Special Relativity | Lecture 1

There are 2 ships passing each other.

Ship1 at rest at top.

10;00 10;00
T--------------------N
<--- N----------T
10;00 10;02

Ship2 at rest at bottom.

10;00 09;58
T----------N --->
N--------------------T
10;00 10;00

Are the 2 ships passing each other once or twice?
T1 passes N2 twice. T1 passes N2 when the clock at N1 reads 9;58. T1 passes N2 again when the clock at N1 reads 10;00. If T1 meets N2 once then what is the time displayed at N1 when this happens?

Great video! Really enjoyed it.

Stop calling nonc onstants constants. Love you so much. Angel

The professor looks like Mike Erhmantraut

All of this is a short walk to linear algebra. @1:40:20 there is some digression on length in another frame. Just pump it through [ [1 -k] [-k 1] ] * (Lorenz "constant" based on V) you can give intuition on skew, almost like a rotation of X and T, like watching rows of wheat while on a train. V scales T and V heavily. Thank you for this on-line lecture, it is what television promised, but failed to deliver on universal education. The internet has revolutionized education: it boils down to the will of the learner. The world is your oyster, truly, finally, really.

He looks like the elderly in the game Burglin Gnomes

Question: Suppose the 3 friends on the train just synchronized their watches, at 12:00 Fred and Seymour flash their lights, and Mary, expecting them to be simultaneous, instead notices Seymour's light is late. Doesn't this tell her not only that her reference frame is moving, and by how much? And thus violate all reference frames are the same?

Why is Prof Susskind shadow 4 on the right wall and 3 on the left?

Am the only one who came here intentionally

One mistake at 19:54, the second x' should use t', not just t, i.e. x' = - (c + v) t' note the prime on t. Hence t is not t' etc.

You comments here are really stupid. Watching someone who dosent know and he pretends to know.

Can somebody please explain as to how does it make sense that there are moving inertial reference frames (relative to a inertial frame) but their clocks are synchronised at different times when viewed from other inertial frame? 33:12

There are what I believe to be "AI slop" of Leonard Susskind lecturing on physics, but the the lectures don't strike me as authentic. Here's one:
https://youtu.be/AZ9drcvM4sM?si=Y1dhn_wbBqvl5QyD

How can this impersonation be stopped if it is impersonation? There are also similar videos (a whole pile of them) impersonating Richard Feynman lectures.

I am taking online courses online from Texas A and M

Very respectfully My teacher

Here is the real solution for special relativity. Sorry I found this, it should be have been someone in STEM, but this is how things go.

Imagine you are stationary in space.. Your cosmic horizon acts like a giant, inverted black hole, providing a constant "pull energy", 10^69J, that stretches space outward in every direction. When you are at rest, this pull is perfectly symmetrical.



But there is a fundamental law: Total Horizon Energy must be conserved.

Say Alice's ship is accelerating toward a distant star. When Alice "moves," she is actually choosing a distant patch of space and matching its recessional velocity. In that direction, the natural pull of her horizon would drop because she is now "surfing" with the flow. Objects beyond that distant patch now move away from Alice at Hubble's Constant relative to that patch. To prevent this energy deficit of weaker forward recession energy, and ensure the same amount of information crosses her horizon no matter Alice's velocity, her horizon must reorganize space to conserve the total energy of Alice's cosmic horizon.



To keep the total energy constant, the coordinate system in front of her must blue-shift. Objects appear to age more quickly and move behind Alice because Alice has adopted the Dark Energy perspective of her destination.

From the star's perspective, Alice appears stationary because she is matching the recession exactly. She isn't "aging slower"; her clock still ticks at one second per second. She has simply "cleared the cache" of the universe’s past more quickly to satisfy her horizon’s energy quota.



Bob on Earth slips behind Alice's cosmic horizon. The cost is permanent. As Alice shifts her perspective, other observers will notice her causal boundary moves with her. Eventually, her old home and Bob slips behind her horizon and is erased from her universe forever.



To move is to overcome recession. To stand still is to be balanced against the universe's own stretching fabric.

Dosen2 sekarang, spesial membuat sesuatu yg mudah terlihat sulit, makanya mereka menyukai Mekanika kuantum, Mengapa? Karena Mekanika Kuantum tidak disukai Mahasiswa pintar karena mereka tidak tahu cara menjelaskan nya kepada orang Bodoh dengan cara yang paling sederhana sekalipun. Mereka ini hasil didikan Guru yg di masa lalu gagal dibuat paham dgn cara paling sederhana, mereka hanya paham dengan jalan2 yg sulit, sedangkan metode paling mudah sengaja tidak diajarkan, supaya orang tetap menganggap Mekanika Kuantum itu yang tersulit dari yang paling sulit😂

§ 6. Einstein's Electrodynamics (SR)





In Einstein's special relativity paper, "On the Electrodynamics of Moving Bodies" (1905), Einstein stated that the luminiferous ether was "superfluous" (Einstein2, Intro). Maxwell's equations are used to represent the formation of an electromagnetic wave without an ether where the oscillating electric field forms a magnetic field but Maxwell's equations are analogies since a magnet or varying capacitor cannot oscillate at the frequency of light which invalidates Maxwell’s theory; consequently, Einstein supported Maxwell's theory using spacetime.



