Physics Questions

[Physics Guy No.4894520]

Ok...I'll answer your physics questions, if they aren't too fucking stupid....

Or if anyone wants to discuss physics/physics related shit.

No engineering (I am homophobic!)

[Anonymous No.4894524]

how could we replicate unicorn magic using physics?

[Anonymous No.4894529]

>>4894524
Denying it!

[Anonymous No.4894533]

Why do magnetic monopoles don't exist?

[Anonymous No.4894542]

If light has no mass why does it get trapped in black holes?

[Anonymous No.4894550]

What do you consider a valid/rigorous axiomatization of a) thermodynamics and b) statistical mechanics.

Under which conditions can general relativity be viewed as simply a field theory (of g_\mu\nu) on R^4?
(that spacetime having the topology of R^4 is an obvious restriction)

What is your favorite non-linear sigma model?

[Physics Guy No.4894553]

>>4894542
Why do you assume only things with "mass" get trapped in black-holes?

That is a faulty and shitty assumption.

[Anonymous No.4894554]

Why don't lungs perform as gills?

[Anonymous No.4894563]

What happens if a sun made of lava and a sun made of ice hit each other?

[Anonymous No.4894568]

>>4894553
why is op always such a faggot?

[Anonymous No.4894569]

>>4894550
>Under which conditions can general relativity be viewed as simply a field theory (of g_\mu\nu) on R^4?
troll harder

[Anonymous No.4894571]

>>4894550
>valid/rigorous axiomatization of a) thermodynamics and b) statistical mechanics

Ha. There are none, nor do we need any. Thermo isn't some great "fundemental" physics, it is just shitty approximations ad-nauseum. Some grand axiomatization is not needed or called for.


>non linear sigma

O(3)

[Anonymous No.4894573]

>>4894568
>OP a faggot

Where did OP say he was a engineer?

[Anonymous No.4894574]

Tell me something cool about the Higgs Field.

[Anonymous No.4894575]

Assuming you could somehow travel faster than light, would you be able to see anything behind you? Would see things moving backward in time (since your moving past all of the "older light")? What would you look like to observers (assuming they could watch you in extreme slow-motion)?

[Anonymous No.4894576]

What is time?

[Anonymous No.4894580]

what's going on PHYSICALLY when light hits a media boundary at the Brewster's angle?

[Anonymous No.4894582]

What do you think of this?

http://arxiv.org/abs/1207.4482

[Anonymous No.4894583]

Do you have a gf?

[Anonymous No.4894584]

>>4894550
By field theory do you imply a scalar field theory? Einstein-Fokker just requires Sl(2, C) as a gauge group and the Weyl tensor = 0

[Anonymous No.4894589]

Does it make sense to talk of the density of a black hole?

Does all photon interaction result in a redshift?

[Anonymous No.4894596]

>>4894582

[Anonymous No.4894607]

>>4894596
>typical_theorist.jpg
You seem upset.

[Anonymous No.4894612]

>>4894520

From the POV of a photon, does time both exist and not exist?

[Anonymous No.4894614]

>>4894607
Nope, it's just the way things are. If you think about it, it's a perfectly reasonable thing to do. But they're still going to be mocked for it.

[Anonymous No.4894617]

Has the workload at CERN cooled down at all since the Higgs announcement?

[Anonymous No.4894618]

>>4894612
>implying photons exist

Everything that exists has to have mass.

[Anonymous No.4894619]

>>4894612
Photons (presumably) don't experience qualia, don't have sense organs, and more relevantly don't have rest frames.

[Anonymous No.4894625]

>>4894553

Why do you assume I know jack shit about how black holes work?

What does make light get trapped then?

[Anonymous No.4894632]

>>4894553
maybe because black hole are understood as immense points of gravity and gravity effects things that have mass? this question is perfectly reasonable for an average person

[Anonymous No.4894633]

this is my question: could anybody send me a link where there is a list of all known/discovered elemental particles.

and... if you're so smart than what is consciousness?

[Anonymous No.4894636]

>>4894632
black holes* affects*. ignore my horrible grammar in that post

[Anonymous No.4894639]

>>4894632
Anything with energy-momentum couples to the stress energy tensor. Anything that couples to the stress energy tensor interacts gravitationally. Photons follow null geodesics in Minkowski space and endomorphisms affect them like anything else.

