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123
4:02 AM
Hi...
 
 
1 hour later…
5:08 AM
So I recently heard about Lisi's E8 Theory, but it looks to me as though it violates the Coleman-Mandula no-go theorem. I don't know nearly enough about GUTs to know if this is somehow circumvented, but if this is the case, why are so many people rallying behind it?
 
5:28 AM
Are people rallying behind Lisi's theory? I thought it had been largely dismissed. I recall that Jacques Distler pointed out a major flaw in it though I forget the details.
 
@NiharKarve this is a strong takedown of his 'theory'
 
Hmm, maybe it was mostly just the media capitalising on the chance to promote a new 'elegant theory of everything'
Speaking of which, which are the (on the whole) reliable pop-sci media outlets?
 
@bolbteppa Motl is a notoriously impartial and balanced observer
 
@JohnRennie albeit only within the sphere of physics
Yeah, I like Quanta
 
Nobody takes this stuff seriously, people knew for decades that $E_8$ wouldn't be good enough because it only admits real irreps, $E_6$ is the best one can do to get complex irreps (needed for things like chiral fermions) and people have talked about $E_6$ as a GUT
 
5:43 AM
Hmm, my temperature is up this morning.
Though only by half a degree so I don't think my death is nigh just yet.
 
Fahrenheit or Celsius?
 
What is this Fahrenheit of which you speak?
 
I think I'm in the minority then
 
The Lisi stuff is great to motivate learning group theory and seeing how careful one has to be with it
The end of the wiki is written like this is a serious theory, e.g. "also thought to work in E8"...
 
vzn
6:02 AM
@bolbteppa photoshopped crowd of women in bikinis is a "strong takedown" of his theory? lol!
@NiharKarve am not going to contradict room owner JRs take on it as "largely dismissed" but you might find the vignette/ profile/ interview in hossenfelders Lost In Math interesting/ amusing, or maybe merely entertaining :) amazon.com/Lost-Math-Beauty-Physics-Astray/dp/0465094252
 
I had to restrain myself from including that one/sole proviso (from a person with their own charitable perspective on how bad theoretical physics is nowadays) about people taking it seriously haha
 
vzn
taking what seriously? Lisi or LuMo? :P
still not really following who all youre referring to :|
 
Lost in Math adding him to the book as a representative of something...
 
vzn
are you saying hossenfelder has a "charitable pov on how bad theoretical physics is nowadays"? actually it seems quite uncharitable at times but it seems also that was her intention o_O but personally find the brouhaha of hossenfelder talking facetiously about lisi to be kinda funky... one clown joking about another one? hard to say exactly...
 
Humor doesn't necessarily always come off in text :p
 
vzn
6:11 AM
so BT what is your top GUT/ ToE candidate if not lisi then? :P
 
A huge problem with quantizing GR is renormalizability issues, this has happened in the past:
"The non-renormalizability of the V-A theory of weak interactions has led to a long search for renormalizable theories. The problem was not solved by finding a new method to deal with the divergences of the V-A theories. Rather, it was solved by considering the V-A theory as a special limit ($M_w = \infty$) of a unified gauge theory of weak and electromagnetic interactions. The success of this approach was due to the theoretical proof that the gauge theories are renormalizable"
Those experimental proofs took years also, these critics are criticizing physicists who extend modern day theories for doing the exact same thing that was done in the past, like for literally following the same path which has worked before, it really is astounding and should be called out for being pure anti-science especially since the target audience is laymen
 
It's important to bear in mind that it's the rabid ends of the spectrum that make the most noise and get the most attention. Most physicists are interested in anything that seems to have a chance of working and don't feel the need to shout about it.
 
vzn
huh, this new book by smolin comes up on related list wrt hossenfelder, dont think noticed it previously. looks very cool, gotta get/ read this asap! Einstein's Unfinished Revolution: The Search for What Lies Beyond the Quantum amazon.com/Einsteins-Unfinished-Revolution-Search-Quantum/dp/… just from the title alone, am sure all the copenhagenists will strongly disapprove!
 
Yeah
 
vzn
"most physicists" are probably wrong, lol
 
6:20 AM
99% of all ideas are wrong. The problem is distinguishing the 1% from the rest.
 
vzn
it seems a lot of physicists are not really interested in new ideas...
 
I don't believe that's true, though I appreciate that you may be experiencing some selection bias.
 
vzn
possibly! or maybe am not experiencing any bias and it is projected on me (by others with bias, lol). but thx for your "appreciation" anyway :)
might as well quote the grandfather of the obscurantism himself...
Physics is not about how the world is, it is about what we can say about the world --Bohr
3
 
 
2 hours later…
8:49 AM
@Philip ... if you happen to frequent the chatroom
 
@MoreAnonymous Check out the last line, "The right hand side is essentially the first derivative..."
 
@Philip Yea you are correct :)
 
 
1 hour later…
10:16 AM
How does ozone absorb a range of UV radiation, instead of a single wavelength? Is it some kind of Doppler shift due to the velocity of the molecules?
 
In a gas molecule electronic transitions are always associated with a change in the vibrational and rotational quantum numbers.
So we never see a sharp line, we see a mass of sharp lines corresponding to different changes in the rotational and vibrational quantum numbers.
But these lines are closely spaced, and at all but the lowest pressures these lines are broadened by collisional broadening so the merge into a single broad absorption.
If you Google for uv absorption spectra of ozone you'll find you can just about see the wiggles in the spectrum corresponding to the different vibrational transitions.
 
