The h Bar

1:32 AM

← did anyone like blade runner as much as me? fell in luv with joi the replicant, ana de armas o_O <3 — From Cuba with love: New Bond girl Ana De Armas's epic rags to riches rise that saw her escape poverty in Havana to star alongside Daniel Craig in the upcoming 007 blockbuster dailymail.co.uk/news/article-7045063/…

skullpetrol

2:14 AM

@NovaliumCompany sounds like you should talk to a career guidance counsellor.

\o @heather

skullpetrol

2:48 AM

heather

3:20 AM

o/

Sir Cumference

3:37 AM

@RyanUnger Oh btw what happened to your 0celo username?

Abhas Kumar Sinha

4:19 AM

@vzn I've worked as a Lead Developer and Lead Designer at Zackquarks Studio. I've also been very active in Godot Community, helping others.

@vzn Here's an Official Link to the renderer: mitsuba-renderer.org I mainly worked for Photorealism and abstract/Modern Art. My most of the work are based on Nature Scenes. But, also be careful, Mitsuba is not a real-time renderer, hence, can't be integrated to Godot. You can use it with Blender. It works well with blender.

@skullpetrol The sentence that's quoted, is logically very incorrect. If you say 'dont believe them' then following the meme, no one would believe your meme, because it says not to believe those, but if you don't believe it, then, then, you'd believe other memes which have a photo and quote against that. So, that's not a correct way to make meme.

There's a curse Book, I've seen on Amazon, people say that those who read that book, die. Anyone interested to read that to me? XD

skullpetrol

7:17 AM

@AbhasKumarSinha i agree

365 days later...

Abhas Kumar Sinha

7:41 AM

@skullpetrol Happy new year XD

skullpetrol

8:20 AM

:D

PM 2Ring

8:44 AM

Also see thoughtco.com/the-problem-with-quotes-on-the-internet-3970560

skillpatrol

8:59 AM

John Rennie

@skillpatrol groan :-)

skullpetrol

:-)

Physics Meta

11:06 AM

0

Q: Was the Chixculub asteroid impact really the main cause of dinosaur extinction?

The world-wide forest fire claim doesn't stand up to examination;many forests survived the impact & so did many creatures far more fragile than dinosaurs. Climate change caused mainly by the Deccan Traps supervolcano seems a more likely main cause,so have proponents of the asteroid theory wildly ...

discussion

Novalium Company

12:04 PM

I'm reading Q is for Quantum and I'm having hard time understanding the entanglement part. I don't know if someone has read it but in the book the entanglement relies on the two balls interacting before the experiment and then somehow instead of WW, WB, BW, BB they both have WW, WB, BW. The part where BB state magically disappears is a bit confusing. I mean, this doesn't tell me anything about them communicating in some nonlocal way.

knzhou

^ Well, if you don't see any nonlocal communication going on, it's because there really isn't any.

It doesn't look like what you heard in pop science, but that's because pop science was wrong.

Novalium Company

Finally some significant difference between pop-sci and what actually happens.

I mean, I expected some states changing instantaneously, magically sending information to the other ball and so on. But all I learned is that in the entanglement process both balls lost a possible state.

Entanglement is more messed up than I thought :P

"When we observe a state of a ball in one location, the outcome of that observation can depend on what's happening to another ball in a different location". Actually I didn't notice any communication between the balls in the telepathic experiment described in the book.

It's much simpler: When the coin is heads, the ball has WW, WB, BW since it doesn't go through the PETE box. When the coin is tales, the ball has WW, WW, WW, WB, BW, -BB. I don't see any communication between the balls.

oh wait

I think I get what's the dependence between the two balls.

I'm stupid

If one of the two people put their misty ball in a PETE box, the misty possibilities change for the other person's ball. Is that the communication?

ACuriousMind

12:28 PM

There is no communication.

Novalium Company

But the possible outcomes of the ball change due to the other ball going through a PETE box.

Something must tell the ball that the other has went through a PETE box :P?

How can it be predetermined whether the person will put the ball through the PETE box or not.

In the book the balls get entangled so they can be in these misty states WW, WB, BW but no BB. Does that mean that if we observe one of the balls to be black, we know for sure the other is white.

ACuriousMind

@NovaliumCompany Yes

Novalium Company

That's the "communication"?

ACuriousMind

I repeat, there is no communication. That the other ball is white if the one we looked at is black is just a fact.

user2723984

@NovaliumCompany there is no communication, you know the ball on the other side is white but the person on the other end doesn't and won't know it unless they measure or you tell them using classical communication

ACuriousMind

12:37 PM

There is 0% probability even before we look at any ball that both balls are black. So we won't observe two black balls. You don't need communication for that.

Novalium Company

Yep. Then what is the entanglement part?