Rest mass is just a quantity of energy that is invariant in all reference frames... it has nothing to do with gravitational effects unless you're talking rest mass from the frame higgs in E8

[Anonymous No.4894644]

>>4894633
http://en.wikipedia.org/wiki/Standard_Model#Particle_content

[Anonymous No.4894650]

troll/10

It's obvious that you're not the real Physics Guy.

[Anonymous No.4894653]

What is your favourite interpretation of QM?

[Anonymous No.4894664]

Please come back based Physics Guy ;_;

You are the hero /sci/ so desperately needs

[Physics Guy No.4894670]

>>4894664
I am not sure if /sci/ is worth saving

[Anonymous No.4894674]

>>4894670
You're really bad at impersonating.

[Anonymous No.4894696]

When do you think we will be able to detect gravitational waves?

[Anonymous No.4894697]

1. What does QM really say about determinism?
2. Is wave/particle duality true for things in general or only for light?

[Anonymous No.4894702]

I have the currents and the times. If I'm trying to calculate capacitance at the formula C = t/Rln(Io/I), what value for R should I use?

I did half of the table, and now coming back to it I can't figure out how I was getting those values.

[Physics Guy No.4894713]

>>4894674
>implying I'm impersonating

Just because I ain't posting all Einstein, doesn't mean it ain't me. I'm on a different computer.

>>4894696
~20 years

>>4894697
Determinism is only possible for a true global system (ie the whole universe). Locally you cannot have determinism.

Wave/particle duality is a neat, but outdated concept. It is only taught to high school students for history sake. No one uses that shitty elementary quantum mechanics anymore, it is proven to be horribly incomplete. Now of days we use quantum field theory.

There is no such thing as particle/wave duality in quantum field theory. The true object is a "quantum field". Depending on how it is observed it will look like a "wave" or a "particle".

Questions?

[Anonymous No.4894719]

>>4894713
You don't know shit about physics and you didn't answer my question.

[Anonymous No.4894726]

>>4894719
Back to /b/, there's absolutely nothing wrong with what he said. He did answer your question.

[Anonymous No.4894730]

>>4894726
No, he didn't. He ignored my question. He didn't even reply to it, because he can't answer a real physics question.

[Anonymous No.4894734]

>>4894730
What queston? Link to it

[Anonymous No.4894741]

please explain magnetism to me. and the best theory as to why magnetic fields exist (on the atomic level). also, why only iron, nickel, and cobalt? is it their orbitals?

apparently all atoms are magnetic. explain this to me. i understand the electron in the orbital probably causes this, so then, once again, why only iron, nickel, and cobalt?

[Physics Guy No.4894744]

>>4894734
If it was a retarded or uninteresting question, then I probably ignored it. See original post.

[Anonymous No.4894764]

Why do particles always follow the path of least action?

[Anonymous No.4894783]

>>4894744
There we go, Mr Troll. Just admit that you're a bad impersonator. Dismissing questions which you can't answer as "retarded or uninteresting" is immature and idiotic. And you don't even put any effort in your trolling. 0/10 for the retarded summerfag attitude of "hurr durr they replied, they so mad, I are epic troal".

[Anonymous No.4894791]

>>4894783
You're the summerfag.

He's been here since the board opened, it's always the same thread topic

Please link to your question as there's many yet unanswered, I'm dying to see how infantile it is.

[Anonymous No.4894793]

>>4894713
Thanks bro.
Considering the shape of the Universe is "flat", does that mean it is not curved into itself, and therefore, if you could travel faster than the universe is expanding, would you reach "the end of space" where you couldn't go on? Also, do we know the size of the whole universe (not just observable)?

[Anonymous No.4894794]

>>4894791
He's not the real physics guy, you fucking retard. How new are you to /sci/?

[Anonymous No.4894803]

Is the total energy of the universe zero?

[Anonymous No.4894806]

>>4894520
What are the main differences between physicists and applied physicists? Like obviously one is more applied (hur) but what areas of study differ the most? Figure there's a lot of overlap

[Anonymous No.4894816]

What OS do you use?

[Physics Guy No.4894820]

>>4894741
>>4894741
The "magnetic field" is a special relativistic effect of the electric field. There is basically one one field the "Electromagnetic field", but depending on how you view it, you will either see it as an electric field, magnetic field, or a combination of both.

