Does light have mass?

Question

I know Stephen Hawking, and the general Scientific community have decided the answer to this is no, but then, why is it that light is affected by gravity? i.e. a black hole. These are famous for sucking light into them, and yet, surely gravity could not do that unless the atoms it was exerting force upon, had mass?

Answer 1

An excellent question. A simple (perhaps simplistic; I'm not all that familiar with quantum gravity...!) answer is that you *can* think of light as having mass, because it has *energy*. You know the famous equation E=mc^2? It says that mass and energy are the same type of thing: you can convert one into the other. Mass is just like "condensed" energy. (The equation also says that mass contains a staggeringly huge amount of energy, since c^2 has a magnitude of 9 x 10^16. Useful for nuclear reactors or atomic bombs).

So, since light has energy, it has mass via E = mc^2, and can be affected by a gravitational field.

When scientists say that "light has no mass", what they really mean is that light has no REST mass, i.e., if you could make light stop (which as far as we know, you can't), it wouldn't have mass. Did you know that fast-moving things have more mass than when they stand still? They have to be going at a significant fraction of the speed of light for you to see the difference, though.

Answer 2

No, light does not have mass.

This can be very accurately verified experimentally. But here's a clue that will show you that it cannot. The Earth is around 5 billion or more years old. The Sun has been shining on it all that time. But its mass has not gone up. If it had, it would have slowed down and moved to a more distant orbit.

Yes, light is affected by gravity. The mistake here is ever thinking that it would not be, and you probably made that assumption because it does not have mass and gravity is a force that acts on mass.

But this Newtonian view of gravity is wrong. The thought experiment here is to think of shining a light straight up. Do the photons lose energy as the climb under gravity away from the Earth. Well, if they do not, then this gives us a way to distinguish between reference frames and both Newtonian mechanics and the special theory of relativity must be wrong. But both of these are very accurately verified. So we must assume that yes, it does lose energy, and yes it is affected by gravity.

This was the assumption Einstein made to derive the general theory of relativity, which has also been verified.

Answer 3

"The short answer is 'no', but it is a qualified 'no' because there are odd ways of interpreting the question which could justify the answer 'yes'."

"The definition of the invariant mass of an object is m = sqrt{E2/c4 - p2/c2}. By this definition a beam of light, is massless like the photons it is composed of. However, if light is trapped in a box with perfect mirrors so the photons are continually reflected back and forth in the box, then the total momentum is zero in the box's frame of reference but the energy is not. Therefore the light adds a small contribution to the mass of the box. This could be measured - in principle at least - either by an increase in inertia when the box is slowly accelerated or by an increase in its gravitational pull. You might say that the light in the box has mass but it would be more correct to say that the light contributes to the total mass of the box of light. You should not use this to justify the statement that light has mass in general."

Answer 4

It might be better to ask if light, photon, or electromagnetic energy is able to become mass. The answer to this concept is that, yes, a photon is able to be formed into a mass (one definition of mass, being that which offers resistance to movement).

This is done when a high frequency photon approaches the core of an atom and the photon forms electron pairs. An electron is a physical mass, and offers resistance to movement. Both the electron and photon offer the potential of gravitational deflection because they are the same entity in different form.

Does it surprise you that steam and ice are both the same substance? Why should it seem strange that the photon and basic bits of matter should be one-and-in-the-same?

Answer 5

Should one bring to bear the Aristotelian conception of light, then the answer is indubitably NO. However, most in the physics community have come to accept the mistaken idea of light as the photon wave/particle. Temporal light, the photon particle, has ceased to be light. Non-temporal light is ineffable. Thus did Einstein declare the deep mystery of light. Einstein utilized the quantum effect of light to explain the photo-electric effect, (the first Solvay Conference) but was reticent to pass over the wave theory. Max Planck argued against the quantum of energy as directly physical, explaining it merely as a propensity of manifest matter to be affected by energy. The physicalist interpretation is limiting, but within such context it may appear reasonable to first, pose such a query, then to proceed to formulate a practical answer. You have not asked the right question to be afforded a proper revelation about the nature of light. You would best contemplate the ineffable aspect of light for the possible insight you seek.

Answer 6

No, light does not have mass. And no, gravity does not need the light to have mass to cause a change in it's direction. Not if you consider gravity as curved space-time like Einstein did instead of a force proportional to mass like Newton did.

Answer 7

Light doesn't not have mass. The reason light appears to be affected by gravity is, gravity affects the curve of the spce time continum itself. Light traveling across it muct follow the curve, but it is not affected by gravity directly.

Answer 8

Light is energy. It has no mass. But mass is another form of energy.

When objects move or has speed, its mass increases, But we are not adding any mass. The internal energy increases.

When a mass is moving its kinetic energy is given by the formula, increase in its mass times the speed of light.

Thus the rest mass of all objects alone are mass and increase in mass is understood as the one which gives the energy of motion ( kinetic energy).

When light is absorbed by matter, the energy is absorbed in quantas, namely hn. This energy is equivalent to a quantity of energy possesed by an increase of mass m times the square of the speed of light.(mcc).

Answer 9

A very debatable question! Light consists of photons. If they have mass, light have mass too. Currently most physicists believe photons are mass less{note the use of word most!}. So lights doesn't have mass too.

Answer 10

they say it does not. but the mass ould be converted to energy which light is form of. light is not affected by the gravity, but it is affected by the extremely high speed. and they r not sopposed to know everything