. These are very exotic particles, and maybe they do exotic things. I don't think you can limit them to exceeding c only inside the event horizon of a black hole, if they were travelling fast enough on their approach they would need to exceed c before getting that close. However maybe the time travel aspect keeps them entirely clear of the event horizon.

[pogo]

Definitely nothing can go faster than c. Even dark matter, as we can detect it gravitationally (if only on a galactic scale), so if it could go faster than light it would violate causality. Besides we're pretty sure dark matter doesn't approach light speed, as if it did it would easily escape the galaxies it's associated with, not clump together in them.

Speculating about the properties of 'exotic' matter is pretty pointless, like asking how many angels can dance on the head of a pin. My own favourite theory on dark matter is it's just baryonic, i.e. regular, matter. Space is unknowably vast and we have a hard time spotting even large rocks in our own solar system. Why can't there be other things out there that we can't see that account for the missing mass? It might even be black holes, or at least some of it: away from stars these should be impossible to spot unless one happens to get in front of another star.

[zip accident]

Definitely nothing can go faster than c. Even dark matter, as we can detect it gravitationally (if only on a galactic scale), so if it could go faster than light it would violate causality.

It/they would (perhaps?) only violate causality if it interacted while FTL.

Besides we're pretty sure dark matter doesn't approach light speed, as if it did it would easily escape the galaxies it's associated with, not clump together in them.

I am talking about exceeding the speed of light while being accelerated under gravity toward the singularity of a black hole. It would be deccelerated to approximately the same extent as it left the black hole, so it's speed through normal space would be normal, maybe somewhat random. I'm thinking of a particle a bit like a neutron with no definite speed (but also, obviously, in other ways markedly unlike a neutron).

Speculating about the properties of 'exotic' matter is pretty pointless, like asking how many angels can dance on the head of a pin.

Sure, it is speculation, but I hope it's not aimless speculation. I am a fan of science fiction, but I do prefer it kept within the bounds of the scientifically possible, which means working out where those bounds are is interesting.

My own favourite theory on dark matter is it's just baryonic, i.e. regular, matter. Space is unknowably vast and we have a hard time spotting even large rocks in our own solar system. Why can't there be other things out there that we can't see that account for the missing mass? It might even be black holes, or at least some of it: away from stars these should be impossible to spot unless one happens to get in front of another star.

I think that they currently think that dark matter isn't baryonic.

[zip accident]

Now they're just taking the piss.

http://news.sciencemag.org/sciencenow/2 ... tml?ref=hp

Via /.

When does quantum physics come out as magic?