what is the effect of gravity on light (on earth)?
is light considered to have weight ?
are photons considered matter ? what about when light is considered a wave ?
let’s say i shine a really strong beam of light (in the visible spectrum) over a very large distance on earth, what will the trajectory of the beam be ? essentially what i’m trying to ask is, if i shine a really strong torch with a concentrated beam from 10 metres above, say, sea level, will the beam be detected at the same height (i.e. 10 metres), say, 10 kms. away ? or will it be detected higher ? or lower ? and if the beam were particularly strong, theoretically, would the beam escape the earth or would it wrap along the surface ? if it does escape, what would be the trajectory of the escaping beam of light ?
what kind of harm can light waves from outside the visible spectrum do to the human body ? which rays are the most harmful to the human body ? case 1: looking straight into the beam. case 2: beam projected, say, through the torso.
what is the assumed trajectory of a beam of light within a black hole ? or what happens to light inside a black hole ? does it bounce around or is it absorbed completely and converted to some other energy or what ?
are there any fundamental flaws in my understanding of the behaviour and characteristics of light ? and should i know any other facts about light ?
i understand that these are a lot of questions… but they are all strongly related, so i thought i’d ask them in the same thread… also i do so wish they could each be answered.
if you’re not too keen on writing a detailed answer, i’d appreciate even a few short sentences or links to articles that could answer my specific queries.
if you know even part of the answers to part of the questions please do enlighten me.
::: creaking, rusted groan of old physics gears slowly rotating in my brain :::
I’ll take Door #4, please, Monty!
The curvature of the earth is such that your beam of light isn’t going to be found 10 m above the surface from 10 km away. Can you even SEE 10 km away, if the land is completely flat?
Then the atmosphere is going to affect the line of sight, through refraction.
According to my surveying textbook:
Now, that’s just SURVEYING. But when you are talking astronomical units, and light traveling across galaxies, IIRC, the light path will be affected by gravitational pull.
As to how much, we need to locate Mister Wizard.
~VOW
Light acts somewhat like a particle with a small mass (if it was stationary it would have no mass, but it has a mass related to its frequency due to going at the speed of light.) So it is affected by gravity, but not very much, and anyway is going so fast it isn’t affected for very long.
This is noticable mainly when its bent by the sun, or something. On earth the effect is negligable. There was some experiment where crystals that emitted/absorbed light of a very specific frequency showed that the frequency changed when light dropped towards the earth, gaining energy due to gravity.
Visible light lasers will burn you if they have enough energy. X-rays, gamma rays, and other high frequency radiation is more penetrating, so in can get inside you and give you cancer.
Maybe I don’t understand this. Anyone want to help?
On Earth, nothing noticeable will happen to your light beams. In principle, light (that is anything that has energy) will change its tragectory because of gravity. In practice, it requires a lot of mass to bend a light beam.
Weight… hmm… good question. Weight is defined by how much force you exert in a given gravitational field due to the gravitational field. So taking this at face value, yes, light has weight. However, I think you may be intending to ask whether light has mass. To which the answer is no.
Photons are not considered “matter” as they do not have rest mass. Light is a waveparticle just live everything else. (What you didn’t know that waves and particles were one and the same?)
The strength of the light or attenuation of the beam in principle has nothing to do with the trajectory. On Earth, the beam will go pretty much straight as an arrow (to an excellent degree of accuracy) since Earth isn’t quite massive enough to bend the light to what you can observe. However, theoretically someone should be able to observer the deviation, but it will be slight. The sun is massive enough to bend light, and was proven to do so in accordance with Einstein’s Theory of General Relativity during an eclipse in 1918.
Highly energetic light can cause radiative damage just like any other form of radiation. UV light causes skin cancer. The most highly energetic gamma rays at high intensity are theoretically the most damaging to the body (it doesn’t matter whether you look at the things as the eye is only sensitive to visible light, the effect is the same anywhere on your body).
A light beam bend enormously at a black hole to the point where its tragectory does not escape the “well”. We don’t know exactly what happens inside to the light as the laws of physics break down at the singularity. Just inside the event horizon, theoretically, light travels on just like it does anywhere else. AT the event horizon light travels forever never reaching anywhere as it remains in exact equilibrium. There are some black hole solutions to Einstein’s Field Equations that predict that light can pass on through to some “other place” when it enters a black hole. That’s pretty much speculation though.
For more information on Light and General Relativity, pick up Richard Gott’s book, Time Travel in Einstein’s Universe.
The gravitational field of the earth is too weak to have any noticeable effect on the trajectory of light. I think it’s not even detectable, but I’m not too sure about that.
Normal matter has a “rest mass”, i.e. mass when it isn’t moving. And when you accelerate normal matter, it gains more mass, i.e. “relativistic mass.” Photons have zero rest mass but non-zero relativistic mass.
Usually not, but that’s just a matter of definition (no pun intended).
The trajectory will be almost perfectly straight. Gravity will bend it a small amount, but atmospheric disturbances and temperature gradients will have a larger effect.
As already noted, high-energy photons (X-rays and gamma rays) penetrate your body and damages various molecules. If enough of your DNA molecules are damaged, cells will divide abrnormally and out of control - this is called cancer. If even more molecules are damaged, it will result in radiation burns. Ultraviolet light has the same effect but only on the skin, since it can’t penetrate deeper. Visible and infrared light are relatively harmless, but they still carry energy so it can heat up your skin. If the light bright enough you will get burned, as ants under a magnifying glass are. Microwave radiation also carries energy and it can penetrate into the body. We’ve all seen the effect of that in microwave ovens. The effect of lower frequency radio waves are more controvarsial - there is no immediate damage to the body, but there may be long-term effects on the nervous system.
6 and 7 I’ll defer to previous and following posts from others…
In Special Relativity, light travels in straight lines. In order to apply Special Relativity, we need to have an inertial reference frame. An inertial reference frame is not subject to gravity or acceleration. An inertial frame may be in a gravitational field provided it is in freefall. The acceleration and the gravity cancel each other out. So light would travel in a straight line as measured by a falling reference frame. A “Stationary” fame would be accelerating upward relative to the inertial frame. If you track a horizontal beam of light as your “stationary” frame accelerates upward, you will see that light “falls”. However, the acceleration due to gravity is only 9.80 m/sec[sup]2[/sup] while the speed of light is 299,792,458 m/sec. So the deviation from horizontal would be too slight to detect at 1 km.