"§ 6. Transformation of the Maxwell-Hertz equations for empty space. On the nature of the electromotive forces that arise upon motion in a magnetic field.



Let the Maxwell-Hertz equations for empty space be valid for the system at rest K, so that we have









dX/dt = dN/dy - dM/dz.................................................24







dY/dt = dL/dz - dN/dx..................................................25







dZ/dt = dM/dx - dL/dy..................................................26









......................................................................................







dL/dt = dY/dz - dZ/dy...................................................27







dM/dt = dZ/dx - dX/dz..................................................28







dN/dt = dX/dy - dY/dx..................................................29











where (X,Y,Z) denotes the vector of the electric force, and (L,M,N) that of the magnetic force." (Einstein2, § 6).











β = 1/(1 - v2/c2)1/2........................................................30











Applying equation 30 to the coordinate system of Maxwell's equations,




"X' = X.......................... L' = L......................................31a,b





Y' = β[Y - (v/c)N]......... M'= β[M + (v/c)Z].....................32a,b





Z' = β[Z + (v/c)M],........N' = β[N - (v/c)Y]"....................33a,b









(Einstein2, § 6). Einstein's spacetime β = 1/(1 - v2/c2)1/2 become undefine for light (v = c) which invalidates Einstein's special relativity.

1:10:16

46:56

helpful 🙏❤

22:00 He is rather wrong here in the concept of clock synchronisation. "Two clocks are synchronous if rays emitted from them arrive at the midpoint at the same time. However I who is moving, say, those clocks are not synchronous because light from them does not reach me at the same time".

If we were god, we could probably know the axis of time and axis of spaces would have swiveled out of measures of time and space simultaneously

Special Relativity can be understood from the perspective of simple trigonometry.

Velocity, relative motion, may be modelled as an angular displacement between reference frames, where the sine of the angle is set equal to v/c. Then the Lorentz correction factor becomes the cosine of the angle. The frames are rotated relative to one another in the plane defined by the time axis and the axis of relative motion. Length contraction and time dilation are only apparent, as viewed from the adjacent frame.

Using these same relationships, one finds that the equations of velocity transformation (when considering three reference frames with relative motion along a common axis)..exactly parallel the equations of spherical trigonometry. Fascinating. One would ponder a guess that a four-dimensional spherical trigonometry would be needed to analyze the relative motion of four reference frames along a common axis.

The mass-energy equation is often seen as a spectacular success of the Theory of Relativity, however it is really a consequence of Maxwell's Theory of Electromagnetic Phenomena which implies that mv=E/c. (E=energy, m=mass v=velocity, c=the speed of light).  Letting v=c, clearly yields E=mc^2.  Maxwell's Theory suffered from the totally unnecessary postulate of there being a fixed ether through which objects move.  In Reference Frame Dependent Theory, or Special Galilean Invariance, for which information has been available online for at least 7 years - though hard to find and apparently totally ignored - light waves are posited to be a property belonging separately to each independent reference frame, so that all light waves would travel with velocity c relative to anyone who observes them, but need not travel with this velocity relative to others or to their source.  An observer traveling with velocity v towards a light source would see a light wave which had left with velocity c-v relative to that source.  It might seem strange that a light wave would only be observable by someone towards whom it is traveling with this velocity c, and not exist for others, but this does not seem to be inconsistent with what holds for electromagnetic phenomena in general. An observer who is stationary relative to an electric charge should observe no magnetic field resulting from the charge, but another observer in the same essential location who is in motion relative to the charge would observe a magnetic field as a result of the relative motion.  A light wave can be described as nothing other than a series of changing electric and magnetic fields, so a light wave visible to an observer in one reference frame would not, it would seem, need to be the same as one that could be observed by someone in another.  Two light waves emanating from a single source in the same direction might therefore travel with different velocities relative to each other, each existing only in their own reference frame.

This video is very informative. Einstein’s second postulate is miss quoted in this video. Einstein’s second postulate states that light travels at a constant velocity c in a vacuum relative to a stationary inertial frame and that the constant velocity c is independent of the motion of the light source.

The second postulate does not say the speed of light is constant relative to a moving inertial frame as implied in the video.

