/sci/ - Science & Math

If a tree falls on a woman, what sound does it make?

What, exactly, is the reason why we can't simply combine the two (QM and Relativity, I mean)? I've never understood.

Feel free to explain mathematically, if you want.

>>1979926
Sweet silence afterwords, that much I know. No more nagging about how she FEELS something is correct, or wrong.

so wussalldafuss is about

Those are the things I'll be studying when I finally enter University. Are they the most interesting topics like I think they are?

Does the Copenhagen Interpretation really suggest that there can simultaneously be a superposition of logically contradictory states?

i.e. Schrodinger's cat -actually being- "dead and not-dead" thereby violating the logical law of the excluded middle.

Or is this just a layman's mistake?

What was wrong with the Klein-Gordon equation?

>>1979931
Nope. This question is fallacy, trees don't grow in kitchens.

I've been told that Schroedinger's Cat is a thought experiment meant to show that quantum mechanics is inherently flawed and really shouldn't be used to describe the idea of superposition. Is this true?

>>1979956
Yes it was originally created to show the absurdity of the Copenhagen interpretation.

OP here
>>1979928
Many Reasons. Don't know where to start.
One big problem: In GR you have curved spacetime. In general the Einstein Equations allow crazy solutions, especially in general you don't have all the symmetries you have in flate Minkowski space. You can search for "Maximally Symmetric Spaces".
Then, if you don't have time translation symmetry you have probems to define a Hamiltonian (Energy Operator) and so you don't know how to rigourously define the time developement of fields (if you want to use fields)

I can go on if you demand with other examples what fails but I also look to answer different questions.

>>1979962
Where is the absurdity? The wave function collapse? Assuming something on a macro scale can be in superposition?

>>1979936
"logically contradictory states" is not a nice frase I would say. Look up "Quantum Logic" on wikipedia.
The answer to your question is yes, I guess. But in QM you should not take events between measurements too serious. You shouldn't in general imho.

>>1979956

Being that QM doesn't apply on the macroscopic scale, the thought experiment wasn't of much use.

OP here 3

>>1979937
define "wrong". It describes Bosons (even spin) so you can't use it to describe electrons, if thats your problem. Also, a classical answer would be you can only define "flawed particle densities". has to to with it beeing second order in time derivatives

>>1979956
The experiments true value is actually to show, that microscopic events can have macroscopic consequences. nothing wrong with the cat though experiment

>>1979990
Really? I heard they were going to cool down a tardigrade to almost absolute zero to see if the creature can be in superposition.
http://xenophilius.wordpress.com/2009/09/27/schrodingers-tardigrade-may-be-first-life-form-to-prove-
multiple-universe-theory/

>>1979920
How could you explain Erik Verlinde's entropic gravity theory in 4chan terms?

>>1979920
How does one observe the path of particles in the double slit experiment? What is the method and apparatus used?

I'll give one raven_orgasm.jpg (work-safe) to you if you answer my question.

>a guy who understands Quantum Field Theory
>a guy who doesn't know what he's talking about

explain Schrödinger's cat in detail, but in terms someone who only knows up to first year a level physics

>>1980014
Was that a Feynman reference?!
Please tell me it was!

OP here 4

>>1980009

I'm not really good with experiments ect. but your question is kind of confusing actually (unless its a joke). The point is that you don't observe the path. There is no path.
Troll, or did you mean something else?

>>1980008

I just scimmed the paper, but the answer depends on how much you know about the physical entropy.
Like many theories now (theories I like), it tries to explain gravity as secondary product of entropic dynamics, if you will.
As far as I understand you don't really use equations like the Einstein equations, but you take some rules how things should develope and go step by step (in a Wolfram kind of way)

But I don't know much about entropy-gravity, see topic

I'm going to assume you know a lot about supersymmetry...
What is the name or description of the animation where they take a bunch of particles from the standard model and line them up on a grid according to their charge and spin, in a hexagonal way. Then they 'rotate' the picture through a bunch of dimensions and you see the symmetry of every particle expand, and with holes being generated for where the higgs and it's symmetric particle goes?

I hope I'm not babbling. It resembles pic, but not quite.

OP here 5

>>1980014

I know the problematics concerning the claim to understand QFT. What I ment is that I can answer the questions here without talking bullshit.

>>1980020
I think I can't/won't explain something in detail, I rather want to answer questions.
What do you know about it - tell me and I tell you what is missing.

>>1980006
>/x/ site
>experiment actually involves viruses
>tardigrade only mentioned tangentially
>flat-out lies about macroscopic superposition being established fact in QM
>experiment never performed

Yes, really.

