The h Bar

4:52 AM

@DavidZ Yep.

8:27 AM

@tttt I have read from some research group claiming a black hole is a condensation quantum state comprising a great amount of gravitons, which are bonsons..

John Rennie

@ayc hi

ayc

@JohnRennie Hello!..You have said that : the collapse of the wavefunction on observation is a random process, so the universe cannot be deterministic.MY QUESTION:Is it possible that we haven’t yet discovered such a law..A Law that can predict what out of N possibilities will happen .Is there any mathematical proof to say that this property :the collapse of the wavefunction on observation is random process is the fundamental ..i.e it is the property that you can never disprove?

John Rennie

All of QM is based upon the assumption that the collapse is random, and so far that assumption seems to be holding up.

ayc

So,is it just only an assumption?

John Rennie

Of course it's possible some deeper theory exists that we haven't discovered yet, but then you can always say there's something we haven't discovered yet.

It's also just an assumption that the speed of light is constant.

All of physics is based on assumptions. We do experiments to test those assumptions.

So far no experiment has suggested that the collapse isn't random.

ayc

8:35 AM

So according to current level of understanding universe seems to be non-determinitsic...right?

John Rennie

Yes

We should probably be more precise about this. It's only the collapse process that is non-deterministic.

And at the large scale where we can take a statistical average physics is effectively deterministic.

ayc

@JohnRennie Are there any ongoing experiments which assume that wave function collapse isnt random?

John Rennie

There are interpretations of quantum mechanics that try and get around the non-deterministic nature of the collapse process, for example the Many Worlds interpretation. But even in this interpretation for any particular observer the collapse is still random.

@ayc I'm not aware of any. I suspect you'd struggle to get funding to test something that everybody believes to be true.

ayc

@JohnRennie But,someone must've questioned it and also worked maybe!

John Rennie

@ayc in the early days of QM the subject was discussed a lot. I'm not that interested in the history of QM so I don't know that much about the early discussions.

ayc

8:44 AM

@JohnRennie From what I understand it seems like you can never prove experimentally Many worlds interpretation....can we?

John Rennie

@ayc correct

But then all the interpretations suffer from the same problem that it's hard to see how they could ever be tested experimentally.

That's why many physicists are impatient with the subject of quantum interpretations.

ayc

8:58 AM

@JohnRennie I have just read the EPR paradox......What do you think of it...I mean it questions heisenbergs principle right?.....all the theories which tried to resolve EPR paradox seem to claim that wave function collapse is deterministic..And there doesn't seem to be any experiments to support the theories....If heisenbergs uncertainity principle is true then we must be able to explain the EPR paradox right?

John Rennie

It isn't a paradox

There is no causation. Observing the spin of one particle to be up does not cause the spin of the other particle to be down.

ayc

@JohnRennie I don't get you .could explain it in a simpler way?

John Rennie

@ayc to be honest I struggle to raise much interest in discussing the subject.

@ayc the thing is that while this undoubtably seems new and interesting to you it seems old and boring to any experienced physicsts.

There must be a million web pages out there in Googlespace discussing the EPR paradox (which isn't a paradox).

Anyhow I need to work now for half an hour or so.

ayc

@JohnRennie Al right!.......c u later......Thank you for your time!

Slereah

12:58 PM

People mostly misunderstand the point of EPR

The first two measurements are not surprising at all

The weird part is when you do the non commutative measurements

M.N.Raia

4:37 PM

Good morning/afternoon/night for everyone!
I would like to ask a quite general question about differential geometry concerning the technic of remove singularities of a given metric (i.e. from a spacetime).
After you read the introductory books on GR, the one have encountered coordinate changes like eddington-finkelstein coordinates to remove the singularity in r=2M.
So, I've read an article that the authors leave open the possibility to remove some possible singularity. But how can I do that? I mean, which steps that I have to recognize to,at least, be able to try something?

ACuriousMind

@M.N.Raia There's no standard method to remove such coordinate singularities. However, you should look at things like the curvature scalar at the singularity - if curvature, too, becomes singular, then the singularity is not removable and not an artifact of coordinate choice, but physical.

For a removable singularity, you essentially need to guess better coordinates, I'm afraid.

