Another dumb fisics question.

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Another dumb fisics question.

Post by Rum » Thu Jan 11, 2018 12:57 pm

The speed of light, right?

Is light limited to the speed of light because that's how fast light travels - or - does it travel at the speed of light because the laws of the universe won't allow it to go faster.

It isn't as basic a quetion as it might seem at first sight.

Or maybe it is... :ask:

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Re: Another dumb fisics question.

Post by Tero » Thu Jan 11, 2018 1:46 pm

(It all goes to Planck's constant.)

Well, it looks like we can measure distance. Not sure about this time, but since there is regular motion of planets around a sun, I suppose there is time. So there is units of distance/units of time.

Also, light comes from particles, which have fixed size. Light has frequency and wavelength. This is because it is a bit of energy from electrons jumping from orbit to orbit. To have frequency and wavelength you have to have speed.

Here is where I had to google: see the link
To find the photon energy in electronvolts, using the wavelength in micrometres, the equation is approximately

{\displaystyle E(eV)={\frac {1.2398}{\mathrm {\lambda } ({\mu }m)}}} E(eV)={\frac {1.2398}{{\mathrm {\lambda }}({\mu }m)}}

Therefore, the photon energy at 1 μm wavelength, the wavelength of near infrared radiation, is approximately 1.2398 eV.

Since {\displaystyle {\frac {c}{\lambda }}=f} {\frac {c}{\lambda }}=f, where f is frequency, the photon energy equation can be simplified to

{\displaystyle E=hf} E=hf
https://en.wikipedia.org/wiki/Photon_energy
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Re: Another dumb fisics question.

Post by Feck » Thu Jan 11, 2018 4:31 pm

I'm still trying to find out why the light "slows down ? " inside liquids, glass etc ....
It isn't as basic a quetion as it might seem at first sight.
I've still never found an explanation that isn't full of holes .
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Re: Another dumb fisics question.

Post by laklak » Thu Jan 11, 2018 5:34 pm

Because Jesus wants it to slow down, of course.
Yeah well that's just, like, your opinion, man.

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Re: Another dumb fisics question.

Post by Tero » Thu Jan 11, 2018 5:35 pm

It's because it hit matter. it is going into its particle mode and has to visit all the family and friends and friendly orbitals in the water. Then it goes back to wave when it comes out.
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Re: Another dumb fisics question.

Post by Feck » Fri Jan 12, 2018 12:58 am

The particles not scattered, just all slowed down equally !?
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Re: Another dumb fisics question.

Post by pErvinalia » Fri Jan 12, 2018 1:35 am

This is a good question, Rum. I've got no idea. I suspect it's both of your explanations, but no idea why that would be the case.
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Re: Another dumb fisics question.

Post by JimC » Fri Jan 12, 2018 4:09 am

I have a memory (which may be faulty) that the actual speed emerges from Maxwell's equations, the highpoint of classical, pre-relativity Physics. Relativity itself uses this speed, but in the context of it being a universal maximum speed.

As to the slowing of light through glass etc. it certainly is based on a series of interactions between individual photons and the electron clouds of the constituent atoms.
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Re: Another dumb fisics question.

Post by mistermack » Mon Jan 15, 2018 2:09 am

There are two fundamental aspects to the speed of light.
Firstly it's a property of space itself. Imagine empty space as a row of dominoes standing up ready to be toppled.
Something pushes the first domino, and then the toppling event travels along the row, each domino passing on the disturbance to the next. The moving disturbance is like the light photon.
The dominoes can't fall any faster, no matter how fast or hard the first one was pushed. It's the property of the standing dominoes that decides the speed of the disturbance.
A photon is much the same. It's speed is a property of the space that it passes through, and so is a constant.

The other aspect of the speed of light is the weird fact that, no matter what your motion relative to the photon, you will always observe it's speed to be the the same constant value. Which at first sight is weird. The light is moving at a constant speed, but no matter whether you speed up or slow down, you always will observe and measure the same speed.
The reason for this is that your time speeds up or slows down, as your own motion changes. And because your rate of time is fundamentally linked to your motion and the speed of light, it happens that your time changes in such a way that the speed of light will always look the same to you.

Imagine you're chasing a train on a horse. The train is going faster, and passing you at a rate of three carriages per second. You speed up your horse, so now the train should pass you at the rate of two carriages per second. But, IF your watch slows when your horse goes faster, then one second on your watch is still long enough for three carriages to pass you. So no matter what speed you do, you always measure the train moving past you at three carriages per second.

It happens that way with light because the speed of light is intrinsically linked to the rate of passage of time. So it exactly cancels out the effect of any change in motion relative to the photon.
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Re: Another dumb fisics question.

Post by Brian Peacock » Mon Jan 15, 2018 10:21 am

And from the perspective of the photon, it exists for next to no time at all.
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