Quantum suicide, yes? No?

>>1980074
that the guy put a cat in a box with some radioactive thing which may or may not break depending on interaction with some subatomic particle and that the cat is both alive and dead while in the box.

What I don't get is how this links in with the copenhagen interpretation and how this was meant to make quantum physics look daft.

For all I know that all could be wrong though, i'm going off memory.

OP here 6

>>1980058

I don't know much about supersymmetry (I know a bit)
I don't know what "animation" you mean but the grids a rather a invention by mathematicans. It's used in classification of Lie Groups (and their Lie Algebras).
You may find out more about these pictures if you look up Lie Group/Algebra Representation Theory (if you are a mathematican of a physican.
Or "Gell-Mann", the man who brought them into physics in the 70's.

It would help if I knew on which level the questions are to be answered.

>>1979936

One day I will have explained this enough that Schrodinger's Cat will be dead as a meme: It is not observation alone which causes waveforms to collapse. Any interaction does (scientific observation being just another type of interaction). Cats feet interact with box, cat's lungs interact with air, cat's molecules interact with one another. Therefore there is no superposition, therefore cat is either alive or dead not both.

mind giving a brief summary of van der walls forces to a chemist?

>>1980020
Well hell, I can do that.

Schrödinger came up with the cat in the box thing not to explain anything to his peers, but instead to show to the general public that quantum mechanics as it is and was is fundamentally different from the macroscopic world people are use to. In the macroscopic world, things happen regardless of whether or not something or someone is around to witness it. In the quantum world, nothing happens until there is a "witness". That isn't to say that a conscious observer is needed for something on the quantum scale to happen (a lot of philosophical nut jobs try and argue that). An observer can be anything including another particle. It's as if the collision of two particles is not predetermined, it simply happens if and when it happens. Before the actual collision any number of paths were possible. This indeterminacy still exists with molecules too. Two molecules colliding have the same indeterminacy. However, as you scale up, including more and more particles, the distribution of the possible paths the colliding molecules can take (also known as the wave function) shrinks. Because the macroscopic world involves so many particles there is practically no possibility of a baseball deviating from its predicted course to any great degree.

So, on a quantum scale, the cat is both alive and dead until it is "observed" the same way colliding particles are can be taking any number of paths until they actually collide. Keep in mind though that an actual cat in a box involves a LOT of particles, so there is relatively no indeterminacy, just in case you were under the assumption that the cat in the box experiment was a real experiment. It, as I said, was simply created to show the contrast between the quantum world and the macroscopic world as people see it.

>>1980107
If any interaction caused state vector reduction, there would be no entangled states. Since entangled states have been observed, your solution to the measurement problem is wrong.

>>1980136
>If any interaction caused state vector reduction, there would be no entangled states.

And what exactly are you basing this conjecture on?

OP here 7

>>1980104

The experiment should show, that if you are consequent with this superposition of the wavefunction thing with particles and you then couple the wavefunction to a cat (a macroscopic object), then the cat has the same superposition going on - which is strange. If you believe in the copenhagen interpretation for particles, then it's alo true for everything you don't observe atm (is the moon there if you look away?)

practially speaking
>>1980107
has a point. you can't quite realize nonobservation of macroscopic objects. But that doesn't proove QM wrong, just counterintuitive (if you come from the classical mechanics side)

-------------


No QFT and GR question?

>>1980151
Do you know what an entangled state is?

>>1980052
>I'm not really good with experiments ect. but your question is kind of confusing actually (unless its a joke). The point is that you don't observe the path. There is no path.
Troll, or did you mean something else?

In the double slit experiment, particles display their own wave function beyond the two slits in the form of a series of bright lines on the surface they are impacting. However, if one "watches" which slit the particles take the wave function collapses and the particles go through in straight lines, creating two intensity peaks instead of many.

I did the experiment in Physics for Scientists and Engineers III, Sophmore year. Surely you must have done the experiment yourself in class.

I never really asked my professor HOW one goes about telling which slit particles enter, and my preliminary searches online didn't turn up much. I was hoping you might know what I am talking about.

In my physics classes I am always half afraid my questions are stupid (a problem I don't have in any other classes besides mathematics). I hope that isn't the case now. :(

>But I don't know much about entropy-gravity, see topic
>Implying Quantum Field Theory and General Relativity doesn't have anything to do with Entropic gravity theory.

>>1980152
What questions are you expecting?
Perhaps people don't know enough to even ask questions which is why you're getting all of those cat questions.

OP 8

>>1980116

ya, sorry but I don't want to make that a general physics thread ;_;

>>1980162

Yes, and your presumption is senseless.