All atoms contain moving electrons, each with spin. The movement (apparent movement) and spin each produce a small magnetic moment (think of a magnetic arrow). These arrows can align themselves anti-parallel to cancel any net magnetism, or parrallel to show a net magnetism, or a ton of other crazy senarios!

All materials can be magnetized (at a certain tempertaures that allows for the tiny arrows to move in a parallel configuration) by introducing a external magnetic field. When the field is removed, the arrows realign (relax), this could take seconds or centuries. Permanent magnets are the kind that take centuries for there arrows to relax back into so random configuration.

continued....

[Anonymous No.4894821]

Guys, you can stop asking questions. OP is a bad troll and he's not gonna answer any of them.

[Physics Guy No.4894823]

>>4894820

The common magnets we use (including the ones you mention ) have d-shell (or f-shell in case of rare earth magnets) electrons incompletely filled, hence a net non-zero spin. The configuration of the bulk materials of these atoms is such that it allows for the arrows to move at room temperature (energetically favorable). They then have a huge relaxation time (bulk material property), hence it takes them centuries to loose there magnetism naturally. Now, the question becomes how will these materials align in the external field. Well for the ones you mention it is energetically favored for them to align parallel to the external field (hence they will have a net magnetism). For the rest of the atoms with incomplete orbitals (that have movable arrows at room temperature) they align anti-parrallel.

The determination of the bulk material properties of a substance form first principles in not trivial. It requires alot of material science, chemistry, and quantum mechanics. Often these calculations are so tedious that they do them on super-computers. This is still an area of active research, and there is no easy way to determine all the bulk properties of any random material. We lack the computer power....

Questions???

[Anonymous No.4894827]

How quatum decoherence and entropy are related?

[Physics Guy No.4894837]

>>4894816
>>4894816
It depends which computer I am using, and what I am using it for.

I have windows XP, Vista, 7, Ubuntu, RedHat and SLC5 (Scientific Linux CERN 5), installed on my various computers.

[Physics Guy No.4894839]

>>4894823
Note: it is currently easier (form a vast majority of materials) to just make the material and experimentally figure out its bulk properties, then to try and figure out the bulk properties form theory.

[Anonymous No.4894846]

if i were driving at the speed of light, but then i turned on my headlights, would i be able to see anything?

[Anonymous No.4894848]

>>4894823
>>4894820
>copypasta

[Anonymous No.4894851]

>>4894827
>how does subject - object inversion work?

[Anonymous No.4894854]

>>4894848
>>4894821
>>4894794
>>4894783
>>4894730
>>4894719
Fuck off Carl, I know that's you

[Anonymous No.4894858]

Quantum entanglement happens instantly, regardless of distance. But instantly in relation to what? There is no preferred frame due to special relativity.

[Anonymous No.4894859]

>>4894839
Come on, answer my question, you immature asshole.

[Anonymous No.4894860]

>>4894520
What's wrong scifags? You jelly that engineers do your work plus math and actually apply it to solve problems? No wonder you hate them. It's not like the internet or space exploration was founded by engineers or anything.

[Anonymous No.4894861]

>>4894713
>Determinism is only possible for a true global system (ie the whole universe). Locally you cannot have determinism.

The right answer is simply "standard quantum mechanics is not deterministic; we calculate probabilities." That line about global determinism only makes sense if you're a many-worlder, and one of the main problems with many-worlds is that it's awkward at explaining why the world is observed to obey probabilistic laws.

[Anonymous No.4894866]

>>4894858
If you do the calculations, you'll find nothing observable depends on the frame you use.

[Anonymous No.4894867]

So massive objects curve spacetime, so that objects follow curved paths around larger objects. This explains orbit, but how does it explain gravity that isn't orbit. I'm not moving relative to the earth's surface.

[Anonymous No.4894882]

>>4894867
It's spacetime curvature, and your path extends over time.

[Carl No.4894883]

>>4894854
Hey! Not every quality poaster is me.

[Anonymous No.4894890]

>>4894861
That's frivolous Copenhagen crap. Decoherence is globally deterministic.

[Physics Guy No.4894891]

>>4894861
The term "global determinism" comes across when talking about Bells' inequalities and shit like that. A proof (accepted by the majority of physicist) that quantum mechanics is complete (in form) has existed for a very long time. That there wasn't any missing "local vars" that could eliminate the probabalistic nature. Hence, you could never remove probability on a local level.

