# Speed Of Light Vs. Time Dilation.

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### #21 ikester7579

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Posted 10 February 2010 - 03:25 AM

It depends on what you mean by this.

Let's imagine that you split yourself into two people, telepathically linked by some sort of quantum entanglement. Any thought AFJ-A has, AFJ-B also has, instantaneously. In this way your two selves can be thought to be communicating.

Now let's imagine that AFJ-A hops on a train that promptly sets off from the station at a relative speed of 0.866c, while AFJ-B remains on the station. Your two selves are going to perform an experiment on how far light travels based on your frame of reference.

I picked 0.866c because it means your relative time dilation would be 2. Every second that passes for AFJ-A, two seconds pass for AFJ-B. Ignore for the moment the fact that AFJ-A's thoughts would become suddenly very comically slurred. When AFJ-A measures the speed of light travelling in the direction of the train's movement (i.e. from the rear of the train to the front of the train), he measures ~300 000 km/s. When AFJ-B measures the exact same photons he will measure... ~300 000 km/s. Intuitively this doesn't make sense: how can an object move two different speeds for two different observers? AFJ-A should have measured C as 150 000 km/s! The answer is in their differing perceptions of time.

Under relativity, there is no universal "now", and there is no universal speed at which a frame of reference moves "future-ward".

Does the preception of light speed remain the same for both people?

### #22 Scanman

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Posted 10 February 2010 - 04:53 AM

Does the preception of light speed remain the same for both people?

Yes

Light for any observer, regardless of what speed they are travelling, will always appear to move at 'c'.

Peace

### #23 ikester7579

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Posted 10 February 2010 - 08:31 AM

Yes

Light for any observer, regardless of what speed they are travelling, will always appear to move at 'c'.

Peace

But if time is moving slower for subject than it is for another, how can it be that it stays the same for both subjects? Is light a supernatural force that controls and bends time?

### #24 skeptic

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Posted 10 February 2010 - 10:12 AM

But if time is moving slower for subject than it is for another, how can it be that it stays the same for both subjects? Is light a supernatural force that controls and bends time?

Thats a bit of a hard concept to grasp. Not light bends space and time but the different speeds of the two observers do this. Space and time is not the same for both because both are in different inertial frames of reference.
The speed of light in a vacuum is the same in all reference frames whereas space, time and simultanety are relative and depend on the speed two observers move relative to each other.

### #25 Guest_TeslaNick_*

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Posted 10 February 2010 - 12:13 PM

The observable universe shows us that the speed of light is the same regardless of how fast you're moving. If you're sitting inside one of those big shipping containers with a flashlight, you measure c as 300 000 km/s. If you're riding a Saturn V rocket hurdling through space at 299 000 km/s, you'll still measure c as 300 000 km/s.

Why? As you move through physical space faster, you move through time slower. Speed is a measurement of distance over time, so if you're perceiving "more time" than a stationary observer, your idea of speed will be distorted by however much "more time" you're experiencing.

Also, there's a difference between light and c (the speed of light in a vacuum). Light can travel slower than c, but relativity still operates according to the theoretical maximum value of c. As I said in another thread, c is maximum speed at which the universe may propagate information over a distance.

### #26 Scanman

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Posted 10 February 2010 - 05:17 PM

Also, there's a difference between light and c (the speed of light in a vacuum). Light can travel slower than c, but relativity still operates according to the theoretical maximum value of c. As I said in another thread, c is maximum speed at which the universe may propagate information over a distance.

Light always travels at 'c', no more, no less. This idea that light can be slowed down is a misconception...what is actually going on is photon propagation. a traffic light event that happens when matter of any kind, is encountered.

The photon always travels at 'c'...when a photon encounters an atom, the photon is absorbed, an electron moves from a stable energy state, to a higher energy state, subsequently the electron shifts back to its original energy state and a new photon (travelling at 'c') is emitted at a specific vector.

It is a relay race, where each runner (photon) always moves at 'c', the baton handoff is atomic absorbtion/emission. It is this handoff that gives the appearance of reduced speed.

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### #27 skeptic

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Posted 11 February 2010 - 06:04 AM

Light always travels at 'c', no more, no less. This idea that light can be slowed down is a misconception...what is actually going on is photon propagation. a traffic light event that happens when matter of any kind, is encountered.

The photon always travels at 'c'...when a photon encounters an atom, the photon is absorbed, an electron moves from a stable energy state, to a higher energy state, subsequently the electron shifts back to its original energy state and a new photon (travelling at 'c') is emitted at a specific vector.

