speed... and possibly weight of light????

Question

ok..
basically.. i learnt that light has no mass, but has momentum..
which i can ish grasp..
i dont really understand why... but anyway..

right.. my teacher said, in theory, if you had scales you could actually measure the weight of light..
now... i think in weird ways, and was curious to what if it was a clear set of scales..
100% clear..
ok.. it would still have an impact... right??
it has a mass... so it will be effected..
the light will shine though it.. but be slightly slowed, and hence be defracted to the side...
now, its been slowed down, but when it leaves this clear solid, what speed will it be at??
presuming its a vacuum..
surely it wont be the speed of light in a vacuum, as it has lost momentum
although... how wouldnt it be?? all light travels at this speed in a vacuum, reguardless of what has happened to it.
Also... if it would be slower.. why cant we almost stop light?
then measure the weight of it??
just a few thoughts of mines..
thanks for the help..

Answer 1

There are two pools of thought on this.

Light has a constant speed of 3,000,000 m/s (About 186 kmph or something like that). But you are on the right lines of light hitting things having possible mass, its 3g if you care.

The other thought is that light has no mass because it does not have form. It is an elecromagnetic wave, like lazers, X-rays and radiation. We cannot see it, only the effects of it. On this basis, light has no Mass.

Incidentally, the speed of light is not fixed, it varies depending on numerous factors.

Its people like you that open the gates of wonder and push the frontiers of Science research to discover new stuff.

Answer 2

It's unclear if light has absolutely NO mass. Since light seems to contain or be made up of or assocaited with particles (Photons) it may have slight mass.

The mass of a black hole might be increased by the presence of photons from the light that can't escape.

Photons seems to generate a reaction of sorts, hence they might follow Newtonian physics to a degree.

Light bends with gravity, hence the particles and/or waves are affacted by gravity or space warps

Light from a laser can melt things

All of these factors indicates there might be more to light than we know.

Remember science or the lack of understanding of science tends to generate old wives tales.

Scientists hate to say "we don't know and can't explain" so they just mak opened ended statements and let the untrained mind fill in the blanks or make assumptions.

Light is also a relative commodity. To fully understand that, think of a dog whistle. YOU can't hear it but the dog can.

A blind person can't "see" light.

Light is a phenomenon that is sensed by us because our eyes react to it.

Our eyes don't react to infrared in the same concept, but if you take special photographic film and shoot a picture in a totally dark room of an iron turned on and heated up that film will show an image of iron.

MRI make images using tuned magnetic waves and sensors designed to sense them.

Gravity exerts an influence it is foolish to arbitrarily think a magnet doesn't.

A magnet has an effect on electrons and we are made up of electrons. A magnet must surely have an effect upon us.

The idea behind science is to question and solve.

Your teacher's statement make it sound like things have been solved and I'm not so sure that is absolutely correct.

His statements must either be backed up with warantees (you get some free education in the future if his statements turn out to change) or disclaimers.

The most probable statement is we THINK light may have no mass at this point in time.

Answer 3

I'LL TAKE THIS QUESTION

Light has no weight. Obviously. It has no substance, it can't have.

However. Light still has a presence. It zips through space, pretty quickly as it happens. It carries energy. Each light wave carries a tiny bit. not a lot, but a bit.

So imagine. Get a set of scales. Instead of a tray, it has a mirror.

The light shines on the scales.
The light and its energy is going to bounce off ?
Well of course, otherwise you'd not see the light from the mirror.


How does the light and energy change direction from DOWN onto the scales to UP offf the scales?

A force is needed to change the direction of ANYTHING. Masses? well obviously you need to push them. But energy....well yes. Think about it. Energy really exists. You need something to make it change direction.

But for every action, there is an equal and opposite reaction.

Bottom line. If light hits something, it'll push it. But not a lot.

This gross over-simplification came from....

Answer 4

Light has no rest mass.

It does, however, have mass.

Suppose you have two boxes lined with perfectly reflecting mirrors. When the boxes are empty, they balance on your scale. If you fill one of the boxes with photons and quickly slam down the lid, so that the photons are bouncing around inside the box, then that box will be heavier, by an amount given by Einstein's famous equation m = E/c^2, where E is the amount of energy of those photons.

Answer 5

I'm not sure that the light bounces off. I THINK it's absorbed by the atoms on the surface and sent out again, as the electrons that absorbed the energy pop back down to their lower levels of energy.

I don't think you can stop light. You can absorb it, with the energy being taken in by the electrons of whatever you're using. Thus, black things (that don't shoot light out again, but keep it), get hot.

The energy becomes heat, but there's no mass, no stuff-that-used-to-be-light.

I think.

Answer 6

Since light has no mass, then light can't have weight. Although lest we forget about gravity....

Since light can't escape the gravity of a black hole thats where you have stopped light. So in an experment if you could control gravity and slowly increased it, light eventually would slow down.

Answer 7

I'm not sure but Light is energy so can you weigh energy? Light can be stopped wit some extreme cold near absolute zero i think but i'm no expert. Related to this light thing is darkness, it's the absense of light right, it doesn't exist as a matter or energy but we can see it??

Answer 8

you lost me bit there mate but i don't think you can weigh light

Answer 9

Light has no rest mass and you can't weigh it.

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html