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Name:  Sonya L.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 2000-2001

okay, I've been telling my students that light doesn't have mass. That it is the only thing that doesn't because this is what I learned. However, a friend told me that they are deflecting light in a wind tunnel at NASA could this be correct? Does electromagnetic radiation have mass?


It is true that light does not have mass. However, it does have energy and momentum. This is at the level of quantum mechanics. It is possible for light to interact with charged particles, such as electrons. Momentum can be transferred to the light and deflect it slightly.

Dr. Ken Mellendorf
Illinois Central College

Nope, you are right, light does not have mass. As far as I understand, general relativity will not hold up if it does. I am not familiar with the experiments you mentioned, so I do not know their implications. But if they showed that light has mass, I am sure it would have caused enough of a stir that I would have heard of it by now.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois

Light does not have mass. It is not unreasonable that light would be deflected in a wind tunnel by variations in air pressure, which would result in variations in refractive index.

Tim Mooney

Hi, Sonya !!

I also learned that an electromagnetic wave (=EMW) does not carry mass, but carries energy. But some other aspects should also be considerated, like momentum, for instance. An EMW exert pressure, what means, it has inertia.

Well, have you heard that Einstein has been in Brazil some decades ago ? He was there because by that time a star should be eclipsed by a very massive body. In this case, the light should - according to his theory - make a curve and deviate from its original direction, so that you still will see the star although it was not to be seen. And that is what happened by that time. The light was deviated because of the gravity of the very massive body in space.

So, this seems to prove that light has mass and was deflected by the gravitational field of the body.The general conception is - however - that EMW have no mass. The famous Einsteins equation E=m.c^2 shows us that mass is a very concentrated form of energy, as you know. And EMW is energy.

Best Regards

Alcir Grohmann
Beschaffung SAM

Light is refracted in wind tunnels due to differences in the density of the air as it flows around objects. As the density changes, so does the index of refraction.

Greg Bradburn

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