Relativity - Chapter 5 of 6

An in-depth look at the ground-breaking discoveries of Albert Einstein and the implications within our physical world. (6 chapters total!)

Category:

Science & Technology

Tags:

• Physics
• General
• Relativity
• Einstein
• Equivalence
• Principle
• Gravity
• Nuclear
• Power

[pwned222222222222222]

Does gravity slow down light or just make it take a longer path. ie would the light near a black hole orbit around it or simply hover inside the event horizon, not able to escape its gravitational attraction.

[cassiopeiaproject]

@pwned222222222222222 Interpreting the equations regarding the space aground a black hole allows us some latitude in the verbal descriptions of light behavior in this weird environment - but "hover" is not a word that brings to mind an acceptable mental image. It would be better to imagine that light bends with the space and turns back down toward the singularity or that its wavelength stretches to infinity as it tries to escape.

[cassiopeiaproject]

@pwned222222222222222 There are no finite, continuous geodesics around a black hole that trace a path from inside the event horizon to outside the event horizon, and since light travels on geodesics, there are no paths for light to follow that allow it to escape.

[cramis1]

My block has always understanding how the idea of gravity being the same as an accelerating frame leads to a a curved space-time? What about this fact of being in an accelerated frame or within gravity, means objects bend space-time and therefore attract other objects?

[cassiopeiaproject]

@cramis1 Picture this... You are in an rocket ship away from all gravity, and like the one in the video, it is accelerating in your "upward direction". If some "stationary" person outside the rocket ship shines a beam of light horizontally through the ship, you will see the shape of the beam as a curve.

[cassiopeiaproject]

@cramis1 You will see it enter the ship from one side, and it will curve toward the floor before it exits the other side. If light travels in a straight line -- or a geodesic of the space -- then your interpretation must be that space is curved. Since gravity does this to light as well, gravity must curve the space..

[lattask8er]

But does gravity only work if the space is distorted by an object, so is it the mass of the object that distorts space, that causes the presence of gravity?

[CassiopeiaMember]

@Bighillwilkl You are correct. When the ship is no longer accelerating, the person on board would see the light beam traveling in a straight line.

[Bighillwilkl]

@cassiopeiaproject (continued from below. I hate this backwards forum layout.) yet has been there on the event horizon of the black hole or wherever it was absorbed ever since it was emitted, in it's own frame. Looks to me like a hypothetical spaceman, if he survived all the stretching and radiation, would never know he had passed through the event horizon. He could still see out, right? Oh, and infinitely small is not zero. There must be a divide by zero somewhere, this can't be right.

[Bighillwilkl]

@cassiopeiaproject I'm wondering if "hover" isn't actually a pretty good word, from the photon's frame of reference. I'm probably totally wrong, but doesn't time dilate as relativistic speeds are approached? So, if time dilation approaches infinity near c, wouldn't time T actually = 0.00 at c ? In other words, wouldn't a photon travelling at speed c experience zero time? Or is it just an infinitely small time? The way my math works out, the photon has never arrived, but

[Bighillwilkl]

Oh, wait, I think I got it. Without acceleration the forward shift / blue shift would be constant, and the beam would appear straight, right? Sorry, I thought about that for two hours before I posted, and that idea occurred to me just after I hit "post." If it is right. What a great series. Thanks!

[Bighillwilkl]

But suppose your supership had already got you into the near light speed realm, and you were in an inertial frame and no longer accelerating? You would feel no gravity-like light-bending force applied. Would you still see a curved light beam? Sorry, I don't know the math, or I might be able to see it. Thanks.