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Einstein thought it was best to understand Relativity intuitively rather than focusing on the math. The best way to understand dilation/gamma/y is to imagine a spaceship traveling at a constant acceleration rate. When the ship reaches 50% light speed, as viewed from an Earthbound observer with a magically powerful telescope, it would appear normal because as a dilation graph shows nothing has changed at that point. When the ship reaches 75% light speed it would appear fuzzy because as the graph shows relativistic effects would be noticeable at that point. When the ship reaches 99% light speed it would not be visible because every aspect of its existence would be smeared through spacetime relative to an Earthbound observer, not onto itself.

Einstein thought it was best to understand Relativity intuitively rather than focusing on the math. The best way to understand dilation/gamma/y is to imagine a spaceship traveling at a constant acceleration rate. When the ship reaches 50% light speed, as viewed from an Earthbound observer with a magically powerful telescope, it would appear normal because as the graph shows nothing has changed at that point. When the ship reaches 75% light speed it would appear fuzzy because as the graph shows relativistic effects would be noticeable at that point. When the ship reaches 99% light speed it would not be visible because every aspect of its existence would be smeared through spacetime relative to an Earthbound observer, not onto itself. This is the state of mass in our galactic center. It's not just there, it's everywhere. It is the "missing mass" needed to explain galaxy rotation curves.

8:10 why???

thank you!! you made this really easy to understand :)

The photon never takes both paths.

Hi James, I really enjoy your video. You explain topics that could generally be difficult and made them easier to understand. Thank you for that. I have a question. In this video at timestamp 3:18 you mention a logical contradiction would occur if length contradiction did not happen. Can you tell when what that contradiction would be?

Again excellent! Thank you. ❤

Excellent video! Very clear explanation. Thank you ❤

I am not sure if this is correct. What you're referring to is Euler's Theorem en.wikipedia.org/wiki/Euler%27s_rotation_theorem, not Chasles' Theorem en.wikipedia.org/wiki/Chasles%27_theorem_(kinematics). Chasles' Theorem is much deeper and says that any motion can be described as a screw motion (translation along an axis and rotation around that SAME axis).

Total nonsense. Einstein says that if there are two bolts of lightning, one ahead of a moving train and one behind, at equal distances from the train, and simultaneous in the frame of reference of the train track, an observer at the middle of the train will see the flash of lightning ahead of the train first because the train is "rushing toward" the front bolt of lightning, so the light does not have to travel as far. This contradicts everything Einstein said previously about frames of reference. If we consider what happens from the frame of reference of the train, the train is not moving, and the track is moving beneath the train. If the lightning strikes ahead and behind the train at equal distances from the train. it takes the same amount of time for light from each bolt of lightning to reach the observer. If distances do not contract, which is what the Galilean transformation equations have always said, then the observer on the train sees a photon from each bolt of lightning at the same time, the same as an observer on the ground because in his frame of reference, the bolts of lightning are just moving sources of light, and Einstein already said that movement of a source of light does not affect the time an observer will see the light. Whether the light is moving toward or away from the observer, all photons emitted after the first one will reach the observer after the first one. The only thing that matters is the distance between the point where the photon is emitted and the point where it is observed in a frame of reference at the time the photon is emitted.

best explanation

I think that these videos are incredibly useful and underrated. Thank you so much for such high-quality content!

Hasn't the quantum eraser been debunked? It is my understanding that the waveform collapses when creating the entangled pair at the non-linear crystal.... thereby showing no interference pattern

This series is the best explanation of interferometers that I have ever found. Great work!

Thanks for this video. It's really good! How can we further "find a condition under which the bead the bead can descend from an initial height h with an initial speed of zero and ultimately reach the origin"?

Excellent explanation.

If the two bodies are in a central potential why does the potential U only depend on the distance r between the two bodies? Shouldn't the individual distances between particle and origin of the central potential also be considered? I would think that the total potential is U = U_12(r) + U(r_1) + U(r_2) with U_12 being the potential due to the two mass particles and U being the central potential.

Thanks This was helpful

Thank you for your explanation, I think I've nearly understood what's going on. I'm a little unsure with the vertical bar notation and "evaluating at the limits". Is it the same thing as taking the definite integral of F(x) from a (lower bound) to b (upper bound) and computing F(b)-F(a)?

excellent video

Excellent explanation! Thanks!

OMG your videos are great! Thank you sooo much!!!

Thank you!!

very helpful thanks! I too didn't understand how you derived the w squared from the second derivative?

