/sci/ - Science & Math

>>6399376
well done OP. But couldn't you get this from moddin de Sitter-Schwartzschild?

>>6399374
in relation to what? Velocity of distant objects is in general not defined in curved spacetime. In an inertial reference frame on the horizon, the mirror is moving always slower than light. Note that incoming light reflected from this mirror in the moment it passes the horizon will hover on the horizon forever for an external observer.

>>6399348
>Fact 1: Mirrors repel light.
no

>Fact 2: Light cannot escape a black hole.

ok

>What would happen if we (hypothetically) covered the surface of a black hole with mirrors?

Fact 3: you can't hold a mirror on the event horizon. It will fall inside.

yeah, radius-wise, it's not that big of a ratio. That's the whole point of precession of the equinoxes.

This also makes clear how big jupiter is, and why it affects celestial dynamics so much.

Mass-wise, it's fucking huge.

>>6399169
you're being multiple variously large douchebags

>>6399132
not necessarily. Also, field lagrangian mechanics is definitely more advanced than CED and special relativity, and might be at most included at the end of such a course.

This thing can be done without the ion cannon, like some people did a while ago when coming up with the theory of relativity.

>>6398536
>>6398557
>>6398660
>>6398664
>>6398674
>>6398820
you're being a fucking douchebag. He doesn't need to understand the goddamn variational approach for fields. He doesn't need to ask in the QFT thread. He just need the explicit proof of covariance of Maxwell's Equation in vector form.

Here, OP, check any text on special relativity or classical electrodynamics, I suggest Prof Bo Thid?'s book (It's a draft and should be on his site) and you will find a clear proof.

The idea is finding how derivatives in time and space transform under a lorentz boost (invariance under translation and rotations is evident) and then trying to find how E and B should trasform to make the new equation look like the old but with E' and B'.

Note that Maxwell's equations in matter are NOT covariant because of the preferential frame given by the material itself.

>>6398496
no? A quantum particle (in this case, 2 degrees of freedom) is not a quantum field (infinite degrees of freedom)

>>6397930
OH JESUS CHRIST GODDAMMIT

>>6397785
what are you referring to? That was a mathematical statements about spacetimes. What does QM have to do with it?

>>6397832
>>6397843
your personal opinion on the definition is not relevant in science. The definition is the presence of closed time-like curves.

>>6397768
this is immensely helpful. Thank you. Fucking saved.

>>6397682
a bh and a time-flipped bh have the same metric, but a different time orientation, so they are not the same spacetime (though the same pseudomanifold)

>>6397627

>Negative time with positive energy is homologous to negative energy with positive time, and afaik there is no reason why negative energy density should be impossible.

no, it doesn't work like that. Energy density is not a pseudoscalar, it's the time-time component of a tensor.

>There is no confirmed mechanism to exceed the positive energy in the surrounding area, if the Casimir effect counts, and it could destroy the universe, if the inflaton field is erratic, as string theory predicts (and which could still be true without string theory).

sorry, I can't make sense of this sentence, sintactically. And I don't see how the phenomena mentioned have any relevance.


>Mirroring in time would do that, but that's not a Lorentz transformation so it's not trivial that doing that is allowed. I'm don't know how the connection works between black and white holes.

jesus fucking christ, 1) time reversal WOULD BE a lorentz transformation, and 2) there are no Lorentz transformations in a curved spacetime. This is CRUCIAL. Any diffeomorphism is allowed in GR, it's the gauge symmetry itself.

>If you can connect a black hole to a black hole, however, I see no reason why you couldn't have particles traverse the wormhole anyway (beyond normal wormhole stuff, that is).

Because the wormhole dismantles before they can go through, so there are no timelike (nor lightlike) wordlines going into one mouth and out the other.

>>6397658
>implying that the standard proof of conservation of mechanical energy isn't just a simplification of a special case of noether's theorem
>implying this changes anything about conservation being assumed or derived

>>6397653
conservation of energy in newtonian mechanics, whenever it applies, it's derived from noether's theorem, not assumed.