M.N.Raia

5:00 PM

Thanks @ACuriousMind =)

kartik c.p

6:34 PM

did any body bother about 369

ACuriousMind

6:44 PM

@kartikc.p Who or what is '369'?

kartik c.p

@ACuriousMind. youtu.be/GnEWOYKgI4o see this video clip

ACuriousMind

Ah. I don't think anyone here bothers with such pseudoscience.

kartik c.p

sorry if you are not intrested

@ACuriousMind . What kind of info is bieng transverd by entangled partiles . and how can we even guess that they are entangled

ACuriousMind

7:00 PM

Sorry, I do not understand what you're saying.

kartik c.p

the information that bieng transverd by entangled particles

ACuriousMind

"bieng transverd"???

kartik c.p

i mean shared

ACuriousMind

Oh, do you mean being and transferred? There is no information transferred via entanglement, that's the no-communication theorem.

kartik c.p

ya

i am not physicist so go easy on me

@ACuriousMind what makes us to consider that they are entangled to each other

ACuriousMind

7:10 PM

The definition of an entangled state is one in which you cannot assign a single specific state to the individual particles. You can't actually measure directly whether a state is entangled or not.

For more on entanglement and how it's not communication, see the answers to physics.stackexchange.com/q/3158/50583 and physics.stackexchange.com/q/109861/50583

danielunderwood

@ACuriousMind interesting...another thing for my "obvious, but never realized" list

kartik c.p

@ACuriousMind thankyou for your patience

danielunderwood

(the measurement part)

ACuriousMind

@danielunderwood That's incidentally why Bell experiments have to close all manner of loopholes in order to show that there is something fundamentally non-classical about QM (and even then they don't show entanglement, they only show "either non-local or non-realist"!). If we could directly show that a state is entangled in the sense that you cannot assign states to its subsystems, we would have killed off the realists a long time ago

Essentially, this is one of the two reasons we have to quibble about interpretations at all, the other being the measurement problem itself

Slereah

8:00 PM

@ACuriousMind i dunno about that

You can always remove such a singularity by considering a local coordinate patch

Also you can check if it's a coordinate singularity by parallel propagating a frame there

ACuriousMind

Better ping @M.N.Raia, not me ;P

bolbteppa

8:28 PM

3, 6 and 9

I've never understood this Tesla fascination

danielunderwood

I prefer 2, 4, and 8

bolbteppa

I'm partial to 143

urbandictionary.com/define.php?term=143

What now Tesla

danielunderwood

You can't deny that nature is powers of 2

ACuriousMind

@danielunderwood Bah, humbug! The only powers we need are powers of 10 (aka "orders of magnitude")

bolbteppa

42 may be a power of 2 in like binary right :p

independent.co.uk/life-style/history/…

danielunderwood

8:39 PM

@ACuriousMind your orders of magnitude are off. I measure things as $a \times 2^n$!

ACuriousMind

...so I have two orders of magnitude more limbs than heads? :P

danielunderwood

Now you're getting it!

Captain Bohemian

10:53 PM

is W-algebra related to W*-algebra?

David Z

...they annihilate with each other and you get 2D gamma algebra :-P

(I don't actually know)

Captain Bohemian

11:17 PM

I get the definition of W*-algebra in mathworld.wolfram.com/W-Star-Algebra.html, and that of W-algebra in ncatlab.org/nlab/show/…. I actually also see the Wikipedia article for W-algebra, but none of these brief introductions mentions to whether W-algebra and W*-algebra are related.

user301074

hmmm, an random question... Is possible time travel to past without creating paradoxes?

David Z

@Zober Well as far as we know it's not possible to time travel to the past at all, so according to current science the answer is no. If backward time travel is possible, then the answer to your question depends on how the time travel works. (It also depends on your definition of "paradox".)

user301074

In "paradox" i mean a causal contradiction.

user301074

I was thinking about it when reading a text about the "Causal structure" of spacetime

user301074

11:33 PM

Like the sentence's "X causally implies Y", and if "X causally implies Y" then "Y causally implies X"

user301074

where X chronologically "precedes" Y

David Z

If I understand what you mean, though, that's not a contradiction. It's perfectly consistent.

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