It is a relay race, where each runner (photon) always moves at 'c', the baton handoff is atomic absorbtion/emission. It is this handoff that gives the appearance of reduced speed.

Peace

IÃ‚Â´m sorry to nit-pick here a bit, but the illustration of light propagation through a medium by absorption and reemission is only a simplyfied explanation. If this would be true, light would be scattered in all directions because the reemission is not in the same direction as the light was travelling before, but in all directions.
The slower propagation (or in case of charged materials faster propagation) is a result of the interaction between the electromagnetic field of the photons and the electric and magnetic field permittivity and permeability of the medium, which is a result of the electrons of the atoms of the material.

### #28 Scanman

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Posted 11 February 2010 - 02:41 PM

IÃ‚Â´m sorry to nit-pick here a bit, but the illustration of light propagation through a medium by absorption and reemission is only a simplyfied explanation. If this would be true, light would be scattered in all directions because the reemission is not in the same direction as the light was travelling before, but in all directions.
The slower propagation (or in case of charged materials faster propagation) is a result of the interaction between the electromagnetic field of the photons and the electric and magnetic field permittivity and permeability of the medium, which is a result of the electrons of the atoms of the material.

When a photon hits a medium there is refraction & reflection that takes place...this is the absorbtion/emission process in action.

While a photon exist, it is always travelling at 'c', it is the absorbtion/emission that creates the illusion that light has slowed down....when in reality, light was absorbed and then re-emitted.

There really is no arguing this point, it is basic physics.

Peace

### #29 AFJ

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Posted 11 February 2010 - 06:22 PM

It depends on what you mean by this.

Let's imagine that you split yourself into two people, telepathically linked by some sort of quantum entanglement. Any thought AFJ-A has, AFJ-B also has, instantaneously. In this way your two selves can be thought to be communicating.

Now let's imagine that AFJ-A hops on a train that promptly sets off from the station at a relative speed of 0.866c, while AFJ-B remains on the station. Your two selves are going to perform an experiment on how far light travels based on your frame of reference.

I picked 0.866c because it means your relative time dilation would be 2. Every second that passes for AFJ-A, two seconds pass for AFJ-B. Ignore for the moment the fact that AFJ-A's thoughts would become suddenly very comically slurred. When AFJ-A measures the speed of light travelling in the direction of the train's movement (i.e. from the rear of the train to the front of the train), he measures ~300 000 km/s. When AFJ-B measures the exact same photons he will measure... ~300 000 km/s. Intuitively this doesn't make sense: how can an object move two different speeds for two different observers? AFJ-A should have measured C as 150 000 km/s! The answer is in their differing perceptions of time.

Under relativity, there is no universal "now", and there is no universal speed at which a frame of reference moves "future-ward".

Sorry, but you would think that's too simple an answer for a physicist (lol). So you're saying it's a mental perception then? I'm one, time is a measurement like length or width. We have spacial perception, and we have a perception of time. Events usually mark time. Once an event has passed it's passed. You can't redo it.

I understand there is alot of math which would try to make events occur simultaneously in different dimensions, past, present and future. Now, while I do believe in a spiritual dimension, I have a problem with a coexisting past or future. Otherwise there are an infinity of me and you also.

### #30 Guest_TeslaNick_*

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Posted 11 February 2010 - 06:53 PM

Sorry, but you would think that's too simple an answer for a physicist (lol).  So you're saying it's a mental perception then?

No. As you move faster through physical space, you move slower through time according to outside observers "at rest" compared to you. It's not perceptual, because the effect exists outside of perception--clocks literally slow down if you stick them in an airplane and fly them around the world a bunch of times. When you compare the clock to a stationary ground-based clock, you'll find find that the clock you flew around the world with has registered slightly less time passing. A clock doesn't perceive a length of time than a ruler perceives a measurement of distance.

### #31 skeptic

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Posted 12 February 2010 - 05:34 AM

When a photon hits a medium there is refraction & reflection that takes place...this is the absorbtion/emission process in action.

I donÃ‚Â´t want to derail this thread, because it really doesnÃ‚Â´t add to the discussion here, but this simplified view with absorption and reemission is often told as an explanation for the slower speed of light in matter, even in school and sometimes even in university, because its easy to understand and sufficient for a basic understanding. Its just like the Bohr model of the atom is still explained and used for its simplicity.

Think about it: the discrete energy levels of the electrons in the atom need discrete wavelengths of the absorbed photon. Therefore only a few discrete wavelengths are absorbed and reemitted. Only these would be slowed down if this explanation would be correct. The speed of light in a medium is wavelength dependant but not for discrete wavelengths but continuously over the whole spectrum.

