Does light only travel in straight lines

First.Aspect

I knew some physicists would come out of their caves eventually.

First.Aspect

Rick Chasey wrote:

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?

Ooh, I think I know the answer. There isn't a line between a and b, if there is a black hole in the way.

What coordinate system are you using, by the way?

rick_chasey

First Aspect wrote:

Rick Chasey wrote:

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?

Ooh, I think I know the answer. There isn't a line between a and b, if there is a black hole in the way.

What coordinate system are you using, by the way?

*shrugs* The only physics I did beyond A level was first year applied maths. Co-ordinates were given as a constant....

In my head I have a 3d version of this:


Where the mat is the 3d space.

DonDaddyD

Rick Chasey wrote:

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.

I'm reading this as it is possible to bend light. However it can only happen in exceptional circumstances.

Still means that light doesn't just travel in straight lines though....

Kieran_Burns

Not exceptional Don - gravity is universal, so the bending due to gravitational influence also happens everywhere

just more so in some places than others

First.Aspect

Kieran_Burns wrote:

Not exceptional Don - gravity is universal, so the bending due to gravitational influence also happens everywhere

just more so in some places than others

Like a cleavage, for example. My gaze is literally pulled towards one.

DonDaddyD

Kieran_Burns wrote:

Not exceptional Don - gravity is universal, so the bending due to gravitational influence also happens everywhere

just more so in some places than others

If it takes the gravitation force of a blackhole to bend light then the circumtances are exceptional.

If the gravitation force of a planet - say the size of Earth - could do it, then the circumstances are less so.

rick_chasey

DonDaddyD wrote:

Kieran_Burns wrote:

Not exceptional Don - gravity is universal, so the bending due to gravitational influence also happens everywhere

just more so in some places than others

If it takes the gravitation force of a blackhole to bend light then the circumtances are exceptional.

If the gravitation force of a planet - say the size of Earth - could do it, then the circumstances are less so.

Any gravitational force can bend light. Blackholes are good because it's just REALLY noticeable.

If it makes you feel better, since your penis has mass (you hope anyway), it too has the properties to bend light.

Try that on the missus next time.

First.Aspect

Rick Chasey wrote:

DonDaddyD wrote:

Kieran_Burns wrote:

Not exceptional Don - gravity is universal, so the bending due to gravitational influence also happens everywhere

just more so in some places than others

If it takes the gravitation force of a blackhole to bend light then the circumtances are exceptional.

If the gravitation force of a planet - say the size of Earth - could do it, then the circumstances are less so.

Any gravitational force can bend light. Blackholes are good because it's just REALLY noticeable.

If it makes you feel better, since your penis has mass (you hope anyway), it too has the properties to bend light.

Try that on the missus next time.

What *exactly* do you mean by the term "black hole"?

rick_chasey

First Aspect wrote:

Rick Chasey wrote:

Any gravitational force can bend light. Blackholes are good because it's just REALLY noticeable.

If it makes you feel better, since your penis has mass (you hope anyway), it too has the properties to bend light.

Try that on the missus next time.

What *exactly* do you mean by the term "black hole"?

walkingbootweather

... and what is the attractive force of Uranus?

greg66_tri_v2.0

First Aspect wrote:

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

I think many people would understand

First Aspect wrote:

Light travels in straight lines.

to mean

First Aspect wrote:

Light travels in straight lines.

rather than

First Aspect wrote:

Light travels in straight lines except for the times when it bends.

or

First Aspect wrote:

Light doesn't always travel in straight lines.

or

First Aspect wrote:

Light mostly travels in straight lines.

etcetera, etcetera...

Aside from that, your attempt to obfuscate your way out of the hole you have gotten yourself into is duly noted, and I commend your tenacity!

MonkeyMonster

surely light bends round DDD's legs as his power awesome fractures all aspects of the space time continuim anyway... at least until either a mouse comes along or someone re-indexes his gears.

First.Aspect

Greg66 wrote:

First Aspect wrote:

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

I think many people would understand

First Aspect wrote:

Light travels in straight lines.

to mean

First Aspect wrote:

Light travels in straight lines.

rather than

First Aspect wrote:

Light travels in straight lines except for the times when it bends.

or

First Aspect wrote:

Light doesn't always travel in straight lines.

or

First Aspect wrote:

Light mostly travels in straight lines.

etcetera, etcetera...

Aside from that, your attempt to obfuscate your way out of the hole you have gotten yourself into is duly noted, and I commend your tenacity!

Did light travel in a sraight line between the cyclist and the car, yes or no?

Now, Mr. Gregtastic, back to the whole refraction thing - Do you acually KNOW whether or not, on the subatomic scale light refraction entails any actual bending, or are you just hoping after all of this that it doesn't? (I know the answer to this one).

And can you PLEASE explain why you started banging on about refraction to explain light bending due to gravity?

Really the hypocrisy of accusing me of obfuscation beggars belief. I wish lawyers would stick to what they are good at, or at the very least find someting that they are good at.

Eyon

Rick Chasey wrote:

First Aspect wrote:

Rick Chasey wrote:

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?

Ooh, I think I know the answer. There isn't a line between a and b, if there is a black hole in the way.

What coordinate system are you using, by the way?

*shrugs* The only physics I did beyond A level was first year applied maths. Co-ordinates were given as a constant....