This means that a ray of light emitted from a moving source will move away from that source at a relative velocity equal to the speed of light (c) minus the velocity (v) of the moving source or c-v. The light ray will also be blue shifted as it is emitted by the moving source. The light ray velocity, relative to a stationary inertial frame will be constant at c when measured properly in a moving frame. The proven way to measure the true speed of light in a moving inertial frame is a two way measurement method. The two way method consists of reflecting a light beam off a mirror and back to the source. This method eliminates the velocity of the moving inertial frame and produces the true speed of light c. The simplified formula is (c-v+c+v)/2=2c/2=c.

Knowing this, a space time diagram depicts a ray of light moving at 45 degrees relative to the time axis and only into the future. This is a one way motion of light and is only a constant velocity of c when viewed from the perspective of a stationary observer. If the spacetime diagram is rotated away from the frame of reference of a stationary observer the light line is no longer the true speed of light but becomes a relative velocity of the light beam to the speed of the moving frame and will not be 45 degrees relative to the time axis.

To clarify the point, the 45 degree angle between the time axis and the light line is only correct if the spacetime diagram is viewed from the perspective of a stationary observer.

A simple way to keep this clear is just to consider that a light beam only moves in a stationary inertial frame as soon as it is emitted from any stationary or moving source. A moving inertial frame is then superimposed onto of the stationary inertial frame. The moving inertial frame has no effect on the constant speed of light c in the stationary inertial frame and the relative velocity between the two inertial frames can be identified.

Thank you Stanford University.

You guys know skandha??
He is your topper in cracking and hacking.
He also got the highest package of the decade offer (don't know what that is but yeah)

Can someone tell me what are the things I need to learn before studying this, it is quite difficult for me as of now

When finding that a light ray can connect two points and have the proper time 0, he writes that -t = x is the light ray going in the other direction, but isn't it -x = t? Simply the coordinates aren't -t and x. And since x cannot be greater than t, x = -t wouldn't make any sense either. Have I misunderstood something?

1:57:15 - I read and answer a lot of questions on Quora, and I'm just astounded at how common it seems to be for people to have some kind of a niggling desire to "tear Einstein down." I don't know if they're just intimidated by the fact that truly brilliant people exist, or if it's because he was Jewish, or what, but it's surprisingly common. I think it's ridiculous. Even a cursory knowledge of science history makes it clear that yes, Einstein really was that good. He deserves every bit of the credit he's given. He was truly, truly exceptional.

1:29:49 - You have to be very careful thinking about the acceleration as "the cause" of the twin situation. That's not quite right. It is possible to have the twin that stays at home wiggle back and forth a small distance during the experiment such that he or she experiences all of the same TOTAL acceleration that the traveling twin does - that will not change the outcome of the experiment. The outcome is more global than that, and really involves planes of simultaneity.

The upshot is that during both constant velocity legs of the trip the twins are symmetrical, and both see the other's clock running more slowly. But, when the traveling twin changes direction, his lines of constant time change, and that causes his perception of "now" for the stationary twin to "leap over" (or race rapidly across, if the turn-around is gradual) a bunch of the stationary twin's world line. That's how the stationary twin winds up older, and the acceleration (the change of direction) AND the distance between the twins affects how big a jump that is.

There is no real "paradox" here - it all makes perfect sense, and the best way to see it is to just religiously trust the math - it gives you the right ansnwer.

Thank you professor,...I don't know any physics but, Also it call my attention the velocity poison spreads in different situations and it's influence in different species....how relative is it for us to understand

Awsome 🔥 course everything is the same for relativity...I wonder how the velocity of our planet in the center Ecuador affects the the other sections of the planet

God I only wish my professors could explain and teach at half the proficiency that Prof. Susskind does.

Excellent lecture. Just one minor correction:

1:42:02 It's NOT "the square of the difference" but the difference of the squares (of the time interval and the space interval, respectively).

🖖🤓

You at the back of the class can you please raise your hand if you’re the monomyth

I'm a freshman undergraduate student. There would be no way I was going to pass the first semester exams if not for lectures on physics from mit and Stanford. In my university, they barely explain this stuff and expect you to already know/understand it anyway

Seriously - Stanford can do better than this.

Great lecture. What I really miss in all those lectures are examples. Examples with numbers. The course would take twice as much time, but the number of people who understood would increase much more. I know it; I do lectures on much less complicated technical subjects, and as soon as you come from theoretical equations to practical use, it can be seen how many students get enlightened. Covariant and contravariant vector, show the transformations - 2 dimensions would be enough.

I can't honestly tell if he's a Jew or not... 😯😯🙃🙃

Clark David Brown Steven Hernandez Robert

Beautiful lecture ❤