Does light only travel in straight lines

DonDaddyD

This'll keep me active until my upcoming "what porn star" friday thread...

First Aspect wrote:

Mr Sworld wrote:

First Aspect wrote:

Light travels in straight lines.

If you can prove that then there will be an shitload of Quantum Physicists interested in talking to you about wave-partical duality. Also quite a few Astrophysicists might be phoning you up from Honolulu.

May I be the first to congratulate you on your imminent Nobel Prize BTWl.

Light does travel in straight lines, its space which is bent. Don't you know nuffink?

So does it, light I mean, does it travel and can it only travel in straight lines?

Also is space gay? I thought it was a infinite expanse, while some would like to claim that it is spherical....

And finally what is the major significance or the intersting point about light being able to act as both a wave and a particle?

[It may be a long week]

rick_chasey

No.

http://en.wikipedia.org/wiki/Gravitational_lens

dhope

Space is almost certainly bi. Given its infinite size the chance that at least some of it swings one way and some the other tends to 1.

First.Aspect

Oh, its in wikipedia, so it must be true.

Here's the question - how to you define "straight"? If spacetime itself is distorted, and light propogates in a certain predictable way in relation to space time, does it travel in a straight line? (item 3 in the wikipedia entry).

Honestly, I haven't a clue.

greg66_tri_v2.0

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

asprilla

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

It gets bent when it passes between any two mediums of different density provided the exit isn't exactly perpendicular to the interface of the two mediums.

greg66_tri_v2.0

Asprilla wrote:

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

It gets bent when it passes between any two mediums of different density

This is true.

As we had started with gravitational lenses in space, I thought I'd start with one or two easy examples that we all might have come across though...

walkingbootweather

I've found that pretty much all heavenly bodies are attracted to me (and me to them). If space isn't attracted to me then it MUST be gay (No Homo).

QED

rick_chasey

Greg66 wrote:

Asprilla wrote:

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

It gets bent when it passes between any two mediums of different density

This is true.

As we had started with gravitational lenses in space, I thought I'd start with one or two easy examples that we all might have come across though...

I went for the most curved example I could think of.



This kinda stuff always feels like there's a couple of kinks, rather than curved bends...

First.Aspect

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

I find the way complex financial instruments work conceptually difficult, so lets have a look at the rules of Monopoly instead. It doesn't help, exactly, but you do get a warm glow of at least having understood something.

Kieran_Burns

Light does not travel in a straight line, if it did Black Holes would not exist.

DonDaddyD

Rick Chasey wrote:

Greg66 wrote:

Asprilla wrote:

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

It gets bent when it passes between any two mediums of different density

This is true.

As we had started with gravitational lenses in space, I thought I'd start with one or two easy examples that we all might have come across though...

I went for the most curved example I could think of.



This kinda stuff always feels like there's a couple of kinks, rather than curved bends...

I'm seeing three straight lines. Yes the beam of light may have originated from a single point of origin but it's still three straight lines the middle being out of synch with the other two.

Also light as waves and particles whats the significance?

First.Aspect

Kieran_Burns wrote:

Light does not travel in a straight line, if it did Black Holes would not exist.

Forehead = palm.

asprilla

DonDaddyD wrote:

Rick Chasey wrote:

Greg66 wrote:

Asprilla wrote:

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

It gets bent when it passes between any two mediums of different density

This is true.

As we had started with gravitational lenses in space, I thought I'd start with one or two easy examples that we all might have come across though...

I went for the most curved example I could think of.



This kinda stuff always feels like there's a couple of kinks, rather than curved bends...

I'm seeing three straight lines. Yes the beam of light may have originated from a single point of origin but it's still three straight lines the middle being out of synch with the other two.

Also light as waves and particles whats the significance?

Yeah, but the light curves between the lines, hence they point in different directions.

Light curving at a boundary like that is a direct result of it's wavelike properties as opposed to it's particle like properties.

greg66_tri_v2.0

First Aspect wrote:

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

I find the way complex financial instruments work conceptually difficult, so lets have a look at the rules of Monopoly instead. It doesn't help, exactly, but you do get a warm glow of at least having understood something.

Oooh - counter the patronising with sarcasm. Good work.

Except that there are no complex financial instruments in Monopoly. Much less in the rules of Monopoly. Whereas if you wear glasses, or have looked at someone through a beer glass, you'd have known that your first statement was, well, as they say in the peer reviewed physics journals, wrong.