This however doesn't say anything about a global level. It could very well be possible that the universe is globally deterministic.

This need not have anything to do with Many-worlds theories.

[Physics Guy No.4894905]

>>4894867
Gravity is pulling you down to ~ the center of the earth, matter is pushing you back up to counteract alot of the gravitational force. Hence, you stay more or less at the same level relative to the ground. But gravity is always there, pushing you down.

[Anonymous No.4894914]

>>4894891
Okay, now it sounds like you're just confused about Bell's theorem. There are at least two reasons to want to add hidden variables to quantum mechanics; one is to explain the appearance randomness without actual randomness, and the other is to explain entanglement without nonlocality. These are two separate issues, and Bell's theorem has everything to do with the latter and nothing to do with the former.

[Anonymous No.4894918]

>>4894867
The metric for any spherical mass is <span class="math">ds^2 = R^{2}(d\theta^2 + sin^{2}\theta d\phi^2)[/spoiler], evolve that with the field equations and you will see how the word lines curve for test particles as they approach closer and closer to the massive object.

[Anonymous No.4894924]

>>4894914
There is no need for hidden variables. With decoherence, the entire universe is in a pure state and evolves globally in a completely deterministic fashion.

[Anonymous No.4894938]

>>4894803
Please respond

[Anonymous No.4894944]

>>4894890
No, it's shut-up-and-calculate crap. Probabilities are the things we compute and compare to experiments. If your interpretation struggles with them, it has a problem.

[Anonymous No.4894962]

I'm an undergrad math major trying to self study and learn as much physics as possible in a short period of time. All the physics I know is some mechanics from the textbook fundamentals of physics by halliday-resnick. How does one study physics properly so that one develops physical intuition and not just algebra skills plugging equations around? What are some recommended textbooks at undergrad level.

[Anonymous No.4894964]

>>4894944
>he thinks the wave function collapses and Schrodinger's cat is real
Please fuck off back to physicsforums

[Anonymous No.4894967]

>>4894803
"Total energy" isn't a very natural concept in general relativity; you can define it, but then the answer is going to depend on how you do so.

[Anonymous No.4894972]

>>4894967
Layman here, what would be some definitions?

[Anonymous No.4894974]

>>4894964
I think histograms of collider events are real.

[Anonymous No.4894975]

>>4894962
http://www.amazon.com/Course-Theoretical-Physics-All-Volumes/lm/RMVH4G2YKW3NH

[Anonymous No.4894979]

>>4894974
That's a horrible comparison and you know it.

[Anonymous No.4894982]

>>4894972
I'm not familiar enough with it for even a half-decent translation into laymanese, but have

http://en.wikipedia.org/wiki/Stress%E2%80%93energy%E2%80%93momentum_pseudotensor

[Anonymous No.4894983]

>>4894803
If you agree with modern quantum field theory, then you agree with vacuum genesis, yes.

If you don't, the only other option is some cyclic model which disagrees with the expansion of the universe

[Anonymous No.4894988]

>>4894979
It's not a comparison at all, it's an example of a probability measured in an experiment.

[Anonymous No.4894992]

>>4894988
Saying a mixed state magically turns back into a pure state and violates entropy is surely more sensible.

Nobody is disagreeing with locally probabilistic measurements. The modern, accepted, non-fringe, shut up and calculate approach to QM is decoherence.

[Anonymous No.4895029]

>>4894992
You can't say things like "globally deterministic" and pretend to be espousing a shut-up-and-calculate interpretation.

[Anonymous No.4895040]

>>4895029
You are hilarious. Decoherence is simply the diagonalization of the density matrix in a preferred basis, with the off-diagonals vanishing at late times.

There is nothing for the universe to entangle with. Please provide a single reference paper that treats the universe as an entangled/mixed system. It is a closed system with no environmental degrees of freedom, and therefore it is in a pure state and evolves deterministically.

Have you even taken undergrad QM?

[Anonymous No.4895055]

>>4895040
lingo is for niggers who are tying to appear more intelligent than they actually are.

[Anonymous No.4895058]

>>4895040
>You are hilarious.
>Have you even taken undergrad QM?
Now you are just trying to rustle my jimmies.

>Please provide a single reference paper that treats the universe ...
I don't think you quite understand what is meant by "shut up and calculate."