ACuriousMind

You only need to believe that there is communication if you stick to the classical idea that you can assign definite states to the individual balls. But in an entangled state, you cannot do that - there is no individual state of either ball, there is just the total state of both balls together.

Novalium Company

The entanglement part is when one of the balls is put through the PETE box, where the PETE box immidietly changes the possible outcomes of the other ball?

ACuriousMind

@NovaliumCompany You'll have to explain in a bit more detail how the book sets up this scene

But, in general, "entanglement" only means that you have a state of a system in which you cannot assign definite states to the subsystems. In this case, it means that the WW + WB + BW state of both balls together does not allow us to assign states to the individual balls that would match the outcomes of the WW + WB + BW state.

Novalium Company

The two balls are entangled so the possible outcomes are WW, WB, BW (W white, B black) where BB is not an allowed state in which the balls can be in. When one of the balls is put through a PETE box (50% chance to be white, 50% to be black) the outcomes become WW, WB, BB, WW. (that is when one of the ball is put through PETE and the other isn't). If both balls are passed through PETE, the outcomes become WW, WW, WW, WB, BW, -BB.

@ACuriousMind It doesn't make sense for a single ball to have WW, WB, BW states :D

ACuriousMind

12:47 PM

@NovaliumCompany What I mean is that for two balls with outcomes WW, BW, WB, BB, you can explain that by saying that each of the balls is individually in the W+B state you get when passing a white ball through a PETE box. You can't find such individual states for the WW. BW. WB outcomes.

Novalium Company

1:02 PM

You mean each ball has superposition possibilities? :D Like misty in a misty?

Simply said, we cannot talked about a single ball's possibility in entanglement situations?

ACuriousMind

Yeah, like that

Novalium Company

1:32 PM

Cool

I really hope I'm understanding the things properly this time, but it's never too late to reread the book.

Ryan Unger

2:37 PM

@bolbteppa ??

@SirCumference idk, it's still there for me

@ACuriousMind steam summer sale isn't for over a month D:

vzn

@RyanUnger have you seen the Ludyk book? maybe regarded as some kind of inside joke among hardcore GR theorists?

Ryan Unger

3:12 PM

@vzn It's an unknown book

I showed it to @Slereah years ago

Novalium Company

3:47 PM

Every rule has an exception, so what's so weird about quantum entanglement being faster than light? :D

ACuriousMind

4:03 PM

It's...not faster than light in any meaningful sense. The no communication theorem guarantees that entanglement does not transmit information.

vzn

@NovaliumCompany glad you are discovering the joy + mystery of QM. keep in mind even the experts dont really have definitive answers to some of the deep questions it raises. try finding/ reading the famous quotes by bohr echoed by feynman about QM being shocking/ incomprehensible... there are some other new ideas "emerging" very worthwhile to look into...

@RyanUnger published by springer. they typically have (sometimes very) high editorial standards, but sometimes edgy or cutting edge material...

Sir Cumference

@RyanUnger why can't ya give me a straight response....

Slereah

He is cursed to speak in riddles

vzn

4:28 PM

@Slereah why not check it out Mr GR? might find something new! how about review it on your blog? promise to comment if you do... caveat may end up citing Tenev + Horstemeyer :)

Slereah

@vzn It's all very basic GR

Novalium Company

@ACuriousMind Cool. I'll take a look at that theorem. I thought they "send information" between each other but I'm happy I'm getting to the point of distinguishing pop-sci BS QM from the real QM.

vzn

@Slereah have you actually looked at it? or maybe just the ToC on amazon? :|

Slereah

I looked at the ToC yeah

It's your basic math intro + Schwarzschild solution book

vzn

@Slereah huh. maybe you might want to look at the math too... o_O

Slereah

4:34 PM

Not too dissimilar to Callahan

vzn

@Slereah Callahan does it without tensors?

Slereah

Fairly basic tensor stuff

vzn

basic!

> After completion of the book, I discovered the paper [37], where Einstein's equations of a similar shape are derived.

[37] → ?

Ryan Unger

4:53 PM

not using tensors is brainlet stuff

that's first semester algebra

Novalium Company

@RyanUnger Are you Blue?

danielunderwood

What exactly is GR without tensors? Just choosing a coordinate system and working with components all the time? That's what my GR course did and I went slightly crazy trying to figure out what exactly a real tensor was...though it didn't help that I kept looking for physics/engineering explanations rather than just looking up a math definition

Secret

5:14 PM

Made up model: Time fluid paradigm:

Picture time as a fluid, described by the continuity equation

Now consider a volume of space which said fluid can be "poured" into

Let some repulsion term in the fluid density and a postulate so that the distribution of the fluid is always isotropic in any spatial volume

Ryan Unger

@NovaliumCompany no

I'm new here

Secret

Now let the following postulate for the properties of the fluid:

1. Given a straight line interval of length 1 m, the time fluid density is proportional to the number of divisions of the 1m interval