Have one of these:



G'bye now!

First.Aspect

Greg66 wrote:

Asprilla wrote:

Greg66 wrote:

The question of whether light travels in a straight line when space itself is bent is rather difficult, conceptually.

A bit easier to grasp is that light gets bent when it passes through a regular glass optical lens.

Also gets bent as it passes from air to water/water to air.

It gets bent when it passes between any two mediums of different density

This is true.

As we had started with gravitational lenses in space, I thought I'd start with one or two easy examples that we all might have come across though...

Refraction is an entirely different phenomenon. And explaining what it is shouldn't be confused with explaining why. Its like explaining why an apple falls from a tree, and so that's how CD's work.

I'd love you guys to have a stab at diffraction now.

Kieran_Burns

First Aspect wrote:

Kieran_Burns wrote:

Light does not travel in a straight line, if it did Black Holes would not exist.

Forehead = palm.

Well, that's just rude

asprilla

First Aspect wrote:

I'd love you guys to have a stab at diffraction now.

What do you want to know?

I must admit it's been 15 years since I've used my physics degree and I've tried to forget most of it, but I'll see what I can drag up from the recesses of my mind.....

rolf_f

Kieran_Burns wrote:

First Aspect wrote:

Kieran_Burns wrote:

Light does not travel in a straight line, if it did Black Holes would not exist.

Forehead = palm.

Well, that's just rude

And technically wrong. It would be like answering DDD by saying light=prism!

But obviously you are an idiot

veronese68

Of course it doesn't. I come across drivers that can see round corners every day. Or, at least they think they can, the twunts.

First.Aspect

Greg66 wrote:

Oooh - counter the patronising with sarcasm. Good work.

Except that there are no complex financial instruments in Monopoly. Much less in the rules of Monopoly.

My point exactly, old chap.

So explain why my first statement was wrong. Start off by drawing a very very long straight line. What is it straight in relation to? Space, perhaps? Well, in that case its bent, or is it? Now shine a laser along your straight line. The beam perfectly follows the straight line. So is it straight, or bent? Does it matter whether or not there's a large mass in your imaginary space? Does the light bend away from your "straight" line, or does the line itself simply bend more.

Refraction of electromagnetic radiation by other electromagnetic phenomena (such as matter) isn't that hard to understand. Well, it is, once you start thinking about whether its a wave or a particle, but then you are limiting yourself to thinking of it as a wave or a particle, rather than a phenomenon having properties more commonly ascribed to one or the other in our macroscopic perspective. Anyway, I guess bending light gets easier to believe if you think of light as a particle, with a mass, so obviously its affected by gravity. Which is a wave. Or simply a property of matter.... which is made up of particles, which are waves.

Are you following this, or are you still too busy taking things too seriously?

Jesus, we are over run with lawyers and IT people on this forum, where are all the damn physicists?

asprilla

First Aspect wrote:

Jesus, we are over run with lawyers and IT people on this forum, where are all the damn physicists?

Basic statistics; there are more lawyers and IT folk in the UK than there are physicists. 15 years go when I did my degree it was the final year that they offered Geophysics and Cosmology classes were getting to the point of unsustainable as well.

I enjoyed physics at A level, but not at Uni. After graduation I jacked it all in and went into IT. I suspect I wasn't alone.

greg66_tri_v2.0

First Aspect wrote:

Greg66 wrote:

Oooh - counter the patronising with sarcasm. Good work.

Except that there are no complex financial instruments in Monopoly. Much less in the rules of Monopoly.

My point exactly, old chap.

So explain why my first statement was wrong. Start off by drawing a very very long straight line. What is it straight in relation to? Space, perhaps? Well, in that case its bent, or is it? Now shine a laser along your straight line. The beam perfectly follows the straight line. So is it straight, or bent? Does it matter whether or not there's a large mass in your imaginary space? Does the light bend away from your "straight" line, or does the line itself simply bend more.

Refraction of electromagnetic radiation by other electromagnetic phenomena (such as matter) isn't that hard to understand. Well, it is, once you start thinking about whether its a wave or a particle, but then you are limiting yourself to thinking of it as a wave or a particle, rather than a phenomenon having properties more commonly ascribed to one or the other in our macroscopic perspective. Anyway, I guess bending light gets easier to believe if you think of light as a particle, with a mass, so obviously its affected by gravity. Which is a wave. Or simply a property of matter.... which is made up of particles, which are waves.