In my head I have a 3d version of this:


Where the mat is the 3d space.

^^ This.

Space time isn't flat but for us it appears so, thus light always appears to go in strait lines, however in reality if the theory of relativity is correct (and we should assume so because nobody has proved otherwise) then light is very bendy.

Nearly did a degree in astrophysics, maybe it was good I did not otherwise I would be even more boring than I am currently

greg66_tri_v2.0

First Aspect wrote:

And can you PLEASE explain why you started banging on about refraction to explain light bending due to gravity?

I didn't. I chose a different example to illustrate light bending:

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.

I don't know where you've got the idea that I was suggesting that gravtitational lenses operate by refraction.

Reading is an undervalued skill. But an overvalued place.

DonDaddyD

MonkeyMonster wrote:

surely light bends round DDD's legs as his power awesome fractures all aspects of the space time continuim anyway...

My thighs would bend light, if light could actually catch up!

ballspondroad

It's space-time that is bendy not light.

Nelson Longflap

Asprilla wrote:

First Aspect wrote:

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

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.

Same with me. Degree level physics got a bit tricky when doing general relativity and in depth quantum mechanics. Drifted into IT, then played around with financial derivatives for a bit, and am now in the film industry!

Anyway, haven't read the entire thread too closely, but ignoring relativistic effects, light takes all paths in a medium (and gets slowed down on encountering it), some paths even going backwards, sideways and behaving in non-logical ways. What we end up seeing as a beam of light is effectively the summation of all the little wavelets (photons) with near identical phase-angles. The behaviour of things at a very, very small scale is entirely bonkers and is almost impossible to conceptualise. It's almost easier to think of things behaving as neither a particle nor a wave, but as a summation of probabilities. As usual Richard Feynmann explains it best in what he called quantum electrodynamics (QED). He got a Nobel prize for it

http://en.wikipedia.org/wiki/QED:_The_S ... and_Matter

The book is worth a read.

First.Aspect

Greg66 wrote:

I didn't. I chose a different example to illustrate light bending:

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.

I don't know where you've got the idea that I was suggesting that gravtitational lenses operate by refraction.

Reading is an undervalued skill. But an overvalued place.

I guess I'm still confused.

I think I follow that light refracts (Monopoly). Great, so how does that help me towards understanding relativity? (Global Financial Crisis).

What if someone doesn't understand refraction? Do you "explain" it by pointing out that light is made up of all different colours? Or would that not be relevant in the least?

greg66_tri_v2.0

First Aspect wrote:

I guess I'm still confused.

You see? I *knew* we'd agree in the end!

First.Aspect

Greg66 wrote:

First Aspect wrote:

I guess I'm still confused.

You see? I *knew* we'd agree in the end!

Step (1) Steal underpants
Step (3) Profit

What's step (2), Greg? Pleeeeeaaaaase tell me.

jimmypippa

First.Aspect

jimmypippa wrote:

snailracer

^^^
That traces light beams in step-index fibre. In more modern graded-index and single-mode fibre, the light actually flows in smooth curves.

jimmypippa

snailracer wrote:

^^^
That traces light beams in step-index fibre. In more modern graded-index and single-mode fibre, the light actually flows in smooth curves.

Indeed.

Or if light is traveling at an angle* to a smoothly changing refractive index, it will curve.

*not 0°,90° or 180°

tailwindhome

First Aspect wrote:

Greg66 wrote:

First Aspect wrote:

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

I think many people would understand

First Aspect wrote:

Light travels in straight lines.

to mean

First Aspect wrote:

Light travels in straight lines.

rather than

First Aspect wrote:

Light travels in straight lines except for the times when it bends.

or

First Aspect wrote:

Light doesn't always travel in straight lines.

or

First Aspect wrote:

Light mostly travels in straight lines.

etcetera, etcetera...

Aside from that, your attempt to obfuscate your way out of the hole you have gotten yourself into is duly noted, and I commend your tenacity!

Did light travel in a sraight line between the cyclist and the car, yes or no?

Now, Mr. Gregtastic, back to the whole refraction thing - Do you acually KNOW whether or not, on the subatomic scale light refraction entails any actual bending, or are you just hoping after all of this that it doesn't? (I know the answer to this one).

And can you PLEASE explain why you started banging on about refraction to explain light bending due to gravity?

Really the hypocrisy of accusing me of obfuscation beggars belief. I wish lawyers would stick to what they are good at, or at the very least find someting that they are good at.

Ignore Greg, he's a know-all control freak who must always be right.

He has a Brian Clough complex.

Lazarus

Rick Chasey wrote:

Have got a clue what your all talking about but I do know that's a nasty dent you have in your top tube there Rick.

EKE_38BPM

Lazarus wrote:

Rick Chasey wrote:

Have got a clue what your all talking about but I do know that's a nasty dent you have in your top tube there Rick.

I assume you mean "Haven't got a clue..." rather than "Have got a clue..."
[/pedant]

Specialized Needs

DonDaddyD wrote:

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

Nelson Longflap wrote:

Same with me. Degree level physics got a bit tricky when doing general relativity and in depth quantum mechanics. Drifted into IT, then played around with financial derivatives for a bit, and am now in the film industry!

DDD - here's your chance ...