[swansont]

Constant SOL is part of Maxwell's equations.

[Mystery111]

swansont, on 2 November 2011 - 10:22 AM, said:

How does a photon decay? Decay is a spontaneous process, so if something is happening, it must be through interaction, and I addressed that: "Light that doesn't interact keeps on going. It does not decay."

Ah, then I've been a right tit and not read you correctly

[morgsboi]

Light is slowed down by anything, glass, diamond and even air. It probably just can't be sped up.

[Mellinia]

Quote

Light is slowed down by anything, glass, diamond and even air. It probably just can't be sped up.

I thought the "speed of light being slowed down"-thing is because of the delay in between the absorption of light photons and their release by the particles, and the the speed of light in between transfer is still c, only the total speed is a little smaller....

This post has been edited by Mellinia: 5 November 2011 - 08:22 AM

[swansont]

Mellinia, on 5 November 2011 - 08:21 AM, said:

I thought the "speed of light being slowed down"-thing is because of the delay in between the absorption of light photons and their release by the particles, and the the speed of light in between transfer is still c, only the total speed is a little smaller....

Yes. The statements are not actually contradictory. Photons travel at c, but the propagation speed of the light (distance/time) is reduced.

IOW "speed of light" ≠ "speed of photons"

There is ambiguity in the imprecise way we phrase things.

[Mellinia]

So when people speak of light, they don't mean speed of photons, but the speed of propagation of light? This clears up a lot! Thanks, swansont.

[swansont]

Mellinia, on 5 November 2011 - 11:21 AM, said:

So when people speak of light, they don't mean speed of photons, but the speed of propagation of light? This clears up a lot! Thanks, swansont.

The can be talking about that or they could be referring to c, the speed of light in a vacuum, which is the speed of photons. That's the source of a decent amount of confusion.

[superball]

Perhaps light can change speed under certain conditions.

http://news.harvard....-stoplight.html

white rabbit.
cheers.

[swansont]

superball, on 18 November 2011 - 08:59 AM, said:

Perhaps light can change speed under certain conditions.

http://news.harvard....-stoplight.html

white rabbit.
cheers.

That's not in a vacuum — the light is interacting with atoms. This has been discussed several times in other threads

[The time Traveller]

When light passes a large body in the universe the gravity of the said mass causes the light to bend and curve around the mass.

so in theory the light adjacent to the light that has just curved around the mass will be travelling faster as the curved light has travelled a greater distance.

so there for one or the other would have had to of travelled at a different speed,

its not possible for some thing travelling at a constant to cover a greater distance eg the straight line is say 500.000miles and the curved line is 510.1740 miles.

how can something with the same speed and velocity cover two different distances at the same time and speed QED

[Mellinia]

The time Traveller, on 8 December 2011 - 11:36 PM, said:

When light passes a large body in the universe the gravity of the said mass causes the light to bend and curve around the mass.

so in theory the light adjacent to the light that has just curved around the mass will be travelling faster as the curved light has travelled a greater distance.

so there for one or the other would have had to of travelled at a different speed,

its not possible for some thing travelling at a constant to cover a greater distance eg the straight line is say 500.000miles and the curved line is 510.1740 miles.

how can something with the same speed and velocity cover two different distances at the same time and speed QED

But the reason why light is curved is because spacetime is curved so that light speed is constant....to light, there is no curve, to us, there is...

[Sorcerer]

baric, on 1 November 2011 - 01:46 PM, said:

All measurements of the speed of light have been constant. The notion of a speed of light "decay" is an old creationist attempt to explain away the age of the universe as given by redshift measurements of distant galaxies

Well who cares what they think, but u shouldn't just dismiss an idea because some idiot was using it for the wrong reasons.

I was thinking about this and wouldn't a change in the speed of light allow alternate, and perhaps more simple explanations for inflation and dark energy?

This post has been edited by Sorcerer: 21 December 2011 - 02:47 AM

[swansont]

Sorcerer, on 21 December 2011 - 02:39 AM, said:

I was thinking about this and wouldn't a change in the speed of light allow alternate, and perhaps more simple explanations for inflation and dark energy?

But there are other implications. You can't tug on one area of physics without changing it elsewhere. You "solve" one problem and cause dozens of others.

[Sorcerer]

Shows how sensitive occam's razor is when it comes to complex things.

Swansont I don't disagree, I wasn't actually afirming anything.

This post has been edited by Sorcerer: 21 December 2011 - 11:21 AM

[JustinW]

Quote

All measurements of the speed of light have been constant. The notion of a speed of light "decay" is an old creationist attempt to explain away the age of the universe as given by redshift measurements of distant galaxies

Yes, I stand corrected. What I was trying to recall was about photons reacting with other material, not about speed in a vacuum. I don't know if creationalists had anything to do with it though, and I don't recall any mention of red shifts either.

[michel123456]

See also The varying speed of light cosmology

[JustinW]

Thanks for the link. It made me remember a few questions I've had in the past. I find it weird, to say the least, that light slows down through a medium but once out of the medium continues at it's origional speed. Does anyone know why? I've found it a little hard to grasp and asked myself how it could be propelled back to the origional speed without some outside influence affecting its increase in velocity and frequency.

Also, if a photon has no mass, why would a medium have any affect on it at all? I understand that a medium might have an affect on its frequency, but doesn't a frequency constitute having mass in the first place? Doesn't a frequency come from the oscillations of mass-having objects?

This post has been edited by JustinW: 21 December 2011 - 05:26 PM

[imatfaal]

JustinW, on 21 December 2011 - 05:23 PM, said:

Thanks for the link. It made me remember a few questions I've had in the past. I find it weird, to say the least, that light slows down through a medium but once out of the medium continues at it's origional speed. Does anyone know why? I've found it a little hard to grasp and asked myself how it could be propelled back to the origional speed without some outside influence affecting its increase in velocity and frequency.

Also, if a photon has no mass, why would a medium have any affect on it at all? I understand that a medium might have an affect on its frequency, but doesn't a frequency constitute having mass in the first place? Doesn't a frequency come from the oscillations of mass-having objects?

The simple heuristic is that the photon travels between interactions at the speed of light but in any medium it will also interact with the particles of that material. and when interacting with the atoms of the material the photon is absorbed and re-emitted which takes time. ie when travelling the speed is c - but the progress of the beam is slowed by the time of the interactions

[JustinW]

Quote

The simple heuristic is that the photon travels between interactions at the speed of light but in any medium it will also interact with the particles of that material. and when interacting with the atoms of the material the photon is absorbed and re-emitted which takes time. ie when travelling the speed is c - but the progress of the beam is slowed by the time of the interactions

Yes that makes sense. But you would think, or this is just my simpllistic way of thinking, that to have any interaction at all, it would have to hold mass to some degree. And how does anyone explain light frequency if there is no mass oscillation to create one?

[Sorcerer]

JustinW, on 21 December 2011 - 06:16 PM, said:

Yes that makes sense. But you would think, or this is just my simpllistic way of thinking, that to have any interaction at all, it would have to hold mass to some degree. And how does anyone explain light frequency if there is no mass oscillation to create one?

Matter absorbs the light at certain wave lengths, it doesn't need mass it has/is energy (E=mc^2). The light is then emited again. Electrons can move between shells using photons, when they lose that photon they jump down a shell and floresce. Hence glow in the dark materials/minerals.