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/sci/ - Science & Math

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3887267 No.3887267 [Reply] [Original]

Can someone explain how if light travels through water it slows down, but when it exits water it exits at the speed of light? How is this possible?

>> No.3887281

light doesnt slow down in water, it bends.

>> No.3887292

She's not going in a straight line.

>> No.3887306

>>3887292
must you fuck up every thread on sci?

>> No.3887302
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3887302

light never slows down. For instance, light passing through a diamond bounces around due to the structure of diamonds and appears to become slow down while inside.

>> No.3887330
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3887330

>>3887306
Why do you say these things. Krakengineer is a pretty decent tripfag.

>> No.3887349

>>3887302

can you explain why if you are traveling at 50% the speed of light, you still observe light passing you at the full 100% speed?

>> No.3887368
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3887368

>>3887349
I actually can't - but here is some reasoning off the top of my head.
The speed of light is the infinite or limit of speed. If you stand at the middle of a numberline that ranges from 0 to infinity no matter where you stand - you still perceive infinite in front of you.
In the same way no matter how fast you are going light will always be the limit of speed.

>> No.3887383

>>3887368

Some scientists have actually accelerated neutrinos faster than the speed of light.

>> No.3887400

>Is it possible to slow light down?

>The short answer is No. Einstein's theory of special relativity is based on the idea that the speed of light is always constant. However, we CAN make it take longer for light to travel a set distance. In fact, we say that light travels more slowly in optically dense media. That statement is somewhat misleading. We need to look into the physics of the phenomenon.
http://www.physlink.com/education/askexperts/ae509.cfm

But that explanation is an oversimplification as well.

>> No.3887672

i saw in paper some guys fired of particles faster than speed of light. i wonder if earth directional speed and rotation was taken in to account? if they fired the beam in the opposite direction the earth was moving then wouldn't that have an effect of moving the finishing line closer to the start? (imagine standing on a moving train and you through a ball to your partner toward the back- in reality the ball would inherit the trains momentum eliminating this effect of the fact the end is moving toward the ball and is why you can stand up on one so long as you were in contact with in when its moving at 200mph. but if the speed of light is absolute and not able to be slowed down or sped up via source speed inheritance then it would act like the ball was thrown from a station platform from the trains front and aimed at its end- which if the train is moving would be closing in on the ball to meet it prematurely. the space is thus compressed and you didn't make one black hole to do it!

>> No.3887706

>>3887349

There is no such thing as "traveling at 50% the speed of light." All motion is relative. In your own reference frame, your velocity is always zero, and light always moves at C. In some other reference frame you might be moving at .5C, but that's not what you yourself experience.

>> No.3887775

>>3887383

No.

>> No.3887778

>>3887383

Too bad, it's definitely only an error in calculation. They haven't released any solid proof yet. The media got your brain in a knot.

>> No.3887845

>>3887778
you are wrong good sir, Einstein was a dumbass and was wrong, relativity, general and special, is a dumb wrong theory

>> No.3889363

Is everyone here stupid?!

1) The speed of light is NOT infinite. Light in a vacuum (c) is a set speed. Light through other mediums can be calculated (just as had been done with sound)

2) There is enough hard evidence that people at CERN have been able to send a few thousand particles faster than the speed of light by calculating the time they took to fly a certain distance and the time it took them to get there.
It's been pretty big on this board the past few weeks.

>> No.3889385

light is ALWAYS traveling at the speed of light

the speed of light in a material appears longer because the light is being absorbed and re-emitted by particles within the material.

>> No.3889394

light isn't something that acts like normal matter, you can't think of it like that. I mean, have you every taken the time to understand particle-wave duality?

Long story short: No matter what your reference frame is, light will be traveling at C compared to it. Light doesn't ever slow down. It can bounce around, its' path can be bent, etc, but it doesn't slow down.

>> No.3889401

the velocity of light is reduced in water but not the speed.
light moves at the same speed in any medium, it just bounces around in denser mediums like waters.
this means it tends to take longer to get from point A to point B (generally on a macro-scale) under water.

>> No.3889427

>>3889401
>>3889385
doesn't this imply the speed of light in a medium varys since the interaction of photons with the particles within a medium are probabilistic?

i.e. if i shined light through some water, some photons would be seen on the other end with a speed around c, the most around the "speed of light in water", and some slower then that speed? like a normal distribution centered on "speed of light in water", but unlike a normal distribution because no values higher then c would be seen (whatever you would call this, idk, truncated normal distribution?)

>> No.3889464

Wow, I was not expecting to see the correct answer to this. :)

All I can add is that absorption/emission simply adds a phase shift of pi radians to the light wave (giving the delay).

