Lecture 3 | Modern Physics: Special Relativity (Stanford)

[@zeweichu550]

I like it when the professor eats cookies in the lecture like he is just at home teaching his grandkids some knowledge.

[@EdSmiley]

It is a relief to see that Dr. Suskind can't remember which are called the covariant and which the contravariant indices, I always get those mixed up too.

[@joabrosenberg2961]

importance of invariants 26:00; four-vectors 28:00; What a field is 46:00; Co-variant and Contravariant vectors 57:30; Wave on a string 1:10:00; 4-dimensional field 1:24:00

[@deloford]

brilliant teacher, i wish i had had a physics teacher half as good as lenonard

[@mohameda.444]

There is a tiny mistake here @ 15:52, this is a passive rotation of axes not an active rotation of a vector; hence the negative sign in front of sine(theta) should be downstairs not upstairs; try it yourself for the point (4,3) in the original coordinates; after rotating the axes; the point will be further left to the new y’ axis (which means a large x’ coordinate value) yet below the new x’ axis (which means a negative y’ coordinate value).

[@noobmartin]

I believe that increased knowledge in the instructor increases the quality of the lectures. Most teachers are not professors, unfortunately. :)

[@piyushchakravarti333]

Stanford University lecturer on QM helped me lotthe special the of relativity is also good to improvise our old concepts

[@pablo_CFO]

1:01:40 i don´t get it, it is supose that we have a summatory only when the index of two terms are in different positions. The partial derivative of phi respect to dx super Miu multiplied by dx super Miu it is not a summatory over Miu, because the index is in the same position in both terms, so i have to do every index individualy (when miu=0,1,2,3) and i will have a vector that have the change of phi en every component, but if i change the partial derivative for phi sub miu (that in theory are the same), and i do the multiplication with dx super miu i will have a summatory over miu, because in that case i have a term with a lower index and the other term with an upper index, so... how dphi/dx super miu is the same that phi sub miu?, if i multiply each one for dx super Miu i have different results.

[@TheAlbi28]

Pablo Ramirez Infact Einstein's convention is about any double (or more) indeces. It doesn't matter if they are up or down, the important is they have to be attached.

[@pablo_CFO]

so...basically the index works as the same way as the normal tensor notation, i thought that in relativity that "rules" will change a little bit.

[@Ambient_Scenes]

@loopantenna I agree, but unfortunately from my experience theres one of those people in every phys class (and probably most other classes).

[@wildfire5932]

his blog isn't even updated anymore. that sucks

[@lsbrother]

answer - 'a barometer'

[@fjolsvit]

0:19:42 For shame. Argument by symmetry. The paintbrush gedankenexperiment.

[@ffddssaavvccxxzz]

very hard hhhhh... but this teacher is very good.....

[@bartkwezelstaart9306]

Since (for the moment) i'm specificaly interested in special relativity and i don't have a lot of time, is it nessasary that i watch all of the classes about fieldtheory aswell? I you think you can judge, please tell me what i can and cannot skip to be able to understand all of special relativity without having to worry about fieldtheory(if that is possible) Thank you !

[@shiddy.]

it's been 4 years, how did it go?

[@nazishahmad1337]

Altough I guess answering now won't be helpful to you but there are lectures by prof. Susskind only on special relativity and this set of lec is particularly for field theory .

[@bartkwezelstaart9306]

@@nazishahmad1337 thank you for answering anyway :)

[@clubsandwedge]

the problem is 99% of polemics are just trying to get them to come to their own opinion. polemics is all about rationality primarily and evidence secondarily.

[@williamwalker39]