Slereah

You can use Newman-Penrose if you don't want tensors

it's all scalars

Newman–Penrose formalism

The Newman–Penrose (NP) formalism is a set of notation developed by Ezra T. Newman and Roger Penrose for general relativity (GR). Their notation is an effort to treat general relativity in terms of spinor notation, which introduces complex forms of the usual variables used in GR. The NP formalism is itself a special case of the tetrad formalism, where the tensors of the theory are projected onto a complete vector basis at each point in spacetime. Usually this vector basis is chosen to reflect some symmetry of the space-time, leading to simplified expressions for physical observables. In the case...

just solve this

Secret

2. Let some clock to pass through the 1m region. Then the proper time of said clock will be 1s for each divisions it passes

Now let two clocks moving through separate 1m regions, then the clock where the time fluid density is lower runs slower than the other clock

Since acceleration is given by $a=\frac{dv}{d\tau}$, under this model, it will be the velocity of a clock travelled wrt to the time fluid density. The velocity is thus given by the integral of this wrt the time fluid density

Thus it is easy to see that if the time fluid density is uniform in a region, the acceleration is zero

ok sorry, the implication of postulate 1+2 should be:

Now let two clocks moving through separate 1m regions, then the clock where the time fluid density is higher runs slower than the other clock

Now since velocity is $v = \frac{\partial v}{\partial \tau}$, under this model, it becomes the derivative of the displacement travelled by the clock wrt the time fluid density

and the acceleration is just the negative of the 2nd derivative of displacement

hmmm... , I can easily just smack the Lorentz transformation relation between displacement and time fluid density to recover the SR result, but it is not logically obvious why that is justified

hmmm....

We can perhaps consider two clocks moving across two 1m line with different time fluid density, and then consider what happens when we view the dynamics in the slow clock's perspective:

Then for a clock that travels 1m in 16s, transformed so that 16s becomes 4s, then in order to keep the velocity unchanged, the travel distance becomes 1/4 m

actually no, in the clock's rest frame, it has to perceive itself as travelling 1ms-1. Try again:

Ok, for a clock that travels 1m in 16s in the frame of another clock travelling 1m in 1s, in its rest frame it will travel 1m in 1s, whereas the other clock will travel 1m in ts

jacob1729

5:59 PM

46

Q: What if the LHC doesn't see SUSY?

A question in four parts. What are the main problems which supersymmetry purports to solve? What would constitute lack of evidence for SUSY at the proposed LHC energy scales (e.g. certain predicted superpartners are not in fact observed)? Are there alternative theoretical approaches which wou...

string-theory supersymmetry large-hadron-collider faq

Can someone comment on the latest answer to this? I feel like it's just a vague rant against string theory and in favour in LQG but don't know the area well enough to say. Eg. does LQG need SUSY?

Secret

Thus in the slow clock's frame, it is transversing more time fluid per second thus the other clock will either travelling through more dense fluid, or travelling though a shorter distance. The reverse applies when moving to the fast clock's frame, hence giving an outcome similar to time dilation in SR

Thus under this model, the constancy of the speed of light translates to:

There is a lowest possible time fluid density, given by some constant $\frac{1}{c}$, more accurately, there is a limit on how far one can expand a time fluid

and this limit is the same for all frames

The relativity of simultaneity follows nicely from how the clocks respond to the time fluid and that they registering the same number of seconds in one frame is not necessary true in some other frame

Now there is a problem: What will a light cone mean in this model

might expand this into 2D later

Anyway, this model is really motivated by something from Avengers:Endgame

> Stark: It’s the EPR paradox. Instead of pushing Lang through time, you might have wound up pushing time through Lang. It’s tricky. Dangerous. Someone could have cautioned you against it.

and furthermore, tis model is inspired from Bohemian mechanics and all the discussion between it and orthodox quantum mechanics

It seems to provide a handy way to pack away the time axes into space, thus allowing me to include a new physics phenomenon where you effectively have two time dimensions, because one of these is reduced into a fluid occupying spacetime

Also inspired by the time machine here:

You're Grounded! - English Full Walkthrough

►

@vzn What do you think, a potentially breaking way to interpret GR while allowing possibly new physics, or does not work?

dmckee

7:18 PM

Random thought. Would the site benefit from a tag for minimization-principles (or stationary-principles) to tie together then many guises of this idea?

