if light doesn't have wieght then why does it fall into a black hole?

Question

I mean weight is mass correct.

two many good answers.

all theoretical though I suppose.
I'm tempted to go for the e=mc2 answer.
any bribes on 10 points?

Answer 1

Great question. Light goes into a black hole not because light has mass but because the space-time curves into the black hole and there are no other physically realizable paths for light to take. Light takes the shortest possible path through space-time, called a geodesic, which means that when the space-time is severely bent, like near a black hole, it has no choice but to follow the shortest path - it has nothing to do with the mass or lack of mass, of light.

It is not an intuitive concept since we don't perceive this with our senses.

Answer 2

First of all, weight and mass are two completely different constructs. That is why you have different weights on Earth and on the moon—even though you have the same mass. Gravitational forces affects your weight.

Now, on to the question about why does light "fall" into a black hole...

It's all a matter of geometry. It has nothing to do with weight.

Light rays follow geodesics in space-time. Ordinarily, light travels on a straight-line path. However, light follows a curved path if it passes through a strong gravitational field. This is what is meant by "curved space." The bending of the light rays increases as the strength of the gravitational field increases.

A black hole has such an enormous concentration of mass—in such a small radius—that its escape velocity is greater than the velocity of light. So, since nothing can go faster than light, nothing can escape the black hole's gravitational field. Even a beam of light would be pulled back by gravity, and would be unable to escape.

One way to picture this effect of gravity is to imagine a piece of rubber sheeting stretched out. Imagine that you put a heavy ball in the center of the sheet. The weight of the ball will bend the surface of the sheet close to it. This is a two-dimensional picture of what gravity does to space in three dimensions. Now take a little marble and send it rolling from one side of the rubber sheet to the other. Instead of the marble taking a straight path to the other side of the sheet, it will follow the contour of the sheet that is curved by the weight of the ball in the center. This is similar to how the gravitation field created by an object (the ball) affects light (the marble).

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For those of you who like details...

Newton thought that only objects with mass could produce a gravitational force on each other. Applying Newton's theory of gravity, one would conclude that since light has no mass, the force of gravity couldn't affect it.

Einstein discovered that the situation is a bit more complicated than that. First he discovered that gravity is produced by a curved space-time. Then Einstein theorized that the mass and radius of an object (its compactness) actually curves space-time.

Mass is linked to space in a way that physicists today still do not completely understand. However, they realize that the stronger the gravitational field of an object, the more the space around the object is curved. In other words, straight lines are no longer straight if exposed to a strong gravitational field; instead, they are curved.

Space-time is curved in the vicinity of black holes. A black hole is simply a region where the effect on light is so great that light cannot escape the region.

Black holes don't really have solid surfaces as you might be thinking. Black holes have horizons, but that's a region in space, not a solid surface. Those observers who do cross the event horizon of a black hole are constrained to fall toward the center eventually. There simply are not any geodesics that cross the horizon in the outward direction. At the center there is a region of infinite density and zero volume where everything ends up.

Answer 3

A black hole causes a severe curvature of spacetime. A photon of light zipping along at, go figure, the speed of light simply follows that curvature into the black hole's event horizon. Think of driving along in a car along a straight road. You are approaching a hill. Without turning the wheel or pulling back on it, you went up. How'd that happen? Well the earth pushed the car up instead of letting it go through the side of the hill. This is all that happens to a photon. From it's perspective, it is going along in a perfectly straight line through curved space. It just hits a really really sharp curve. This is all the earth does too. It goes along in a straight through spacetime that has been curved by the mass of the Sun causing it to orbit the Sun. Same thing for anything that orbits something else. Everything moves straight, it's spacetime that's gotten bent.

Answer 4

The reason it can't escape a black hole is because General Relativity has shown that gravity can bend the direction that light travels. The stronger the gravitational pull of the object that the light travels near to the more pronounced the angle at which the light ray is seen to bend.

In the case of a black hole the gravitational pull is considered to be infinite so that any light that goes in and tries to escape is bent at a near 180 degree angle because of the intense gravity in the black hole.

In the black hole it's theorized that the singularity actually does emit light, but we can't see it because it's bent to such a degree by the force of gravity that it's path is reversed and it looks similar to the path of a boomerang, coming back toward the singularity.

Answer 5

Hi. It doesn't. It follows a straight line under all conditions. The straight line near a black hole is curved due to the intense gravity. If a photon gets close enough then it goes into 'orbit' at the event horizon. The straight line becomes an ellipse and the photon is trapped in this ellipse. The photon can HIT the black hole, but it doesn't 'fall'.

Answer 6

yeah mass would be correct not weight, and the theory is that a black hole is so massive and has such a huge gravitational field that not even light can escape it. This is because the escape velocity (the minimum velocity required for an object to be released from a force) exceeds the speed of light, and since nothing can go faster than the speed of light, nothing can escape a black hole

i hope that helps!

Answer 7

Even though light has no REST MASS (because it can never be at rest), it does have an effective mass which (it turns out) has all the properties one expects from MASS - in particular, it has weight in a gravitational field [photons can "fall''] and exerts a gravitational attraction of its own on other masses. The classic Gedankenexperiment on this topic is one in which the net mass of a closed box with mirrored sides increases if it is filled with light bouncing back and forth off the mirrors.

Answer 8

Light does not fall into a black hole it circles the event horizon for all time.

Answer 9

Light are balls of energy called photons. According to Einsteins e=mc^2 it has to have some mass. If it has mass then it has weight in a gravitational field.

Answer 10

The best answer to this is, "We do not know." That's because we do not understand gravity very well at all. Its effects can be measured and consequently predicted, but the mechanism is still a mystery.