Nice video and a good point is made at the end of the video - it is of course a fallacy that the 'path' information can be used in reasoning before measurements are made. In Quantum Mechanics only the wave function exists prior to a measurement. So the concept of a 'path' can't be used before a measurement takes place, and even then it may just be impossible to determine which path a photon 'may have taken' before the measurement is made. Before a measurement takes place there is NO classical reality. As it is only meaningful to talk about the wave function before measurements are made, the model needs to be set up as follows : At the first beam splitter BS1 the system input wave function F becomes a superposition of Fh + Fv. If no phase changes etc. occur at the mirrors then 'roughly' Fh becomes Fv, and Fv becomes Fh, so after the mirrors the new wave function is unchanged F' = Fv + Fh. So this is the incoming system wave function at the location BS2. If BS2 is not there even though only one Det y or Det x 'clicks' to say a photon was detected there, it tells NOTHING about the 'path taken' before getting to the detector that 'clicked'. Prior to the click the wave function was F' = Fh + Fv and by the way the experiment is set up we had NO WAY of determining what happened before the 'click'. To try to 'back calculate' whether a particular path was followed based upon which detector 'clicked' is TOTALLY MEANINGLESS and impossible to do using Quantum Mechanics. So in the Quasar example the light wave function was in a superposition prior to detection at the Earth. As a result it is impossible to say whether a particular classical path was followed, since only a wave function existed before reaching the Earth and indeed no classical path would be followed. Indeed the delayed choice experiment is a sort of Bell's EPR experiment which shows that classical reality DOES NOT EXIST prior to a measurement taking place. What constitutes a 'measurement' is an open problem in Quantum Mechanics, since Quantum Mechanics theory does not say what a measurement is. Now that is a really thorny question.

Hai sir,i have doubts on some problems..i need some guidance for that...i would like to ask my problems towards lagrangian and how can I post my doubts ,show me some way to contact u

Beautifully concise and elucidating. Thank you.

Super great videos. I missed where the w squared = double derivative of eff potential divided by mu came from?

what textbook is this from? thanks

I made this video ruclips.net/video/o6r4ZWw4bHE/видео.html suggesting that the beams could affect the experiment and your video confirms on 13:00, please let me know. Thanks

Awesome, thank you. As a matter of interest, if r can be completely specified with r and r-hat, why do we even need phi?

If there exist a beautiful love story on the universe it would between symmetry and conserved quantities....The way You explained from the scratch was beautiful

This is a seriously great explanation!

Thank you so much! Can you please recommend more materials on the different experiments on this theme?

what would happen when the time period of radial oscillation = 1/2* time period of circular orbit? Im guessing we would divide the circle at pi and then draw one cycle in each half...

In the last experiment I don't understand how clean is this idea with the gate? For how long this gate is open and does the length of paths D1-CC, Dr-CC and Dt-CC matters?

Thank you for this course! Very nice explanation

Best video on this theme ever! Thank you

thanks prof

James, please tell me you don't actually believe all this nonsense, do you? spacetime, time dilation.... wow, such moronic drivel.

ahhh it is so hard /...

I wonder how it really is in real actual life. I wonder, I just wonder if people really think about that. Everybody just draws a line, train, up and down with some makeshift light or whatever.... Has anybody ever seen such a thing in real life. I sure haven't. Am I the only person who asks this. I don't see anybody ever ask it. The chances are nobody cares enough to ask. Another thing is, why in the world everybody use the same example? Isn't there thousands of other examples for pete's sake. And why does everybody show the object moving away? Don't objects ever come towards you in this world? I guess not. I wonder why no one can explain these things just by simply talking instead of some paper and pen or chalk boards..... that is not what it actually is.. so what is going on?

Thanks! I was looking for this example!

This helped me get my head around degrees of freedom and how to define them, thanks!

Brilliant. Thank you.

Thanks sir ! Was going through my last sem's curriculum, found Chasles Theorem, thought I forgot this Thanks a ton for the explanation !

Do you have an answer for your last question about there being a torque from non-zero angular momentum to zero? I can understand that the maths cross product of vectors r x f can explain it but intuitively I am finding this difficult to comprehend. It's almost as if the gravitational force of the Star is pulling the planet towards origin 'O' for a section of its orbit than pulling it away as the planet moves closer to 'O'.

Einstein put in the "stationary" system, but what is the stationary system stationary to? The stationary system is stationary to the stationary observer (the stationary observer is in the stationary system), and the stationary observer is stationary to the stationary system. Stationary = rest, but what is the rest-system at rest to? The rest-system is at rest to the rest-observer (rest-observer is in the rest-system), and the rest-observer is at rest to the rest-system. So we end up with nonsense.

Excellent work sir, you are actually teaching the stuff unlike the plethora of relativity videos that just make gimmiky statements and state things factually with no real explanation.

I actually understood that, thanks!