>... as an entangled/mixed system.
I'm going to assume the "entangled" part was an oversight on your part, because the universe as an entangled state is what you argue for in the next sentence.

[Anonymous No.4895066]

>>4895055
Lingo? What are you blabbering on about?

If someone claims such disjointed nonsense about QM, they should know QM formalism

[Anonymous No.4895080]

>>4895058
>I'm going to assume the "entangled" part was an oversight on your part, because the universe as an entangled state is what you argue for in the next sentence.
Hahaha, no. Evolution of any quantum pure state is deterministic in the sense that it is given by the Hamiltonian and governed by the unitary operator. As I said before, since there's nothing else for the universe to entangle with, it will remain in a pure state and evolve deterministically for ever if it always was in a pure state. The entire process is unitary.

On the local scale things are very different. When you have a mixed state, there are several possible initial pure states of the system under consideration, and as such irreversibility and nondeterminism.

[Anonymous No.4895079]

>>4894563
if they were made of those materials they would not be stars...

[Anonymous No.4895088]

>>4895058
>I don't think you quite understand what is meant by "shut up and calculate."
By standard definition the universe encompasses everything, lol....

If you assume an entangled state you must assume something more than the universe and disagree with inflation. The initial, standard potential given by inflation is in a pure state.

[Physics Guy No.4895089]

>>4894803
The actual values of shit don't matter, as you can change your measuring system. The only thing that matters are how the values relate to another and there must be consistency naturally.

You could say the universe has a total energy of whatever the fuck you want, the actual number doesn't matter. What matters is the way the energies that comprise the universe relate to another.

Make sense?

[Anonymous No.4895100]

why does annihilation require two particles produced?
Why can't two particles annihilate and then just have a single photon travel in the direction of net momentum after annihilation?

[Anonymous No.4895105]

>>4895080
>since there's nothing else for the universe to entangle with
Okay, I see what you meant now. I didn't understand at first because that's a very vacuous use of the term "not entangled."

> it will remain in a pure state
BTW, entangled states are still pure states; you only get a mixed state if you trace over the degrees of freedom of one part of the system. Which is a sensible thing to do if you want to calculate things, but needs additional justification if your goal is to argue for philosophical statements about the universe.

[Anonymous No.4895111]

>>4895105
correcting myself a bit:
>entangled states are still pure states
*entangled states can still be pure states

The particular entangled states under discussion are pure states, but obviously you can have entangled mixed states as well.

[Physics Guy No.4895113]

>>4895100
You cannot conserve energy and momentum, with only one photon produced. Try the math, it won't work.

[Anonymous No.4895131]

>>4895105
>BTW, entangled states are still pure states; you only get a mixed state if you trace over the degrees of freedom of one part of the system.
It's still a composite system, it just cannot be expressed with tensor products... rather it's linear combination of such tensor products.

It's the same argument, and you still cannot have deterministic evolution either way if it's mixed or entangled, durrrrrr.

>if your goal is to argue for philosophical statements about the universe.
Again, it's in the <span class="math">\mathbf{definition}[/spoiler] of the universe, which consists of EVERYTHING. The density matrix of the universe MUST be in a pure state, unless you're observing a certain part in which you mixed states which appear random. It isn't at all philosophical, lmfao - it's scale invariance of the laws of physics.

Again, I can list dozens of papers on the topic of quantum cosmology as references, my challenge to you would be one which redefines the laws of time evolution in quantum mechanics, and the definition of the universe as encompassing everything in existence.

[Anonymous No.4895140]

I think one direction needs to see this.

[Anonymous No.4895184]

>>4895131
>I can list dozens of papers on the topic of quantum cosmology
Nothing in cosmology is sensitive to interpretations. Your argument is essentially based on extending a particular formulation of quantum mechanics to a domain where it's not clear if it makes much sense.

Simply put, the concept of the universe as globally deterministic but locally random doesn't make a lot of sense unless you're a many-worlder. Otherwise, the random outcomes we observe are part of the universe, so the whole universe should be deterministic too.

>redefines the laws of time evolution in quantum mechanics, and the definition of the universe as encompassing everything in existence.
That should be an "or"; the more sensible approach is obviously the former one. And you've also forgotten the approach of rejecting the notion that the forward-evolving initial quantum state of the universe describes everything that exists. You should know that there are many interpretations of quantum mechanics; many-worlds is just one. There are pilot-wave interpretations, interpretations with final states in addition to the initial one, there's objective collapse theories like GRW; I should even mention consciousness causes collapse for completeness' sake and to troll the people who furiously hate it.

