I heard that?

Question

I heard that light has weight. For example, for a black hole to "ingest" something, it has to have a weight. Light gets sucked into black holes on a continuous basis. Am I totally wrong, or is it a theory or a scientific fact?

Answer 1

It is not so much that black hole "ingest" things. A black hole is a black hole because things cannot escape it.

From Earth's surface, the escape speed is 11.2 km/s (very fast = 25,000 mph). So if you shoot something out at that speed in any direction (except into the ground, naturally) it will never fall back on Earth, in fact it won't even enter a closed orbit around Earth. It is gone. It has escaped.

The more mass an object has, the greater the escape speed. A black hole has an escape speed greater than the speed of light. Hence even light cannot escape.

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There are different ways in maths to look at the same problem. For example, e = mc^2 shows us that you can look at mass as some form of energy, and anything you can say about mass, you can say about energy (and vice-versa).

A photon has no rest-mass, therefore using the classical Newtonian equation: F = G * m1 * m2 / d^2 there should be no force because m2 = 0 (I'm using m2 as the mass of the photon).

However, a photon cannot exist at rest. A photon going at the speed of light has energy. For a photon of visible light, this is in the neighbourhood of 3 eV (electronvolts). Using e = mc^2, this can be converted to mass units. Very little mass (by comparison, the mass of an electron is 511,000 eV). You can use this equivalent mass of a photon in classical equations.

Another (equivalent) way to look at things is to imagine that space is curved by the presence of energy (including mass, a very concentrated form of energy). Then any object feels the influence of this curvature. Thus, a photon travelling in a "straight" line -- with no outside force acting on it -- will follow the curves of space. Thus, if there is a deep gravitational well caused by a very important mass, it may very well be that the photon (just at the right speed, in the right direction ) will turn downwards and never have enough speed to come back out. It does not get pulled into the black hole, it simply happens to follow the curvature of space.

Around a black hole, there is a distance called the event horizon. This is the distance at which the escape speed is exactly the speed of light. Anything that is closer to the black hole, we cannot see because even the light cannot reach us (it cannot escape the black hole).

If you were very close to the event horizon, strange things would happen. The gravitational field (meaning the difference in the force between two points OR the difference in the slope of the curvature) is very steep. For example, the gravity pulling on you feet would be so different from the gravity pulling on your head that your body would be pulled apart, even if you were on a stable orbit. In fact, molecules themselves don't survive and, in some extreme cases, even atoms get torn apart.

This tidal effect is called spaghettification (see link below) because all objects get pulled apart one way and squeeze together the other way.

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If you are well outside this event horizon, it's pretty well business as usual. If we could have a black hole with the same mass as our Sun, and if we were on a planet on a circular orbit at 150 million km from that black hole, then that planet would have an orbiting period of 365.25 days. It would not get sucked in to the black hole any more than we are getting sucked into our Sun.

There would be one long term difference: Our Sun is very slowly losing mass (putting out that much energy), so that our orbit will get larger over many millions of years. The black hole will gain mass over the same period so that the twin planet's orbit will slowly get smaller.

Answer 2

While it is true that light IS affected by gravity, it does NOT have mass, and therefore does not have weight. The force of Gravity in everyday objects is caused by General Relativity. This relativity theory states that objects with mass warp spacetime much as a bowling ball would put a dimple in stretched out piece of latex. Other objects with mass are prone to rolling down into this dimple.

However, light must never leave the plane of spacetime and must always travel in a "spacetime" linear path. In other words, the reason light curves around black holes and stars and the like is because the light beam follows the curve in spacetime caused by the massive object.

Be sure to note that light does not have mass and weight.

Answer 3

I have never heard that. I have been told that light gets pulled into a black hole because it cannot escapes the gravitational pull of a black hole.

Answer 4

E=MC2.
Energy and mass are equivalent and convertible.
Think of mass as super-concentrated energy.
Now, mass for sure gets sucked in and therefore so must energy because they are equivalent.

OR look at it this way;
A black hole is highly curved puncture in the fabric of space-time. It's strong curvature warps space which causes mass and energy and light to fall in.

Answer 5

I don't know if you could say that is has weight, but it has been proved that light is affected by gravity.

Answer 6

Light is caused by photons. I am sure photons have weight.