>> No.3890690

>>3889394

But how can light always be going the speed of light faster than you? it dosnt make sence, if you are going 90% the speed of light, light should appear to only go 10% the speed of light past you RIGHT? HOW can it possibly appear to go 100% the speed if you are going 90% c

>> No.3890707

>>3890690
that's what the theory of RELATIVITY explains
hint: observations are RELATIVE to the observer

short answer: there is no absolute time... it's measured differently by different observers, which explains all the apparent contradictions of relativity

yeah, it seems fucking batshit insane at first, but when you actually understand the math it makes sense

fucking Lorentz transformations, how doe they work?

>> No.3890758
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3890758

>>3887267

>> No.3890803

>>3890707

>doe

get the fuck out.

>> No.3890812

>>3890690

If you go near the speed of light, time slows down for you. The light passing you as you go 90% the speed of light, will be traveling faster and in a way break through time, from your perspective.

That's why the speed will always be the full speed of light.

>> No.3890827

Disregard my post, I love EK.

>> No.3890870

>>3887330
hes alright, but he has his moments too
http://archive.installgentoo.net/cgi-board.pl/sci/thread/3886863
lol

>> No.3892511

>>3890812

but there is no proof for this

>> No.3892537

>>3892511

0/10
Not convincing enough. Try again later.

>> No.3892552

I don't know, but I might take a course on this type of stuff in spring. Make a new thread then.

>> No.3893368

>>3889427
looks for an answer to this..

>> No.3894864

>>3890812
>>3892511
>>3892537

OP don't listen to this retard.

Listen to these retards:

>>3887706
>>3890707

>> No.3894881

>>3889427

I guess. Does this introduce problems for you or something? As long as you start off with the premise that light is interacting with matter in a non-vacuum through diffraction and shit and not actually slowing down, you're A-OK.

>> No.3894882

then explain Cherenkov radiation motherfuckers.

>> No.3894896

>>3887383
I'll start even paying attention to this neutrino shit when the results have been duplicated. Which they almost certainly won't be.

>> No.3894921

>>3894882

Different conversation require different levels of abstraction. To discuss Cherenkov radiation requires a much lower level of abstraction of the propagation of a light wave.

Here's what happens when light travels through a medium:


In addition to propagating through a vacuum, light may also propagate through many types of matter, denoted as the medium. Light traveling within a medium is no longer a disturbance solely of the electromagnetic field, but rather a disturbance of the field and the positions and velocities of the charged particles (electrons) within the material. The motion of the electrons is determined by the field (due to the Lorentz force) but the field is determined by the positions and velocities of the electrons (due to Gauss' law and Ampere's law). The behavior of a disturbance of this combined electromagnetic-charge density field (i.e. light) is still determined by Maxwell's equations, but the solutions are complicated due to the intimate link between the medium and the field.

Understanding the behavior of light in a material is simplified by limiting the types of disturbances studied to sinusoidal functions of time. For these types of disturbances Maxwell's equations transform into algebraic equations and are easily solved. These special disturbances propagate through a material at a speed slower than c called the phase velocity. The ratio between the phase velocity and c is called the refractive index or index of refraction of the material. The index of refraction is not a constant for a given material, but depends on temperature, pressure, and upon the frequency of the (sinusoidal) light wave. This leads to an effect called dispersion.

>> No.3894933

>>3894921

Aaaaand here's how it ties in to Cherenkov radiation:


Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (electrically polarizable) medium with a speed greater than that at which light would otherwise propagate in the same medium.

Moreover, the velocity that must be exceeded is the phase velocity of light rather than the group velocity of light.

As a charged particle travels, it disrupts the local electromagnetic field (EM) in its medium. Electrons in the atoms of the medium will be displaced, and the atoms become polarized by the passing EM field of a charged particle. Photons are emitted as an insulator's electrons restore themselves to equilibrium after the disruption has passed. (In a conductor, the EM disruption can be restored without emitting a photon.) In normal circumstances, these photons destructively interfere with each other and no radiation is detected. However, when a disruption which travels faster than light is propagating through the medium, the photons constructively interfere and intensify the observed radiation.
A common analogy is the sonic boom of a supersonic aircraft or bullet. The sound waves generated by the supersonic body propagate at the speed of sound itself; as such the waves travel slower than the speeding object and cannot propagate forward from the body. Instead they form a shock front.

In a similar way, a charged particle can generate a photonic shock wave as it travels through an insulator.

>> No.3894997

>>3894933
>>3894921

I guess that makes enough sense. I still feel like I only understand enough to okay.jpg and move on. It's hard to picture a 3-D electromagnetic field when it comes to the propagation of light and its interaction with matter, not even talking about how electrons can "ride the wave" to form "photonic shockwaves".