Why does gravity bend light even without mass?

In this video, we rediscover Einstein's equivalence principle. It solves one of the biggest mysteries of Newtonian physics - why gravitational mass = inertial mass. But in doing so, Einstein completely reinvents the ideas of gravity. Starting with gravity being an illusion. A mere side effect of the 'ground' accelerating 'upwards'.

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This video is sponsored by squarespace

[Mahesh_Shenoy]

PS: There are quite a few comments about how gravity doesn’t bend light, but it bends spacetime and light just follows it. Well, If we didn’t know this already, how would we go from special relativity + Newtonian gravity to rediscover space time curvature (and in the process, gain a deeper insight into it)? That’s the question this video series is trying to answer!

PPS: Yes, I should have used limit m->0. If not show it, at least mention it.

[jcole]

Gravity doesn't change light, it changes space, light travels in a straight line through space, if space is curved, the light curves with it. In a straight line.

[Dinoplank]

Please do a video where you show off all of your joke t-shirts and explain the jokes.

[scienceisdope]

I finally understand the equivalence principle!
I still have some questions but like you said, I'll wait till the next episode of dragon ba... I mean of float head physics...

[donutwindy]

Newton pours water into a glass. Einstein moves the glass up to meet the water.

[profane]

I'm so happy I stumbled upon your channel. You do such a great job of explaining things in a way in which it's easily - about as easy as physics can be anyway :) - digestible.

Great stuff, thanks!

Edit: and entertaining!!

[raymondmeyers]

Gravity doesn't bend light. It bends space and time. Light simply follows that curvature.

[sgiri]

Its like listening to the story. It does not seems like watching the educational videos. This is because of mahesh sir incredible talent. Who all agrees ?

[Yezpahr]

That rollover to the sponsor message...

Infinite pricelessness achieved.

[varsha_]

Mahesh is not pregnant, but he never fails to deliver (his insights)😂

[JerryPenna]

Save yourself 17 minutes: gravity bends the fabric of space not light itself. You’re welcome! 😉

[astronomers]

Wow one of if not the best explanation. Einstein would be so proud of you. Please don't change and become as complex as the other physicist

[popquizzz]

Simply stated; Gravity warps Spacetime. Light made up of massless photons will move in a straight line unless acted upon. Light is just moving in that straight path of warped spacetime and from our frame of reference is perceived to be being bent around a large body or gravitational mass. We know Dark Matter can warp spacetime, but why doesn't Dark Energy? If mass and energy are basically the same, i.e., E=MC2m, why doesn't Dark Energy warp spacetime or does it? Is this the reason for the difference in measurements of the expansion rate of the Universe? The aptly named: Crisis in Cosmology?

[fairworld]

Gravity bends space not light. So what we are observing is light traveling trough bended space

[tg-spgamer]

Why gravity is independent of mass ??? If gravity is indepent of mass than concept of momentum And Here in the formula you are taking a = g how it explains that gravity is independent of

[rize]

Zooming out - there is another person on the other side of the planet, where ground accelerates "up" (which is other direction for our first elevator guy). So planet accelerates in all directions at once. And since it is "impossible" it means that it is not a planet moving in all direction but it's space moving into planet from all directions :D

[jonbold]

"It's not a real force." LMAO!

[rajanvenkatesh]

I quite like the reference to good old Newtonian physics.. the mass or its absence not making a difference to gravitational fall is a good thought-provoking beginning to this video.
I also recall another video of yours where it was the Newtonian concept of relativity (of uniform motion) that Einstein used to figure out the constancy of c (speed of light or causality).
I was in college before computers were born.. I am slightly partial to things classical - physics, art or music!

[turningnull]

Idk human race should know something called "Time-Space radiaction" 😏😏 for essencial's certain waveform as you called "matter"

[DrDeuteron]

So when you do Coriolis/Centrifugal forces in Newtonian mechanics, all that matters is inertial mass: there is no gravitational mass in the problem, its your choice of "moving" spatial coordinates... All of gravitation is the same...it's a choice of "moving" spacetime coordinates.