Classroom Aid - Equivalence Principle xx

[martijn]

Fantastic explanation with exactly the visuals I was looking for! Thanks so much David!

[walterbrownstone]

Acceleration is equivalent to acceleration. Wow brilliant, Einstein.

[AlpharderCodes]

Thank you, excellent and helpful visualisation! Einstein was surely genius cuz its VERY counterintuitive.

[phenomenalphysics]

thank you thank you so much!❤️❤️❤️❤️❤️❤️❤️ I see no other video explaining this chapter of Einstein special and general theory of relativity! thank you it's been a great favour!❤️

[ASCENSiON]

0:44 you meant to say here constant acceleration.

[atheistaetherist]

Re Einstein’s silly elevator/chest gedanken for supposed equivalence.
1. Hanging wts will hang parallel in accel, but will converge if in gravity.
2. Clocks will tick at same rate in accel, but will tick differently if at different altitudes if in gravity.
3. Photons crossing the room will all remain horizontal in accel, even tho the ray of light curves down, but photons will not remain horizontal in gravity, they will have a slope parallel to the curved traject if in gravity.

Re 3. Einstein’s elevator/chest gedanken for the equivalence of a curving ray of light in accel & in gravity ignores this lack of equivalence. If we apply Einstein’s gedanken to the bending of light passing a star then no photon passing a star would ever fall below the mid-line of the star. Hence there would never be a focus, hence there could never be an einstein ring, or even a part-ring.

Every one of Einstein’s gedankens is wrong. His prediction of the doubled bending of light passing the Sun is a lucky guess. Likewise his prediction of rings. Likewise his prediction of Shapiro Delay. None of these are a legitimate prediction of any of his gedankens.

Re 2. I should add that all kinds of clocks must be affected differently by altitude & by velocity. Tests show that some atomic clocks behave nearnuff as per GTR. But we will find that GTR does not apply for most kinds of clocks, eg tuning fork & balance wheel clocks.

[ManojKumar-iiyd]

In Gravity for instance ur hands will feel the force, but not in case of the Elevator acceleration. For human body they surely are different. There will be more pain in joints in case of acclerating Elevator....i think.

[gromajor]

excellent explanation. congrats. 👍 it helps vizualize a lot.

[aniruddhachakrabortyindia]

Does that mean we see light rays bend while standing on earth?

[tomscott]

excellent. at 3:08, it might have been clearer if "outside" was inserted under the wording of both frames on the right.

[aveersingh]

So, how do we account for the fact that we can differentiate between a rocket ship accelarating upward and being at rest on the Earth as follows-
By shining a beam of light in the accelerating rocket ship, we find from inside it that light "bends" as in it has a lower height when it touches the elevator.
But, Shining a beam of light on the Earth doesnt result so, and that we receive the same level of light when it hits the wall of our house or lab, and DOESN'T "bend"?

[ThomasJr]

I have this question. Relative to the outside observer, all remains the same, the light path is a straight line. From the point of view of the guy inside the elevator, that's when strange things happen, because as crazy as it seems the photon is not dragged up like the rest of the things inside the elevator. Why is that? Since the photon seems to make a curve inside the elevator per the observer in the elevator, its trajectory is longer than when the elevator is at rest.

[ThomasJr]

*I am very confused. I thought the laws of physics should only be equal for inertial reference frames. Now this seems to be saying that the laws of Physics are the same for all reference frames??? Even reference frames with different accelerations??*

[walker]

So on Earth, the ball falls to the ground because the Earth is moving upwards, but upwards is one direction. What if you are on the other side of the planet?

[siddharthsrivastava]

Hello sir, I'd like to say that in the video in 02:25, you have only shown what the outer observer sees when the elevator has moved up the height equal to the original distance of the ball from the elevator. What happens if the elevator keeps moving even after that? Will the outer observer simply say that the elevator is carrying the ball upwards?

[Guustaaf]

At 45 sec "starts accelerating at a constant velocity". Acceleration means change in velocity. You should correct this.

[ThomasJr]

*Hey Dr. Butler, but the equivalence principle is not exact, right? As there are the tidal forces (on Earth the pull on the feet is stronger than the pull on the head). So this principle is only approximate, and the person in the elevator in principle can tell that his feet has the same "a" as his head (hence equal forces), whereas the person on Earth has different forces at his feet and at his head.*

[gabrielorsi]

will the distance between the walls of the accelerating elevator stay the same? because light is taking a longer path, and its velocity must be constant to both observers, must distance change or time?

[fredashay]

Mr. Kotter! Mr. Kotter!!
I'd be able to tell the difference!!!
The person who stayed in the "elevator" on Earth will be older than the person who traveled in the "elevator" through space.

#ItchyFeet

[GuyusSeralius]

I enjoyed this video presentation. But I would think one could determine whether or not he or she were in a box resting within Earth's gravitational field or in a box being accelerated in space simply by dropping two objects. Drop the first from 1 meter high and the second from 2 meters high. In a planet's gravitational field, the first object should strike the floor in less time compared to the time it takes the second object to traverse a meter, since objects further apart have less attractive force. If you did the same within an accelerated box in space, both objects would traverse a meter in the same amount of time regardless of where they were released--right?