The speed of light is not a constant as once thought, and this has now been proved by Electrodynamic theory and by Experiments done by many independent researchers. The results clearly show that light propagates instantaneously when it is created by a source, and reduces to approximately the speed of light in the farfield, about one wavelength from the source, and never becomes equal to exactly c. This corresponds the phase speed, group speed, and information speed. Any theory assuming the speed of light is a constant, such as Special Relativity and General Relativity are wrong, and it has implications to Quantum theories as well. So this fact about the speed of light affects all of Modern Physics. Often it is stated that Relativity has been verified by so many experiments, how can it be wrong. Well no experiment can prove a theory, and can only provide evidence that a theory is correct. But one experiment can absolutely disprove a theory, and the new speed of light experiments proving the speed of light is not a constant is such a proof. So what does it mean? Well a derivation of Relativity using instantaneous nearfield light yields Galilean Relativity. This can easily seen by inserting c=infinity into the Lorentz Transform, yielding the GalileanTransform, where time is the same in all inertial frames. So a moving object observed with instantaneous nearfield light will yield no Relativistic effects, whereas by changing the frequency of the light such that farfield light is used will observe Relativistic effects. But since time and space are real and independent of the frequency of light used to measure its effects, then one must conclude the effects of Relativity are just an optical illusion. Since General Relativity is based on Special Relativity, then it has the same problem. A better theory of Gravity is Gravitoelectromagnetism which assumes gravity can be mathematically described by 4 Maxwell equations, similar to to those of electromagnetic theory. It is well known that General Relativity reduces to Gravitoelectromagnetism for weak fields, which is all that we observe. Using this theory, analysis of an oscillating mass yields a wave equation set equal to a source term. Analysis of this equation shows that the phase speed, group speed, and information speed are instantaneous in the nearfield and reduce to the speed of light in the farfield. This theory then accounts for all the observed gravitational effects including instantaneous nearfield and the speed of light farfield. The main difference is that this theory is a field theory, and not a geometrical theory like General Relativity. Because it is a field theory, Gravity can be then be quantized as the Graviton. Lastly it should be mentioned that this research shows that the Pilot Wave interpretation of Quantum Mechanics can no longer be criticized for requiring instantaneous interaction of the pilot wave, thereby violating Relativity. It should also be noted that nearfield electromagnetic fields can be explained by quantum mechanics using the Pilot Wave interpretation of quantum mechanics and the Heisenberg uncertainty principle (HUP), where Δx and Δp are interpreted as averages, and not the uncertainty in the values as in other interpretations of quantum mechanics. So in HUP: Δx Δp = h, where Δp=mΔv, and m is an effective mass due to momentum, thus HUP becomes: Δx Δv = h/m. In the nearfield where the field is created, Δx=0, therefore Δv=infinity. In the farfield, HUP: Δx Δp = h, where p = h/λ. HUP then becomes: Δx h/λ = h, or Δx=λ. Also in the farfield HUP becomes: λmΔv=h, thus Δv=h/(mλ). Since p=h/λ, then Δv=p/m. Also since p=mc, then Δv=c. So in summary, in the nearfield Δv=infinity, and in the farfield Δv=c, where Δv is the average velocity of the photon according to Pilot Wave theory. Consequently the Pilot wave interpretation should become the preferred interpretation of Quantum Mechanics. It should also be noted that this argument can be applied to all fields, including the graviton. Hence all fields should exhibit instantaneous nearfield and speed c farfield behavior, and this can explain the non-local effects observed in quantum entangled particles. *KZbin presentation of above arguments: kzbin.info/www/bejne/qZazlX1tq7iErLM *More extensive paper for the above arguments: William D. Walker and Dag Stranneby, A New Interpretation of Relativity, 2023: vixra.org/abs/2309.0145 *Electromagnetic pulse experiment paper: www.techrxiv.org/doi/full/10.36227/techrxiv.170862178.82175798/v1 Dr. William Walker - PhD in physics from ETH Zurich, 1997

[@lsbrother]

1:17:36 he's wrong about not needing a double integral sign - I can see where he's coming from but strictly speaking you do need them both. With just one sign and dtdx you have a form with a perfectly legitimate but different meaning.

[@timewalker6654]

How the hell suskind looks younger in 2012 videos

[@lsbrother]

but a barometer is just a normal household object - surely any reasonably educated person knows what one is and that it measures air pressure - you don't need to be either a engineer or physicist

[@timewalker6654]

But how the hell it do that, to know this you need to be

[@SKCSK792]

0:30:00-0:50:00

[@SuperMagnetizer]

Hi clubsandwedge, Precisely. What would Galileo say about that? True scientists question everything. Only the "religiously devout" obsequiously & slavishly question nothing.

[@Kerysyk]

1:08:40 is d(WiFi)^2 ... :D

[@clubsandwedge]

'no polemics', why not?

[@ggankinboon]

I don think that violin string is a good example.... just confuse... but it can explain the lagrangian... and how it transform... ok... I don know

[@lsbrother]

41:50 'What's a pressure meter called?'

[@fjolsvit]

susskindsblogphysicsforeveryo­ne.blogspot.com is unfortunately not active.

[@curselikfucknsailors]

you dare question the authority of leonard susskind? may the gods be gentle with your soul

[@sabrewolf479]

Dr. Susskind is a scientist. Science and scientists love to be questioned. Gods are authoritarians who hate questions and punish those who question. Hence the schism between the lovers and discoverers of truth and the followers of religion.

[@lsbrother]

'oh - what's a barometer' - he's a prof of physics and he really doesn't know what a barometer is?!

[@pphilosophy2156]

Physics has what's called a division of labor between the experimental and the theoretical parts. Being a theoretical physicist whose deep into the subject(s), he has probably just crammed his brain so full of abstract math and theoretical concepts that the practical stuff can sometimes get jumbled up. I'm sure he's at one point learned what a barometer is, but I'm equally sure that as the lecture wore on and his focus was on the minute details of the lecture at-hand, he just had a lapse of focus. I haven't watched yet, but I'm about to. Thanks!