>>6397613
not really, they are similar in form but they are different statements. The first law in axiomatic thermodynamics can be thought more as a definition of heat. Mechanical energy is not conserved and thus we define the difference as heat.

You cannot talk about conservation of energy in axiomatic thermo because there is absolutely no way to know or define the total energy a priori.

The actual conservation of total energy in a physical theory is a different statement arising from noether's theorem under some (not necessarily true in actuality) assumptions.

>"The 1st Law of Thermodyamics simply states that energy can be neither created nor destroyed"

not exactly, this is conservation of energy, they are different concepts.

>This means that the particles that are building my body are going to exist forever?

no. Particles have energy, they aren't energy.

>>6397572
idgaf
>>6397579
thanks I'm checking it out

>>6397505
Sorry, I used the word measure but regretted it as soon as I sent the comment.

I mean, very practically: if we have a point particle in a higgs-like potential, and we quantize this system canonically, the ground is degenerate and the degenerate eigenspace are invariant under the symmetry.

If instead we consider a quantum field with that potential, we get a single, nondegerate ground, asymmetric and with a particular, but presumably arbitrary v.e.v.; basically there are as many different representations as there are values for the order parameter, and these 'universes' don't communicate.

I understand how this is possible in QM_infinity, Wigner's theorem, Godstone's theorem and shit. But I don't get why it happens, what is the mechanism through which we never observe superposition between different higgs vevs.

For example, I assume you could put (with some difficulty, granted) a quantum magnet in a superposition for magnetization, below the Curie temperature. Is this correct? Why can't we do the same for a field on all spacetime?

>>6397445
I am not being autistic, this is the point. There is no such thing as a white hole. A white hole is just a black hole described with a backwards time coordinate. And you can't traverse a wormhole, you can't get into one horizon and get out of the other.

As to why Schwartzschild black holes connect always to a white hole, that is a black hole 'flipped in time', that's just because the math says so, I guess. I also think, but I should check this, that you could so some kind of coordinate change to make it so that the black-white pair becomes a black-black pair. Meaning that there is no difference.

why do we always measure a single value for the order parameter after SSB, instead of a general superposition? I understand the thing about representations being inequivalent and having different vacua, but I just can't shake the feeling that this is just a restatement of the previous sentence.

>>6397008
they are not one-way. They are zero-way. You can enter from both sides, and you die inside the wormhole. You cannot go through

>>6394350
>In the famous Schrodinger cat experiment the cat behaves like a spin-1/2 particle.

no it doesn't and you have a very active imagination.

>>6395881
>i read somewhere dark energy is what will keep these closed timeline curves open is that bs?

it's exotic matter, not dark energy. Exotic matter is a generic word to refer to some hypothetical kind of matter with the required energy-momentum densities (e.g. negative or monstrously large.) Exotic matter might as well not exist.

Dark energy, instead, is real.

Also, you just need to create the region with CTCs; they can't be destroyed, by definition of destroyed! They are loops in spacetime, they don't evolve in time, and have no end.

What you would need is to keep the wormhole open, but that means getting more and more different ctcs. Wormholes are unstable and not traversable as far as we know.

>is time travel possible in relation to string theory?

ST is also a proposal for quantum gravity, and time travel is discussed in the context of QG, so yes, it's relevant; however please note that the reasoning I made above is based on semiclassical arguments that should apply in general to any theory of quantum gravity. So strings shouldn't be able to make timetravel possible at any scale except around planck scale.

>also what is EFE and FTL

the EFEs are the Einstein Field Equations, they are the equation of motion for spacetime. Spacetime is a dynamical entity which "deforms" as time progresses; influenced also by the energy-momentum content. The EFEs tell spacetime how to evolve given a certain matter content.

global FTL means global faster than light travel, that is, going from one event to another before any light pulse. FTL is easily shown equivalent to time travel, meaning that if you could do one, you can do the other.

>please take it easy on me I'm trying to make the transition to /sci/ and it ain't easy

this place is a shithole, I don't recommend it.