Does Light Travels In a Straight Line?

[Nicholas Kang]

If I shine a torchlight towards the moon, 90% of my light beam would be filtered by the atmosphere. Only 10% would reach the moon. Then, the light actually dispersed due to Heisenberg`s Uncertainty Principle. If so, does this mean light doesn`t travel in a straight line because there is a probability in which photons actually exist because it has a very high probability of existence? I mean photon may exist in anywhere within the probability region but not in a straight line motion then.

[Strange]

You are mixing up a couple of different things here.

 

When light is scattered in the air, it travels in straight lines between the atoms that it is scattered by.

 

Also, your torch (flashlight) shines light in a cone, so the light from that spreads out even though it travels in straight lines. It would be much, much less than 10% of your light that reaches the moon. In the lunar laser-ranging experiments, they shine a laser at reflectors on the surface of the moon (left by the Apollo mission). Out of gazllions of photons from the laser, they typically detect 5 reflected back to Earth.

 

Note that in quantum theory, we can't actually say anything about what photons do in the time before we detect them. (In QED, for example, you have to take every possible path into account.) But they always appear to have travelled in a straight line.

[Nicholas Kang]

I mean here is because we cannot say anything about photons do in time before we detect them, so there is a possibility in which photons may lie in a probability sphere, this mean photons, when traveling, may not in a straight line because the first photon that leads the beam would be in position A, say the influence sphere is 1mm. Position B is the next photon`s probably-exist-region. Then, photon C would have another probability to exist in a different area within the light beam. So, the photons` probability wave aren`t on the same straight alignment, instead they vary in a light beam. Although the light beam is straight from the outside but actually it seems to be not very straight if observed carefully. Moreover, quantum leap/tunneling allows photons to leak out of the light beam and further diverge the light beam, maybe allowing the photons to cross through a barrier like the air particles.

Edited July 23, 2014 by Nicholas Kang

[Strange]

If you watch the Feynman lectures on QED, he explains how you have to consider that the photon might have gone in every possible direction (and even at different speeds) with an appropriate probability. When you sum (integrate) all these paths you get to the result that ... the photon appears to travel in a straight line!

 

http://vega.org.uk/video/subseries/8

[Nicholas Kang]

Have any experiments been done for testing and verification purpose in this context? (Including measurement of light being a straight line.)

Edited July 23, 2014 by Nicholas Kang

[Mordred]

Have any experiments been done for testing and verification purpose in this context? (Including measurement of light being a straight line.)

 

 

lasers is one example, which you can only see via parts of the light hitting dust etc and being reflected to your eyes

Edited July 23, 2014 by Mordred

[Sensei]

Have any experiments been done for testing and verification purpose in this context? (Including measurement of light being a straight line.)

 

Search google for:

snell's law

diffraction

single and double slit experiment

you might also being interested about polarization filters.

 

These things are cheap to buy in shop with physics equipment. Do experiments with lasers, and mirrors.

Edited July 23, 2014 by Sensei

[MigL]

Since we define a 'straight' line with light, it must obviously travel that line.

More exactly, light follows the curvature ( if any ) of space-time. You would only be able to see a 'straighter' line if you were 'outside' space-time. i.e. That's as straight as your gonna get.

 

Edit:

Oops. Thought I was on 1st page, but actually 3 pages in. Old subject/OP.

Edited December 5, 2014 by MigL

[studiot]

For the purposes of this question you should look up

 

Fermat's Principle.

 

In simplest form this says

 

"Light takes the path of least time of travel."

[MigL]

Fermat's principle of least time is a generalization ( or is it the other way around ? ) of de Mauripitus' principle of least action, as it applies to massless particles ( such as light ) only.

[studiot]

Fermat's principle 1657

 

De Mauripitus 1698 – 27 July 1759 : Least Action

 

Born 40 years after Fermat's principle.

[MigL]

True.

But Fermat's principle is a subset of the principle of least action.

[Robittybob1]

For the purposes of this question you should look up

 

Fermat's Principle.

 

In simplest form this says

 

"Light takes the path of least time of travel."

That is wonderful.

[eswit12344]

Light does not travel in a strait line light can be bent around large masses etc. the Earth.

[Strange]

Light does not travel in a strait line light can be bent around large masses etc. the Earth.

 

It follows a "straight line" in curved space-time.

[eswit12344]

I didn't watch my words there sorry I'm just 14