# Light??

#### Alpha and 0mega

##### Junior Member
Light??

Can any brainys here tell me more about light,because i found that textbook doesn really tell me what lights really are and how it work??these are the questions that trouble me.

1)Does light loses its energy as it travels??

2)Is light a matter?can it be attracted by gravitational force?

3)As the textbook say,light is reflected.but in the book it show that light is only reflected to a certain angle.IF thats the case,why can we see everything??since not every light is reflected to our direction.?

#### Anon1986

##### New Member
Re: Light??

I dont know much on the subject but heres what I can tell you. Basically light is energy. Light is made up of particles, so it is matter. Supposedly light can not escape the gravitational force of a black hole. Again, I dont know much on the subject so someone correct me if I'm wrong here.

#### Harte

##### Senior Member
Re: Light??

<div class='quotetop'>QUOTE(\"Alpha and 0mega\")</div>
Can any brainys here tell me more about light,because i found that textbook doesn really tell me what lights really are and how it work??these are the questions that trouble me.

1)Does light loses its energy as it travels??

2)Is light a matter?can it be attracted by gravitational force?

3)As the textbook say,light is reflected.but in the book it show that light is only reflected to a certain angle.IF thats the case,why can we see everything??since not every light is reflected to our direction.?[/b]

A&O,
Really excellent questions. That's using the ol' noggin.

1)Does light loses its energy as it travels??
No. A light beam appears to lose energy because it widens as it travels so the light becomes more diffuse (weaker.) But the total energy in a beam of light stays the same until the beam hits something.

2)Is light a matter?can it be attracted by gravitational force?

Light, like everything else in existance, can be considered a wave or a particle. In either case light does have mass.

Gravity doesn't attract anything per se, gravity is defined by Einstein as a curved area in spacetime caused by a nearby mass. Think of how inertia pulls you to the left when you are in a car going around a curve to the right. Inertia tries to keep all motion in a straight line for objects with mass. The moon is always going around a curve (the orbit) but the moon does not feel the inertia trying to tug it back to a straight line. That's because, for the moon, the orbit is a straight line. The spacetime is curved so the straight line is curved.

When we have total solar eclipses, physicist go out and observe the positions of stars whose apparent positions are near the edge of the sun's disk. These stars are actually behind the sun but their light is bent by the curvature of spacetime near the sun and is thus curved around the sun and into our telescopes. The difference between the actual positions of these stars and the observed positions we see them at gives us a measure of this curvature. Einstein's general theory makes very precise predictions about this curvature and, so far, no measure made in this way has differed from Einstein's predictions in the least. So yes, light is affected by gravity in the same way everything else is, but "attracted" may not be the best word to use in describing this.

3)As the textbook say,light is reflected.but in the book it show that light is only reflected to a certain angle.IF thats the case,why can we see everything??since not every light is reflected to our direction.

Imagine looking at a flower in the sun. If all the light hitting the flower were reflected back to your eyes, it would be like looking at the sun in a mirror. Light hits the flower. Some of the light is absorbed, some is reflected. The reflected light is not all together, it is a "scattering" of waves/photons of different wavelengths/energy levels. Some reflected light goes into your eyes and you see the flower. Some reflected light goes the other way, over thewre where your friend is standing, and he sees the flower too.

Most books about this are trying to show what a mirror or a lens do to light. Mirrors reflect light very regularly, with very little scattering. But remember, even if you stand off to one side and can't see the image of your friend standing in front of the mirror, you can see the mirror itself.

Hope this helps.

Harte

#### thenumbersix

##### Member
Re: Light??

Hi,

1)Does light loses its energy as it travels??

light travels at the speed of light and general relativity tells us that at the speed of light time stops. Maybe then no time should pass for the light, so as far as it's concerned no energy need be disappated ?

2)Is light a matter?can it be attracted by gravitational force?

Is supposedly a matter and a wave, all at the same time. personally think we're just not looking at it in the right way, science is starting to agree. If it is matter then how comes when we slow it down to 30mph it doesn't increase in mass by a massive amount, I think it's pure enrgy forced into a mass state because it's travelling at the speed of light, probably can't decide which to be, either that or our observations of it speed it up slighly, forcing it to start to become mass ?

Yet black holes hold light in their event horizons, though they are weird creatures, space/time is pulled down to, supposedly, 'nothing'. It could be gravity doing it or maybe the massive curvature of space has a hand in it, we probably won't know until we fly up to one and start poking about.

3)As the textbook say,light is reflected.but in the book it show that light is only reflected to a certain angle.IF thats the case,why can we see everything??since not every light is reflected to our direction.?

Have read that light in partial reflection only reflects a specific percentage of the 'photons', something like 4 reflected to 96 passed through of 100, this causes the partial reflection. Not actually sure if that's relevant to the question or if it's just an indication to the properties of glass ?

#### StarLord

##### Senior Member
Re: Light??

Sometime soon Iggy will be in to discuss the Speed Of Dark....
..that was a fun discussion....

Re: Light??

heheh, -c ?

#### Alpha and 0mega

##### Junior Member
Re: Light??

OH i jus got this question,as u know newton law of motion,anything need a force inorder to move.so WHAT force is it that cause light to travel at such trememdous speed??

#### StarLord

##### Senior Member
Re: Light??

Why, the opposite force that keeps Dark stationary. ;-} Where's Iggy when you need him?

#### gl100

##### Member
Re: Light??

I think Newton's 3rd law refers to objects with mass. I'm not sure how it applies to electromagnetic waves. I'm sure there's an explanation but I only got a B- in college physics and that was a looong time ago.

#### Tenshi

##### New Member
Re: Light??

"Light, like everything else in existance, can be considered a wave or a particle. In either case light does have mass."

Light does not have mass. Light, obviously, travels at the speed of light, and anything that has mass cannot travel at the speed of light. So light has no mass.