>>1980175
Can you write down a Hamiltonian that produces an entangled state from a non-entangled state?

>>1980106
Oh sorry, physics undergrad here, saw a talk where the presenter explained exactly where the higgs came from, but can't remember who it was or where I saw it.

Looking up what you mentioned as we speak, thanks.

Do you think "electroweak unification" is a misleading name?

OP 9

>>1980168

If you have multiple slits, and you just wait for the result and don't look where the particle went - then you can't tell. The particle is not a particle while propagating but "a wave". It didn't take a specific slit.

>>1980171

ya kinda. entropic qravity is quite different from standard model QFTs. "nothing to do with" is of course never true.

>>1980172

you are right. but lets see whats happening next.

i puts cheezburgur in box wif cat
cheezburger is eaten and not eaten at sames tiem
???
SCEINCE!!!!!!!

OP 10

>>1980214

hehe, intersting question. but, no. Why?

I think "General Relativity" is of course a not very good name. At least Wheeler "Geometrodynamics" would have been a better name.

>>1980236
Because at high energies, you still have two gauge fields.

>>1980182
The point here being that said Hamiltonian is an interaction between two systems. And it does not cause state vector reduction.

OP 11

>>1980247

Well they are the children of a single gauge group and you have a single lagrangian, so I think it's a good name.
Arguing your way, you could even say that you have four gauge degrees of freedom (3 plus 1)

>>1980213
>If you have multiple slits, and you just wait for the result and don't look where the particle went - then you can't tell. The particle is not a particle while propagating but "a wave". It didn't take a specific slit.
The double slit experiment is so prominent in early quantum mechanics education because: (1) it gives students a tangible example of a wave function and (2) it shows students that a wave function collapses when observed. You already said you aren't much of an experimentalist so maybe you just forgot about this lab.

This link that explains the double slit experiment very generally. It might jog your memory as to what I am talking about.
http://www.fen.bilkent.edu.tr/~yalabik/applets/collapse.html

>>1980119
Thank you.

OP 12

>>1980264

I don't understand what you are implying. I forgot the lab? Don't you agree with my statement, then explain what the problem seems to be.

>>1980262
What do you mean by "children of a single gauge group"?

There are two independent coupling constants. In order to have grand unification, we still have to get all three (not two) coupling constants to come together at some renormalization scale.

Of course there's a single Lagrangian, but under that counting scheme, all three gauge fields are already "unified" in the Standard Model. Even gravity is "unified" with the rest of them provided you're willing to accept a low-energy effective field theory.

>>1980291
One can detect electrons passing through a slit. When one detects the electrons moving through one slit the entire wave function collapses, see link.

My question is - What method and apparatus is typically used to detect the electrons (or whatever particles one choses to use) passing through the slit?

>>1980340
>One can detect electrons passing through a slit.
Not OP, but I've never heard of that part actually being done. I think you're confusing a thought experiment with a real one.

>>1980330

meaning the abelian elctromagnetic U(1) part just factors from the SU2.

>provided you're willing to accept a low-energy effective field theory.
>implying there exists a fundamental QFT and quantum field physicists shouldn't just take what works for their area of research

well, I don't want just the low energy limit, thats kinda boring. But I don't see why a QFT unification should work at all.
Still, I don't have a problem with the name - there are no contradictions and you can learn it as a single theory.

>>1980340
ahh, you mean "if one decides to interrupt the propagation, how does one do it?"
In this case, sorry I dont know ^^ you guessed it.

>>1980383
The electromagnetic U(1) is a combination of a component of the Standard Model SU(2) ("isospin") and of the Standard Model U(1) ("hypercharge"). It doesn't come just from SU(2) as "unification" would imply it did.

OP 14

>>1980425

No, it doesn't come from SU(2) of course. The parent gruop I was talking about is a 4-dimensional group:
SU2 cross U1. The Fields are W^1,W^2,W^3,W^4 or whatever.

Then a U1 subgroup factors out (but not the same U1 as above, hence the mixing) and leaves a SU2 behing (again, not the SU2 above). The SU2 is broken.
The nexw mixed fields are then named A, W^+/-,Z^0
Now you have the electric U1, which is an practical gauge freedom. The charges are a wild combination but the group befor the symmetry break is a nice (reducible) Lie Gruop, hence unification.

Suppose we have a vacuum spacetime and the Weyl spinor <span class="math"> \Psi_{ABCD} [/spoiler] is algebraically special with n-fold principal spinor <span class="math"> o [/spoiler] (n = 2,3,4) and the space time is flat (or <span class="math"> o [/spoiler] generates a geodesic shearfree congruence)
then czn you say how we arrive at the following result?
<div class="math"> \nabla^{AA'} \Psi_{ABCD} </div>
contraced with (5-n) <span class="math">o[/spoiler]'s vanishes.

