Dear prof Brian, here is my Question: if a clock is not a cyclical motion device (as used in special relativity), how can otherwise can be?

How can be the clock defined different from a cyclical motion device?

Hello sir, pardon my curiosity but what are you working on with respect to your field of study these days?

@@mahadlodhi pretty sure it's string theory calculations!

Sir, Could we say rest mass is invariant ?

I'd like to think he's contributed more.

@@nickbros If you're talking about him educating more people about science then I'd 100% agree. If you believe he's done more for science in general compared to Einstein, well... No.

maybe the wagon was really long ? did you even watch the video ? ;)

I mentioned the first two in the first video

These are all things. What is the idea you have? Or is the idea to write these 3 things together?

Newton seriously?

Don't be repetitive ;-))

Yes, but does he know how to make guacamole?

@@aaronnatera3685 that should be the next question 🤔😂

If the assumption is that the moving clock is travelling at a constant rate, then by Pythagoras, the tick and tock will be equal. why would there be an asymmetry? You would therefore be saying that the speed of light in one direction, the Tick is different to the speed in the Tock direction, as measured by the static observer. Which directly contradicts Special Relativity.

surely the length contraction applies equally in both directions so can be disregarded?

I figured that should then be the case, but to be exact, one shoul have mentioned that L is in fact L corrected with gamma

The signal from the perspective of someone outside the train will see it on because from the perspective of someone outside the Train the detector only turns on if the signals come at different times.

XD thats a good one

being from the future

In general, one cannot claim to be the first, as someone else in a different inertial frame can also claim to be the first, and it all depends on your point of view!

He hasn't used the Lorentz contraction. He has taken the derived equation LV/C^2-V^2, divided by C^2 and done a little bit of algebraic manipulation.

The photons, once left the light bulb, travel at a constant speed regardless how fast the train is moving. It is indeed true that the photons travel a short distance to reach the forward facing president. But the observer in the train do not get to see it immediately. It takes time for the photons bounced back from the forwarding-facing president and their pen to travel to the eyes of the observer in the train. Now don’t forget that the observer is moving forward with the train, so these photons will have to play catch-up to the observer, and it will take more time than if the observer was stationary. Now if you consider the round-trip, the effects cancel out. So somebody standing equally far from the two presidents in the training will end up seeing the signing events at the same time. To other people in the train who are closer to one president than another, they would SEE the events in different orders. In the extreme case, to either of the president, they’d both see themselves signing first. I think these details are omitted in the video, but it is totally true that observers won’t agree on the order of events depending on their position and frame of reference.

I found this wall of text to related question; "Are moving clocks really running at different rhythms just because of velocity?": Well of course they do, there are 2 effects, one due to gravity and one due to speed.Considering for instance the GPS satellites, the clocks onboard the GPS satellites experiences relativistic shifts, which have both a constant and time varying components. This constant component is compensated for by introducing a fixed offset, which lowers the frequency of the on-board oscillator. The fact that there is some orbital eccentricity and the higher order terms (quadropole) of the Earth’s gravity field are primarily responsible for the components that vary with time. For instance, if two clocks are located on an equipotential surface, the rates of the clocks will be the same. If however one clock is moved to a height of 1 km, their rates would differ by about 1 x10^-13. Earth’s quadrupole’s effect on the potential at the GPS satellite is approximately one part in 10^14 , so in the case of the potential at the height of the GPS satellite, the contribution of the quadrupole can be ignored in most cases (GPS orbits are high enough to be nearly Keplerian); there is also no centrifugal component so that the gravitational potential at the GPS satellite can be easily calculated.The total gravitational frequency shift of the clock onboard the GPS satellite can then be calculated as 45.688 microseconds per day. If you ignored this, you would have a one way navigational error of 13.697 km per day. Secondly when we consider the speed of a GPS satellite, (~3874 m/s), Einstein's special theory of relativity needs to be applied. The time dilation effect causes the GPS satellite to appear to run slow by about 7 microseconds per day. The GPS satellite clocks are adjusted for three constant rate corrections before launching them into orbit, the satellite clock has a higher frequency in orbit than on the ground (read geoid, where the clock frequency should be 10.23 MHz) and its proper frequency is therefore reduced to 10.229 999 995 43 Mhz. So the nett effect is that between the faster clock in the weaker gravity field due to orbital height, and the slower clock due to the clock's in orbit speed, the gravity effect wins. One can calculate this very accurately, and it works perfectly, otherwise we would not have sub-cm accuracy in positioning using geodetic quality GPS receivers.