[Anonymous No.4895206]

>>4895184
Meant to say
*Nothing observable in cosmology

[Anonymous No.4895266]

>>4895184
>Your argument is essentially based on extending a particular formulation of quantum mechanics to a domain where it's not clear if it makes much sense.
>Simply put, the concept of the universe as globally deterministic but locally random doesn't make a lot of sense unless you're a many-worlder.

[Anonymous No.4895273]

>>4895184
*so the whole universe should be nondeterministic too.

[Anonymous No.4895284]

Are we going to be able to time travel one day? why/why not

[Anonymous No.4895286]

>>4895184
>Nothing in cosmology is sensitive to interpretations. Your argument is essentially based on extending a particular formulation of quantum mechanics to a domain where it's not clear if it makes much sense.
Where did I ever say the time evolution of a Hamiltonian is subjective?

>Your argument is essentially based on extending a particular formulation of quantum mechanics to a domain where it's not clear if it makes much sense.
Decoherence is quantum mechanics without wave function collapse. Please tell me how a mixed state can somehow turn back into a pure state and not violate entropy. Wave function collapse is 1920's paradoxical crap that has been ruled out empirically.

>That should be an "or"; the more sensible approach is obviously the former one. And you've also forgotten the approach of rejecting the notion that the forward-evolving initial quantum state of the universe describes everything that exists. You should know that there are many interpretations of quantum mechanics; many-worlds is just one. There are pilot-wave interpretations, interpretations with final states in addition to the initial one, there's objective collapse theories like GRW; I should even mention consciousness causes collapse for completeness' sake and to troll the people who furiously hate it.
All of those are philosophical nonsense that involve either hidden variables or entropy-violating wave function collapse, or the vacuous assumption that quantum mechanics is incomplete.

[Anonymous No.4895311]

>>4895266
The universe appears locally probabilistic to us. There is no way for us to escape this probabilistic nature (locally).

However, the more information we have (the bigger system) the less probabilistic things are. Eventually, when we have taken into account the whole universe, we have determinism again.

What part of this do you not understand?

[Anonymous No.4895319]

>>4895311
>However, the more information we have (the bigger system) the less probabilistic things are. Eventually, when we have taken into account the whole universe, we have determinism again.
New guy ITT. This does not currently seem to be true of quantum effects. The "global determinism" interpretations (nonlocal determinism) requires omniscience to recover perfect prediction.

[Anonymous No.4895322]

>>4895319
That's the entire point. Bell's inequalities says no locality/local hidden variables.

[Anonymous No.4895323]

>>4895322
*say

[Anonymous No.4895327]

>>4895322
OK. Sorry, looks like we agree then.

I not sure about that "more info = more predictability" thing. It seems that kind of thing would be experimentally verifiable by now. It might just be "here's the probability distribution from local information, and there's nothing better unless you're God"

[Anonymous No.4895340]

>>4895327
>I not sure about that "more info = more predictability" thing.
DURRRRRR

It's either EVERYTHING IS RANDOM, in which case the DENSITY MATRIX SOMEHOW MAGICALLY FUCKING COLLAPSES and unitary evolution makes no sense (and you get messed up retrocausality effects when you solve for the E-L eqns for a quantum field), or it's globally deterministic and decoherence takes care of the placebo effect of wave function collapse.

[Anonymous No.4895350]

>>4895286
Your /b/-style image macros aren't doing you any favors.

>Decoherence is quantum mechanics without wave function collapse.
That is absolutely not what decoherence means.

>Please tell me how a mixed state can somehow turn back into a pure state and not violate entropy
In Copenhagen with subjective quantum states, mixed states turn into pure states when the observer updates his information about the system. He can't use this in a Maxwell's demon-style fashion to make a perpetual motion device because he would have to forget his measurements. In objective-collapse theories, well, the question isn't even really right because at least in the most obvious ways of doing it, the state is pure the whole time. In fact your whole question seems rather red-herringish.

>Wave function collapse is 1920's paradoxical crap that has been ruled out empirically.
No, it hasn't. (Although I have seen papers claiming it has, but it always turned out the authors fucked up their QM.)