- Your explanation explains only the slowing down of discrete wavelengths, not all of the spectrum
- photon emission of excited electron states are in all directions not in a particular direction
- photon absorption by electron excitation and following deexcitation has always some loss of energy due to heat radiation therefore all transparent materials would have a slight coloured tone not observed in reality.

While a photon exist, it is always travelling at 'c', it is the absorbtion/emission that creates the illusion that light has slowed down....when in reality, light was absorbed and then re-emitted.

Sorry, but this is wrong, plain and simple. And I know even wikipedia tells this that way. The speed of light propagation is dependand on the electromagnetic wave resonance. Light consists of a magnetic and an electric field which could induce a polarization in a dielectric (matter). This polarization defines the "permittivity" of a material. The permittivity is the materials ability to transmit an electric field. Same for the magnetic field and the materials permeability.

There really is no arguing this point, it is basic physics.

Yes, it is. Basic as in low-end for the layman, but in fact incorrect.

### #32 ikester7579

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Posted 12 February 2010 - 07:10 AM

Light always travels at 'c', no more, no less. This idea that light can be slowed down is a misconception...what is actually going on is photon propagation. a traffic light event that happens when matter of any kind, is encountered.

The photon always travels at 'c'...when a photon encounters an atom, the photon is absorbed, an electron moves from a stable energy state, to a higher energy state, subsequently the electron shifts back to its original energy state and a new photon (travelling at 'c') is emitted at a specific vector.

It is a relay race, where each runner (photon) always moves at 'c', the baton handoff is atomic absorbtion/emission. It is this handoff that gives the appearance of reduced speed.

Peace

Hau, 41, a professor of physics at Harvard, admits that the famous genius would "probably be stunned" at the results of her experiments. Working at the Rowland Institute for Science, overlooking the Charles River and the gold dome of the state Capitol in Boston, she and her colleagues slowed light 20 million-fold in 1999, to an incredible 38 miles an hour. They did it by passing a beam of light through a small cloud of atoms cooled to temperatures a billion times colder than those in the spaces between stars. The atom cloud was suspended magnetically in a chamber pumped down to a vacuum 100 trillion times lower than the pressure of air in the room where you are reading this.

She and her team continued to tweak their system until they finally brought light to a complete stop. The light dims as it slows down, so you think that it's being turned out. Then Hau shoots a yellow-orange laser beam into the cloud of atoms, and the light emerges at full speed and intensity.

http://www.news.harv...-stoplight.html

So the light was not going in circles when it stops. It just stops and quits producing light. Of course those at Harvard could be wrong, right?

### #33 Guest_Darkness45_*

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Posted 12 February 2010 - 07:55 AM

http://www.news.harv...-stoplight.html

So the light was not going in circles when it stops. It just stops and quits producing light. Of course those at Harvard could be wrong, right?

Who was saying photons were "going in circles" when it stops (I assume your talking about absorption?)? It is not that it quits producing light, it is light. Just that the light was stopped.

Both Scanman and Skeptic are talking about real phenomena. Electron excitation and deexcitation is real, and is used to explain absorption and emission lines that we see from space. But as Skeptic pointed out, light going through a medium is slowed by the medium's ability to interact with the electric field, not the atoms absorbing and emitting the photons.

### #34 skeptic

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Posted 12 February 2010 - 08:23 AM

http://www.news.harv...-stoplight.html

So the light was not going in circles when it stops. It just stops and quits producing light. Of course those at Harvard could be wrong, right?

The circles you are referring to I think are the ones in a black hole caused by the singularitys ability to warp space-time.
Light stopping or slowing down in a medium is a completely different concept.

What do you think is the implication of these findings?

### #35 ikester7579

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Posted 12 February 2010 - 09:24 PM

The circles you are referring to I think are the ones in a black hole caused by the singularitys ability to warp space-time.
Light stopping or slowing down in a medium is a completely different concept.

What do you think is the implication of these findings?

Implications? That gravity, if strong enough, will pull upon things to be considered to have no mass. Because what we consider as no mass, gravity that strong will make it act like that it does. Actually proving that mass is not always what we think that it is.

### #36 skeptic

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Posted 13 February 2010 - 01:17 AM

Implications? That gravity, if strong enough, will pull upon things to be considered to have no mass. Because what we consider as no mass, gravity that strong will make it act like that it does. Actually proving that mass is not always what we think that it is.

Well, in that experiment you mentioned gravity has no role whatsoever. Gravity canÃ‚Â´t pull on light or photons because they donÃ‚Â´t have a rest mass.
What you interpret as gravity pulling on photons is just the photons following the curved space in what they perceive as a straight line.