10:51 AM
Thanks a lot @JohnRennie
 
Single atoms give single sharp lines because an atom can't rotate or vibrate so you don't see any associated rotational/vibrational transitions.
 
123
11:31 AM
Hi @JohnRennie @ACuriousMind
What is the benefit of Electric Potential over Electric Field??
What are the cases of where electric field is beneficial not electric potential and vice versa???
 
 
1 hour later…
12:56 PM
Does the disjoint union of invariant hyperbola in $\Bbb R^{1,1}$ form $\Bbb R^{1,1}$ itself?
 
@123 It's much easier to talk about circuits or plates in terms of voltage than in terms of field strengths, is it not?
 
@ACuriousMind: The PM that I sent you was just before you dealt with the problematic user. Thanks for that. And yes, since you've done that, thanks for stepping in, and there is no necessity to respond to my PM.
(I'm tired of it anyway lol.)
 
@123 There are also technical reasons we want a potential - you can write down a Lagrangian formulation of electromagnetism with the 4-potential as the dynamical variable but you cannot find a (nice) Lagrangian formulation where the electromagnetic field is the dynamical variable; but even without that it's often more convenient to think in terms of the potential - a single number - instead of the electric field that's a vector.
The potential makes manifest that there are not three independent quantities here.
 
1:19 PM
Loved the video
It is always look stupid, when people use the wrong representation of space time fabric
 
0
Q: May I ask questions about physics lab equipments?

MarkI'm looking for a specific lab equipment but I don't know the exact English words to describe it so my searches are useless. To give an idea I'm interested into a gyroscope with gimbals and a motor to sustain the spinning over the time. Does this type of question is accepted in the Physics are of...

 
1:50 PM
how are tauons and tauon-neutrinos produced? I see muons and muon-neutrinos can be produced by the decay of pions. So what kind of particle can decay to produce tauons and tauon-neutrinos?
 
@CaptainBohemian Weak interaction or EM
ie $$e^+ + e^- \to \tau^+ + \tau^-$$
Is a valid process
If you want more meson-focused processes you can look them up in the PDG book
Also I guess technically gravity could produce tau particles?
It probably makes a fractional amount of Hawking radiation
 
When we use the word "connection" on a vector bundle in physics are we referring to the matrix of 1-forms that acts on entire frame fields or a single 1-form that acts on individual vector fields?
 
2:56 PM
Usually "connection" in physics refers specifically to the 1-form added to the covariant derivative
or its components, yes
rather than ie the derivative itself or a section of the horizontal bundle or whatever else
 
3:37 PM
@JackRod My only nitpick: Where is time dilation in that animation
otherwise it seemed to fit that waterfall analogy of blackholes
 
Is there any iitian here?
 
4:32 PM
Just to be sure I've got this right, if I have a vector valued p-form and I partially contract it with $p$ vectors, does the resulting scalar (from the partial contraction) just multiply the components of the resulting vector?
 
123
4:45 PM
Hi guys...
What is the relationship called.
Change in KE = Change in PE
Is there any special for this?
 
Conservation of energy
 
123
Thanks
 
Why does (2) extend the definition of (1) to all real numbers except the non positive integers? By the way, for $\alpha=0$, $\Gamma(-1)$ in (2). Is this defined?
 
The gamma function isn't defined for non-positive integers
 
5:15 PM
@Charlie Right, and neither for $0$ I suppose.
 
non-positive integers includes 0 yes
 
Correct.
 
 
2 hours later…
7:03 PM
in the discussion about neutrino oscillation, is the mass eigenstates the superpositions of flavor eigenstates?
 
 
4 hours later…
10:46 PM
@bolbteppa I've seen. Are there any rumors on whether Muon g-2 will confirm the discrepancy??
 
11:19 PM
It is easy to see that the Earth’s gravitational acceleration g and the vertical direction k depend upon position. The Earth is approximately a symmetric sphere which exerts its gravitational force as if all its mass were at its centre. Thus, if the value of g at a point on the Earth’s surface is g1, then the value of g at a height of 6,400 km (the Earth’s radius) must be g1/4 approximately.
why go is divided by 4???
 
@Stupidquestioninc because the Newtonian gravitational force has the distance squared in its denominator
 
@ACuriousMind g=mG/r^2 are you taking about this?
 
ah still don't get it. How does distance squared is related to g1 being divided by 4
 
$g_1$ is the value at $r = R_e$ ($R_e$ being the Earth's radius). So at $r = 2R_e$, you get $g_1/4$.
just plug it in
 
11:29 PM
so 6400km is twice as far as earth's surface distance?
I was thinking the same
 
yes, what you quoted explicitly tells you that: "[...]value of g at a height of 6,400 km (the Earth’s radius)"
naturally, something at a height of the Earth's radius above the surface is at twice the Earth's radius distance from the center
 
well that is weirdest fact I ever saw
 
I'm not sure what you mean
 
Earth's radius above the surface is at twice the Earth's radius distance from the center
Ok i am off
 
it's...just the definition of what "the Earth's radius" means
 
11:32 PM
thanks sir
hope you have fun today
 
you're welcome (but please don't call me 'sir' :P)
 

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