Question:
When and where do physicists learn about groups?
And how much of algebra do you tend to learn?

OP 15

>>1980502
>mfw you own the shit out of me with a question on a topic, which I'd be glad to know more about.

I like me some bundles, but I'm just trying to understand the cartan approach to gravity, i.e. frames and so on.

>>1980550

damn. i just picked one of the questions off the last problem set for my course, hoping i could pikey an answer.

i have no idea what the question is asking yet, start on spinors next week i think.

>>1980550
Alessandra Torresani is so cute in that photo :3

OP 16

>>1980547

The problem is, imho, that we get introduced to groups via Lie Gruops.
Since most of the physicists, I'd say 80%, go into experimental physics, you only hear of the existance of finite groups maybe in relation with cristals. But condenced matter physicist on average don't even understand the fourier transform properly.
So you have to learn, say the concept of Normal Subgroups on your own.
To answer your question, I'd say you get to know some (Lie) Groups in the defining sense about 5 to 7 semesters in. (Lorentz group in GR for example)

>>1980570

upload the question set (just out of couriosity)

>start on spinors next week
what do you know now about them, i.e. how much already?

>>1980592
That makes sense. I was wondering cause I'm a math master's and some of the physicists are all like "pfft...algebra, take your pure stuff and cram it."
And also 'cause there aren't many (any?) physicists in my differential topology class when you would think it should be some of the theoretical physicists prime concern.

>>1980592
sorry, we only get given the problems in hard copy (lecturer is a bit old school) i can type up a few if you really want?

I've noticed a few of them are questions taken from Stewart: advanced GR, and Misner etc.: gravitation (obv) if you have a copy of either?
the stewart book has no worked answers unfortunately.

As for what I know about spinors: not a lot.
I'm only learning about QFT now, and the GR course has no prerequisites for anything quantum sothe spinor stuff is built up independently, from an abstract way.

we've just finished stuff on simplectic structures.

How does it feel being the biggest fag in the world?


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(")_(") This bunny, copy and past for WORLD DOMINATION

"If you stare long enough into the abyss the abyss stares back at you"
-Baulder's Gate

>>1980630
oh, and i should point out. i'm a mathematics grad not a physicist so there's a few things i maybe should know that i don't yet.

OP 17

>>1980579

Go watch "Malcolm In The Middle - 5x04 - Thanksgiving"
I fell in love back in 2003 and then expected never to see anything of that girl on TV ever again.

>>1980613

As I said, 90% of them never need it. They kinda fear it. They don't want it and I can't blame them.
In mathematics you learn about Residues in the...6 semester? In physics, you need to use it in the third.
Also, the math education enables you to go into statistics ect. but in physics, you don't really ever need discere maths, the galois theory, logic (hehe), set theory ect.
Since more or less everything is Cînfinity in physics...you only need differential topology if dive deep into yang mills theory ect., which in mathematics goes under "Index Theorems", "Chern Classes" and such.

>>1980630
>simplectic structures
?

Anyway, I probably will not be able to help with your problems. If you have any question you think I can answer - you're welcome

OP brb

OP I have a question.

What prevents a large system of particles (say a cloud of electrons) in synchronous oscillation, and without external interference, from attaining a superposition together thus bringing quantum maddness into the macroscopic world.

Why is the chance of something happening the same as something happening in quantum mechanics?

How can you say that something is both happening and not happening, no matter how small the scale, if there's simply a CHANCE of two things happening (one or the other)?

That sounds dumb to me. That's just taking probability as occurrence.

>>1980633
It's originally Nietzsche.

Why is Black Black and not Purple

>>1979920
anon can you know suck cock better with your knowledge than before?

>>1982481
the OP never said he was an engineer? did he?

OP re

>>1981121
I can't answer your question, but there are currently with "Fullerene", see wikipedia, where you can see quantum effects on pretty big (macroscopic?) objects

>>1982522
currently experiments*

i don't know anything about topo and manifold

i do know some theories about group rings field

i finished linear algebra course

i finished apostol -advanced calculus

is that enough for physic

i guess that op must be a math loving azn
showing of he is also good at theoretical
physic troll

this happed to all azn geeks who think they are
fucking superior

pathetic little cunt

>>1982684
theory is confirmed

>>1979920
explain this

This is dull. Dubs get, this turns into a thread about /sci/'s Utopia land its gonna get.