### #37 Scanman

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Posted 13 February 2010 - 10:50 AM

I donÃ‚Â´t want to derail this thread, because it really doesnÃ‚Â´t add to the discussion here, but this simplified view with absorption and reemission is often told as an explanation for the slower speed of light in matter, even in school and sometimes even in university, because its easy to understand and sufficient for a basic understanding.

If there is a different 'accepted' model/theory then cite it.

Think about it: the discrete energy levels of the electrons in the atom need discrete wavelengths of the absorbed photon. Therefore only a few discrete wavelengths are absorbed and reemitted. Only these would be slowed down if this explanation would be correct.

Actually the atoms where the quantum energy shift matches exactly that of the energy of the photon will be absorbed and not reemitted...this attenuation shows up as a black band of absorbtion in the spectrum.

This is why it is called the 'absorbtion spectrum'.

The speed of light in a medium is wavelength dependant but not for discrete wavelengths but continuously over the whole spectrum.

Where there is 'any' refraction/refelection then absorbtion/reemission has taken place.

Atoms that are struck at a particular vector will always release (there may be a statistical component here that I am not aware of...Compton scaterring, Feynman QED averages and such) at a distinct vector based on the wavelength/energy of the photon and the quantum properties of the atom.

- Your explanation explains only the slowing down of discrete wavelengths, not all of the spectrum

This is where I must have fallen short in my prior post...

The whole spectrum is handled by absorbtion/emission or absorbtion only...with also the possibility that an average number of photons will make it through the medium on a straight path without encountering any atoms whatsoever.

- photon emission of excited electron states are in all directions not in a particular direction

Photons are reemitted at a specific vector (on average...understanding that there are many things going on of a quantum nature) based on the wavelength/energy of the photon and the quantum energy properties of the atom being struck.

- photon absorption by electron excitation and following deexcitation has always some loss of energy due to heat radiation therefore all transparent materials would have a slight coloured tone not observed in reality.

Basic as in low-end for the layman, but in fact incorrect.

If what is being taught in basic physics is not correct, then please elaborate on what theory is correct and whether it has been accepted by the mainstream physics community.

I admit fully that I am a layman and I am not currently knowledgable enough to work out most of the math, but rely on simplified examples and illustrations.

Peace

### #38 Scanman

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Posted 13 February 2010 - 10:55 AM

I donÃ‚Â´t want to derail this thread, because it really doesnÃ‚Â´t add to the discussion here, but this simplified view with absorption and reemission is often told as an explanation for the slower speed of light in matter, even in school and sometimes even in university, because its easy to understand and sufficient for a basic understanding.

If there is a different 'accepted' model/theory then cite it.

Think about it: the discrete energy levels of the electrons in the atom need discrete wavelengths of the absorbed photon. Therefore only a few discrete wavelengths are absorbed and reemitted. Only these would be slowed down if this explanation would be correct.

Actually the atoms where the quantum energy shift matches exactly that of the energy of the photon will be absorbed and not reemitted...this attenuation shows up as a black band of absorbtion in the spectrum.

This is why it is called the 'absorbtion spectrum'.

The speed of light in a medium is wavelength dependant but not for discrete wavelengths but continuously over the whole spectrum.

Where there is 'any' refraction/refelection then absorbtion/reemission has taken place.

Atoms that are struck at a particular vector will always release (there may be a statistical component here that I am not aware of...Compton scaterring, Feynman QED averages and such) at a distinct vector based on the wavelength/energy of the photon and the quantum properties of the atom.

- Your explanation explains only the slowing down of discrete wavelengths, not all of the spectrum

This is where I must have fallen short in my prior post...

The whole spectrum is handled by absorbtion/emission or absorbtion only...with also the possibility that an average number of photons will make it through the medium on a straight path without encountering any atoms whatsoever.

- photon emission of excited electron states are in all directions not in a particular direction

Photons are reemitted at a specific vector (on average...understanding that there are many things going on of a quantum nature) based on the wavelength/energy of the photon and the quantum energy properties of the atom being struck.

- photon absorption by electron excitation and following deexcitation has always some loss of energy due to heat radiation therefore all transparent materials would have a slight coloured tone not observed in reality.

Basic as in low-end for the layman, but in fact incorrect.

If what is being taught in basic physics is not correct, then please elaborate on what theory is correct and whether it has been accepted by the mainstream physics community.

I admit fully that I am a layman and I am not currently knowledgable enough to work out most of the math, but rely on simplified examples and illustrations.

Peace

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