>Where did I ever say the time evolution of a Hamiltonian is subjective?
You didn't. Where did that come from?

>All of those are philosophical nonsense that involve either hidden variables or entropy-violating wave function collapse, or the vacuous assumption that quantum mechanics is incomplete.
Ah, but the assumption that quantum mechanics is complete is also "philosophical nonsense."

[Anonymous No.4895386]

>>4895350
>That is absolutely not what decoherence means.
QM without collapse = decoherence is the only way to recover observational effects. Collapse is an added effect to the dynamics of the system. Using the stock Schrodinger/Heisenberg formulation = normal dynamics of quantum mechanics, and decoherence is a side effect -> http://arxiv.org/abs/quant-ph/9803052

>In Copenhagen with subjective quantum states, mixed states turn into pure states when the observer updates his information about the system. He can't use this in a Maxwell's demon-style fashion to make a perpetual motion device because he would have to forget his measurements. In objective-collapse theories, well, the question isn't even really right because at least in the most obvious ways of doing it, the state is pure the whole time. In fact your whole question seems rather red-herringish.
Nope 0/100 -> http://en.wikipedia.org/wiki/Entropy_(arrow_of_time)#Cosmology


>Ah, but the assumption that quantum mechanics is complete is also "philosophical nonsense."
0/100 back to >>>/physicsforums/

[Anonymous No.4895388]

>>4895311
What is this, advocacy of some hidden variable theory? You'll have to explain which one you're talking about then, because standard quantum mechanics says nothing resembling what you describe.

[TraDrac !!oOBd7ADelbg No.4895392]

what is a black hole? could a black hole explode in some way that we know of? do we have solid evidence that one couldn't explode?

[Anonymous No.4895408]

>>4895388
Not that guy, but no, it's the opposite of hidden variables and is standard QM with decoherence.

Please read other posts before making a fool of yourself

[Anonymous No.4895412]

>>4895340
That's not what I'm talking about. I'm questioning whether knowing half of the universe's state vector gets you any more predictability for quantum phenomena than just the local information. Is getting predictability out of quantum phenomena an all-or-nothing question of "do I know the entire state vector"?

[Anonymous No.4895418]

>>4894553
I love Oprah Winfrey.

[Anonymous No.4895419]

>>4895412
If you knew the entire universes state vector, you would know the evolution of the entire universe as you would have a PURE STATE. There wouldn't be ANY entanglement/superposition and thus you would NOT have any probabilistic outcomes!

What is so difficult to understand?

[Anonymous No.4895423]

>>4895386
>http://arxiv.org/abs/quant-ph/9803052
Thus, the result of this interaction is a density matrix which seems to describe
an ensemble of different outcomes n with the respective probabilities. One must
be careful in analyzing its interpretation, however. This density matrix only
corresponds to an apparent ensemble, not a genuine ensemble of quantum states.
What can safely be stated is the fact, that interference terms (non-diagonal
elements) are gone, hence the coherence present in the initial system state in (3)
can no longer be observed. Is coherence really “destroyed”? Certainly not. The
right-hand side of (3) still displays a superposition of different n. The coherence
is only delocalised into the larger system. As is well known, any interpretation of
a superposition as an ensemble of components can be disproved experimentally
by creating interference effects. The same is true for the situation described in
(3). For example, the evolution could in principle be reversed. Needless to say
that such a reversal is experimentally extremely difficult, but the interpretation
and consistency of a physical theory must not depend on our present technical
abilities. Nevertheless, one often finds explicit or implicit statements to the effect
that the above processes are equivalent to the collapse of the wave function (or
even solve the measurement problem). Such statements are certainly unfounded.
What can safely be said, is that coherence between the subspaces of the Hilbert
space spanned by |n> can no longer be observed at the considered system, if the
process described by (3) is practically irreversible.

I don't disagree with any of this. In fact, it disagrees with your position that decoherence obviates the need for wavefunction collapse or alternate solutions to the measurement problem.

[Anonymous No.4895443]

>>4895423
Okay then have fun with your hidden variables/wave function collapse/infinite parallel universes

[Anonymous No.4895450]

>>4895419
That gives you many-worlds, and it has its own problems -- namely that you can't just get by with just the state vector as some adherents like to think; you need some prescription for calculating the subjective probability to find yourself in a particular world, which is often tacked on in a rather ad hoc fashion.