Are you following this, or are you still too busy taking things too seriously?

Jesus, we are over run with lawyers and IT people on this forum, where are all the damn physicists?

This is fascinating. But all rather off the point (and less charitably, an attempt to run away behind a smokescreen of irrelevance).

Your first statement was

First Aspect wrote:

Light travels in straight lines.

It doesn't. I don't have to explain why it doesn't in order to show this statement is wrong. I can show it is wrong with some simply everyday examples.

Changing your position to one that is based on the question "why doesn't light travel in straight lines" doesn't make your statement any less wrong.

Anyway, back to your example. I've drawn my line. I've tracked it with a laser. Then I put a glass lens in the way. Guess what happened!

Cutting to the chase, do you contend that light doesn't bend with it passes between two media with different densities? If so, I assume you can draw a triangle with one straight line.

ballspondroad

Light always travels in straight lines if you define a straight line as the shortest distance between two points. In some cases this means that the 'straight' line is bendy.

rick_chasey

ballspondroad wrote:

Light always travels in straight lines if you define a straight line as the shortest distance between two points. In some cases this means that the 'straight' line is bendy.

Even in the case of the gravity lens?...?

ballspondroad

Even then - the path taken by light in the region of the gravitational lens is the shortest possible path and is therefore a straight line according to the definition.

rick_chasey

ballspondroad wrote:

Even then - the path taken by light in the region of the gravitational lens is the shortest possible path and is therefore a straight line according to the definition.

Really? Even if we take space to be 3d?

So from co-ordinate a to co-ordinate b? If there's a black hole inbetween then?

First.Aspect

Well, Greg, Greggy, the Gregster, now you are adding things into the original statement which aren't there.

I said, "light travels in straight lines." You say that it doesn't because it can be made to bend. Which means, I assume, that you think it does travel in straight lines unless you put something in its way, like an interface between media having different refractive indices. I think what you are saying is that in the absence of such an interface, light travels in straight lines, which means you agree with my original statement.

Or did you think I was implying that light always travels in straight lines?

Depending on one's concept of scale, It might, I really don't know. I don't even know whether it "bends" when it passes (at anything other than 90 degrees) through the interface between air and water. It most probably depends on your concept of scale. The thing with "everyday observations" as you put it, is that they are limited to a scale wherein even a line parallel to the ground (which is clearly a part of the circumference of a circle) appears to be straight and where Newton was, and still is, spot on.

So "everyday observations" are not a whole lot of use in explaining either quantum or relativistic phenomena, are they?

You made the point about refraction, in the context of explaining that light could bend around stars. Where is the refraction taking place, when light "bends" around stars? Its an entriely unrealted observation which has some superficial similarities to refraction, i.e. something isn't straight. A bit like the observation that Monopoly is something to do with money, and so are complex financial derivatives. So, I guess if I can get to grips with Monopoly, I will be on my way to understanding the financial crisis, right?

Yes, it was sarcastic.
I confess.
Hit me with the comfy pillows Cardinal Biggles.

rjsterry

Rick Chasey wrote:

ballspondroad wrote:

Even then - the path taken by light in the region of the gravitational lens is the shortest possible path and is therefore a straight line according to the definition.

Really? Even if we take space to be 3d?

So from co-ordinate a to co-ordinate b? If there's a black hole inbetween then?

Shortest possible - i.e. it's not shorter to go 'straight through'.

Common sense is no longer your friend.

First.Aspect

rick_chasey

rjsterry wrote:

Rick Chasey wrote:

ballspondroad wrote:

Even then - the path taken by light in the region of the gravitational lens is the shortest possible path and is therefore a straight line according to the definition.

Really? Even if we take space to be 3d?

So from co-ordinate a to co-ordinate b? If there's a black hole inbetween then?

Shortest possible - i.e. it's not shorter to go 'straight through'.

Common sense is no longer your friend.

Yeah but it's not that simple. Take a look at your shadow. There comes a point where the light won't get past something. The reason we see light bend round a black hole is because it has an immense gravitational field which illustrates the 'gravity lens' perfectly.

If a similarly sized black object which had a tiny gravitational field (so probably a very small mass) went past a galaxy like in the above picture, we wouldn't see the bend effect.