Why or why not?

knzhou

7:34 PM

@jacob1729 LQG doesn't need SUSY, but string theory doesn't need SUSY in a way that's visible to the LHC.

jacob1729

7:45 PM

@knzhou The top answer on that post (by Lubos) seems to list several reasons for expecting SUSY to be found at the LHC. Do you think that was naively optimistic, or is the LHC data pretty damning for string theory (if not literally a killing blow)?

vzn

8:02 PM

@Secret yes its not so different than spacetime fabric idea. when the fabric is stretched it affects both space/ time. afaik the mathematics is identical to known GR except maybe in the extreme/ edge cases. the same relativistic formulas can be found in "sound travel thru a gas" (analogous to light thru space) and havent seen almost anyone remark on that in published materal. it will take a very high power genius to (1) sort it out and (2) convince others. sometimes (2) far harder than (1) o_O

knzhou

@jacob1729 I think a more clear way to put it is this:

In physics, the game is to explain as much as you can with as simple assumptions as you can.

SUSY is nice because it fixes a lot of so-called fine-tuning problems, right out of the box. But it's expensive because it's complicated and adds >100 new parameters to the SM.

However, since string theory needs SUSY, if you believe in string theory you can put SUSY in "for free". It doesn't make your worldview more complex because you already had to have it.

If you additionally want to use SUSY to solve all your tuning problems by itself, then you have to put it in at the weak scale and expect to see it at the LHC.

So this is the source of statements like "string theory implies weak-scale SUSY". It actually doesn't (which is why no weak-scale SUSY doesn't imply no string theory), instead it makes weak-scale SUSY look like a really good deal.

The long-term sociological impact, which has been in the works for a long time now, is probably yet another widening of the gap between hep-th and hep-ph. You'll get a lot of people who want to go into string theory not because they think it has anything to do with the world, but because it's high-prestige and hard.

Ryan Unger

@Slereah that book on collisions I bought uses this

I don't really get the appeal yet

Slereah

Yeah I dunno

Guess it simplifies for some cases

knzhou

People who try to bridge the gap and actually make predictions from string theory will get even more sidelined.

Like, I've seen very pure string theorists get offended when they see people try to make predictions with it.

It's like, "now you're dragging us into bad press when we didn't even care about this [the real world] in the first place", etc.

That seems to be the prevailing attitude among most grad students going in, my age.

Anyway, if you still want to go the route of string theory + SUSY + GUTs + etc., the full package, it's still totally possible. There are marginally more complicated theories (around the scale of making one or two more 1 in 10 arbitrary choices) that haven't been falsified by the LHC at all. It's just the first wave of stuff that's been cut down.

It makes sense that the first wave was totally destroyed because the whole point of those models was to look at what could be tested by the LHC.

Like, if you start looking for your lost keys by checking your pockets and don't find them, you could throw up your hands in defeat and say, "Everywhere I looked has been ruled out! The keys don't exist!" Or you could say, okay, the easiest place to check doesn't work, how about the next one?

I hope that explains some of the general optimism/pessimism you hear from different corners of particle physics.

Personally I think the LHC's the greatest bonanza ever because of all the SUSY papers I won't be reading. :P

3

Emilio Pisanty

8:33 PM

@dmckee you mean, a tag that would cover both Hamilton's principle and Fermat's principle? I reckon there's about a 0±0.1% chance that it will end up being used correctly if it's scoped that broadly.

@PhysicsMeta any takers on what caused the recent spike on terrible questions on meta that should've been posted on main?

just a random fluctuation?

dmckee

@EmilioPisanty Uhm. Fair enough. One need only follow [mathematical-physics] to see the evidence.

Ryan Unger

@knzhou this is why math is better than physics; branches are not invalidated because of stupid things like reality

Emilio Pisanty

If you want a conceptual introduction, just read the first ~3 chapters of Feynman vol III. Or, for slightly more concepts, try the first chapter of Sakurai. Anything more will require math. — knzhou Jan 17 '16 at 22:42

look at @knzhou answering questions in comments ¬¬ =P

skullpetrol

@RyanUnger welcome stranger :-)

Emilio Pisanty

ditto

This book is quite well suited for mathematicians. It may also be interesting for mathematicians to read how a mathematical concept like distributions first arose in physics in a non-rigorous heuristic way. — Count Iblis Jan 17 '16 at 23:24

Quantum Mechanics by Alastair Rae is a good introduction, the recommended text at Cambridge for mathematics undergraduates. amazon.co.uk/Quantum-Mechanics-Sixth-Alastair-Rae/dp/1482299‌186/… — user85798 Feb 16 '16 at 23:06

cows

8:50 PM

Finished some string calculation in a world space. Walking to the beach while listening to hip hop

I meant wierd space.

Texting this via mobile

Physics Meta

9:08 PM

-1

Q: Why is this question asking about lectures closed as a duplicate?

This question is currently closed for being a duplicate of this question. The closed question asks about recommendations about video lectures for quantum lectures while the second question asks about books. The answers to the second question do not contain information about video lectures. Why i...

discussion scope closed-questions resource-recommentation

Emilio Pisanty

@PhysicsMeta because it is a duplicate.

cows

9:29 PM

Some people just waived at me and said h in a friendly way i, I don't know them but this has made my day.Yay!

May be the outside world is not so bad lolz

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