Astronomy - General Relativity (3 of 17) What is the Equivalence Principle?

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We will learn The Equivalence Principle in 3 examples:
1) The observers can not tell the difference of playing volleyball on Earth or in a spaceship where accelerating=gravity.
2) A super-ball will behave the same way whether on Earth or in a spaceship where accelerating=gravity.
3) Light will “bounce” back and forth downwards between 2 perfect vertical mirrors in a spaceship where accelerating=gravity.

Next video in this series can be seen at:

[tushardubey]

Sir I'm a PhD student and a lecturer but I can't explain like you.thanks 😊😊😊

[mehrabhossain]

Sir you explained this so simply.
I was beginning to lose my love for physics.
This just got it back.
Thanks so much

[MoMocrafterable]

I understood the video, but I have a question. Say the spaceship is accelerating downward at 9.81 m/s^2, the light would seem to travel upward since the hole which it came through would be moving down from its initial position. So the object/light would seem to accelerate upward due to the spaceship moving down. This is in essence relative. So hypothetically, if the earth was accelerating upward at g, and the same experiment with mirrors was done on earth, the light would not change its vertical displacement since the upward and downward accelerations would “cancel”. Correct?

[johntakolander]

There is a HUGE mistake here: The gravitational field has a MEASURABLE gradient. The best gravimeter of today would easily fit in a larger goods elevator and it can detect a height difference caused by the gradient measured in centimeters. We have one here in Finland and those instruments are also used in modern submarines when moving in underwater canyons so that they don`t collide with the walls of the canyons (article some years ago in Scientific American.

[foxhound]

The interesting thing about this, as gravity is described as the acceleration of the frame, standing on earth can not be an actual physical acceleration, the two sides of the earth would be accelerating in opposite directions! Since the earth is not tearing itself apart, this acceleration of the “frame” must be temporal. In accelerating space ship, time runs slower at the bottom of the space ship vs the top. This “time gradient” associated with an accelerating space ship, is equivalent to the time gradient being near a massive object, as such time dilation is not a side effect of gravity, but is gravity. Professor Van Biezen?
Also, doesn’t a theory tell you why something happens, and a law tells you what happens? As such, since Newton himself did not know what gravity was, but his”law” described what happens. Shouldn’t it correctly be Newton’s law of gravity, not Newton’s theory of gravity?

[mathieubuisson]

Can the spaceship be accelerating at 10m/s^2 forever ? Surely it is quickly going to reach speed close to the speed of light.. what happens then ? is time in the spaceship slowing down relative to an external observer and so inside the spaceship it will feel like it keeps accelerating but to an outside observer the spaceship is not actually accelerating at 10m/s^2 ?

[scottdc]

Those equivalence principles are only analogies, you can simulate the force yes i said force of gravity but that doesnt mean its the same exact thing as gravity as to how its produced. As to Eddington proving general relativity, he didnt prove it, he simply documented that light bends while passing a star. Why it is bending is only an assumption if applying it to GR.

[Zamicol]

Thanks for the video! The only thing that could make it better would be a math derivation showing GR time dilation in a gravitational field.

[beyoufirst]

Sir want to ask question from u about black hole...🙋
Sir, space and time gets twist at the centre of black hole, so sir is it really possible that if we can, I know it can't but if we assume that we can escape from its centre .so there is any possibility of any other kind of world out their like some people
2- And sir what is the difference between a white hole and a black hole.
Plz do answer sir your video always helped me a lot and that's why I want to know more from you as u explain each and everything so perfectly.

[Potassium]

hi professor I have already solve the equivalence principles and I have the answer why inertial mass and gravitational mass the same
I am sure 100% my idea is correct

Where can I pass my article or my papers ? it’s big lot help if you can give an advice

[kimvedros]

So you’re saying that two parallel mirrors and a light beam set up on earth would yield the same result as in the space ship. Hard to fathom.

[tseckwr]

How about if the people in the spaceship bounce back and forth and the ball stands still? Thanks for all your hard work making these highly informative videos.

[sharoonaftab]

serously this guy knows everything and makes me feel like a fool

[naadersafar]

If the ship traveled at v veloccity . is still the light will go down and what is the different ?

[synapticmemoryseepage]

I'm struck that a massless object is pulled by gravity. Gravity and light seem to be dependent on time and motion, but light travels without acceleration. Is this correct? If so, is this a reason light can be pulled by gravity?

[MandolinSunrise]

Thanks again!
I was wondering, did Einstein have help? In 1919 were there any examples of other astronomers who had actually observed and then calculated that light must be bending while passing near massive objects? Maybe clocks weren’t good enough to calculate that.

[aqilshah]

The frame associated with spaceship is inertial or non inertial???... I am confused because inertial frames are unaccelerated frames...

[vgovind]

Great video! A doubt though...as light is travelling at 3×10^8 m/s which is very large compared to the velocity provided by acceleration g, by the time the spaceship moves upwards(so does the hole), shouldn't light be able to get out of the hole?(considering that the other side of the spaceship also moves upward?)..

[peterfred]

How can you or general relativity explain human levitation and the observed propulsion of UFO that show little evidence of rocket exhaust. Why do you not start thinking, as I have done for the last 50 years, that it is not the mass of the sun that attract the planets but the light coming from it. This is a simple notion. Try it out think about it. For more on this notion and five experiments showing how heat and its contrasting opposite "coldness" can actually increase or decrease the weight of a test mass by 5-10 % go to: Peter Fred vixra: 0907.0018.