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fqq
fqq
00:34
@Obliv if there's a weight hanging there's tension
in principle there's no need for the string to be fixed at both ends, you could have one end free to move (trasversally) on a rail or something, you still have tension and derive the wave equation in the same way, with different boundary conditions
with a weight it's probably complicated if you want to do it properly, the modes will be couple to the dynamics of the weight
 
1 hour later…
Obliv
Obliv
01:50
@Fqq if the driving force is only vertical, how could the wave move horizontally?
 
3 hours later…
Ghoster
Ghoster
05:12
Ghoster here, waiting for FlatterMann
FlatterMann
FlatterMann
Hi Ghoster.
Sorry, I didn't want to appear testy about it.
Ghoster
Ghoster
So let me start by saying that I am not invested in the WdW equation being either correct ir even sensible.
However saying that it is “not even wrong” is very strong language … one step above crankery.
John Rennie
John Rennie
Wheeler de Witt equation?
Ghoster
Ghoster
Yes. I don’t see Hawking and Vilenkin (my postdoc advisor) as pursuing “not even wrong” research.
FlatterMann
FlatterMann
I honestly think that it is not even wrong. I am sure that one can construct a quantum theory of spacetimes. Whether it is as simple as WdW suggests, that I don't know, but one has to start somewhere. The question for me is whether this will ever connect to the real world. I don't believe it will.
Ghoster
Ghoster
05:16
They were interested in it because it has the potential to explain the “initial conditions” of the universe.
FlatterMann
FlatterMann
No offense, but thousands, if not tens of thousands of string theorist have done just that whole moving the goal post at least half a dozen times. That's just part of being a theorist these days... the experimental and observational data bone is empty.
Ghoster
Ghoster
Why do you think it can only describe empty universes? I don’t think that’s correct.
FlatterMann
FlatterMann
The problem with "initial conditions" for the universe is the assumption that the universe even had a beginning in the sense of a differential equation.
How does matter and radiation jump out of an empty equation?
This is all very much 1950s and 1960s style thinking.
Ghoster
Ghoster
The wavefunctional in WdW is a functional f all the fundamental fields.
Not just the metric
FlatterMann
FlatterMann
I think we are getting much closer to the truth with conformal cyclical models... and then the "initial condition" question becomes irrelevant.
How do you know what the fundamental fields are?
The standard model is a fit below 1TeV. There is nothing fundamental about it.
Ghoster
Ghoster
05:21
OK, that’s fine. Are you studying physics now? Doing physics now?
We have no idea what the fundamental fields are.
My point is that the WdW equation is not just sbout gravity.
FlatterMann
FlatterMann
I am long retired. I used to work one of the CERN detectors a long time ago. Don't get me wrong, they are not trying to answer the fundamental questions there. They are still trying to figure out what happens around or slightly above 1TeV, which is nothing compared to what WdW is trying to address.
Ghoster
Ghoster
Yes, I understand. OK, appreciate your point of view.
FlatterMann
FlatterMann
A framework that looks like the Schroedinger equation and that is empty because we don't have anything to stuff into it is stiil useless.
Ghoster
Ghoster
I am also retired.
FlatterMann
FlatterMann
Maybe I a too old, already, but the simple experimental/observational fact is that we are absolutely clueless about what is beyond the accelerator scale.
I have seen literally thousands of presentations by theoreticians about what could be there. We could pin them to the wall and throw darts and that might be a better strategy than even more theory at this point.
Ghoster
Ghoster
05:25
Yep. Before we go… given that situation, what do you think theorists SHOULD be doing?
Just practical things like condensed matter?
FlatterMann
FlatterMann
I don't think there is much theorists can be doing at the moment. Einstein didn't work in a vacuum. He had observational data. Feynman and Schwinger knew what they were after and that goes on... but the gap to "the universe" is, at the moment, simply too large. Nobody is going to jump over that.
Ghoster
Ghoster
OK, nice to chat with you!
John Rennie
John Rennie
@Ghoster theorists should be allowed to do what they want. The cost of supporting a few theorists isn't exactly a huge burden on the world economy, and we already support mathematicians and philosophers whose work is never likely to have any impact on everyday life.
FlatterMann
FlatterMann
Boy did condensed matter chance since I was in school! I have to say that there are a lot of interesting systems there. Not my cup of tea, but still.
Ghoster
Ghoster
Yes, that’s my opinion. But I was a theorist!
@JohnRennie
FlatterMann
FlatterMann
05:29
I am the last person on Earth who is suggesting to reduce science budgets. Theorists just have to work through all of the "It's not even wrongs" and they are doing it diligently. One has to admire the tenacity.
John Rennie
John Rennie
@FlatterMann It sounds to me like you read Woit's blog once too often :-)
Ghoster
Ghoster
Thete is a big difference between “WRONG” and “not even wrong”.
FlatterMann
FlatterMann
Please, don't mention that name. :-)
John Rennie
John Rennie
@Ghoster What area did you work in?
FlatterMann
FlatterMann
Let's just say that even as an experimentalist I have evolved from thinking that the universe is a spherical cow that is homogeneously covered in milk.
Ghoster
Ghoster
05:33
@FlatterMann I think the only reason you think the WdW eqn is “simple” is that you haven’t looked at what $
FlatterMann
FlatterMann
I am now more of the opinion that the universe is more like swiss cheese, I am just not sure whether we are living in the cheese part or the hole part.
Ghoster
Ghoster
H is.
FlatterMann
FlatterMann
So if DwD can model swiss cheese, then maybe I am even in philosophical agreement with it.
Ghoster
Ghoster
If by Swiss cheese you mean a spacetime with a lot of holes, I think it can.
FlatterMann
FlatterMann
OK, since we are talking opinions: what are theorists thinking these days about the homogeneity and isotropy assumptions? Are we going to detect that the observable universe is, after all, not one or the other or both?
Yes that is what I mean. Are we looking at a much more complex topology for the "entire universe", unobservable as it is?
Ghoster
Ghoster
05:39
That would be very exciting but I wouldn’t hold my breath
FlatterMann
FlatterMann
I don't know if I have enough breath left to wait for the whole universe surveys... that's the trouble.
Ghoster
Ghoster
Yep. It’s getting to be late, so I’ll say g’bye.
FlatterMann
FlatterMann
Is there a bit of a "saddle" in our stretch?
Nice talking to you.
Ghoster
Ghoster
Same
 
6 hours later…
Slereah
Slereah
11:11
user image
Did you know that cats are invariants
Feynman_00
Feynman_00
11:39
@Slereah Lol I used the same example with apples, pears and bananas to understand the physicist's definition of tensor
"A random set of three numbers $(a,b,c)$ does not transform as a vector" seemed quite weird as I read it as $(a,b,c)=ae_1+be_2+ce_3$ . Only later I understood what they really meant and came up with the fruit example. I still consider that the worst way to put it D:

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