Or do you think somehow that if you started with the universe in an pure state, and evolved it forward unitarily, you would somehow not get the cosmos of many-worlds? (Because in that case, you're not taking a philosophically troublesome position; you're flat-out wrong.)

So are you advocating many-worlds or not?

[Anonymous No.4895453]

>>4895443
I actually like final states, but I have the honesty to admit it's philosophy not science.

[Anonymous No.4895456]

>>4895450
Why do you think many-worlds has anything to do with this? There is no parallel universes or branching of mixed states.

The inflationary potential is A PURE STATE. The universe evolves based on this irrelevant of any philosophical nuances.

[Anonymous No.4895481]

>this thread
>Bohmian mechanics

[Anonymous No.4895482]

>>4895456
Looking at states of the inflaton fields is probably not the best illustration of differences between interpretations, so let's imagine a universe created last Thursday consisting of only a room with Schrodinger's cat and an experimenter. Under unitary evolution of the wavefunction, we wind up with a PURE STATE composed of a live-cat, happy-experimenter component, and a dead-cat, sad-experimenter component. This PURE STATE is the kind of universe envisioned by many-worlders. Decoherence makes it extraordinarily difficult (but not in principle impossible) for the experimenter from carrying out an experiment demonstrating interference between the live-cat and dead-cat components of the state.

What do you think happens in this scenario?

[Anonymous No.4895487]

>>4895482
>uses entanglement to get out of it
>implying the universe started in an entangled state
0/100

[Anonymous No.4895489]

can you please direct me to where i can get the proof that the electric field inside a hollow conducting sphere is zero even if a test charge is placed inside the sphere off center? i know it has to do with using a cone and hard angles to derive the proof but im a freshman and my text book lacks answers.

[Anonymous No.4895504]

>>4895489
Maybe I'm misinterpreting you, but I'm pretty sure that isn't true. Could you draw a picture of your setup including an indication of where you're saying the field is zero?

[Anonymous No.4895518]

>>4895423
What explains the EPR paradox then if decoherence isn't responsible for wave function collapse

[Anonymous No.4895525]

>>4895504

Sorry, I meant hollow insulating sphere. But the example is question is at:

http://youtu.be/Hlj5vGOSQlY

At 38:00

I learned this in class and my professor didn't give a proof for his reasoning. When I tried to search online for info, that was the best thing I could find.

[Anonymous No.4895539]

>>4895518
Not sure what you think the paradox is. Quantum mechanics predicts the same results in any reference frame. It doesn't matter who measures first. You can't explain the results using a local theory like Einstein and his coauthors wanted to, but quantum mechanics isn't local in that sense.

[Anonymous No.4895556]

>>4895525
Oh, sorry, for some reason I missed the word "test" before charge in your post, and I was thinking about the field the charge would make inside the sphere.

You can use either Gauss's law or the argument he describes in that video. Gauss's law is more general and powerful. Have you tried reading about Gauss's law?

BTW, for a conducting sphere, it follows from the fact that the inner surface has the same electrical potential everywhere, so it doesn't even need to be a sphere.

[Anonymous No.4895569]

>>4895518
There is nothing else if you don't want to violate local causality.

[Anonymous No.4895584]

Why do certain stars have different lifespan? Not time they live but once they die out from what I know they can become three things. White dwarf nuetral star or black hole. What causes this? Theories on what happens one absolute zero es reached. 2012 maybe?

[Anonymous No.4895638]

>>4895556
Oh that makes things a lot more clear. I thought he meant the the cone/hard angle proof was the only proof for an off center charge.

[Anonymous No.4895661]

>>4895638
Yeah, what he's showing is the hard way. That way you get to appreciate how much easier Gauss's law makes things.

[Anonymous No.4897382]

You're saying, it seems, that the universe as a whole is entangled since the big bang?

[Anonymous No.4897458]

>>4895584

What stars become when they 'die' is entirely related to their mass and initial chemical composition.

After shedding much of their mass after much stellar evolution, stars that have 'cores' >~2 solar masses will collapse into black holes...

Otherwise, they will remain white dwarfs (if under ~1.4 solar masses) and eventually cool. Otherwise, they are considered neutron stars

[Anonymous No.4897590]

What's the metric for a particle in a uniform gravitational field?