Why does light travel at the speed of light? (in a vacuum).

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Offline Airthumbs

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What makes light travel so fast?  Even we emit light in the infra-red, photons, I know, but why are these little packets of photons leaving us with such rapidity...... how many g's are these packets pulling when they go from 0 to light speed, instantly?
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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #1 on: 16/05/2011 16:49:49 »
It only has one speed in a vacuum.  It is born and dies at that speed.  It does not experience any g force as it has no mass.

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Offline Phractality

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Why does light travel at the speed of light? (in a vacuum).
« Reply #2 on: 16/05/2011 17:46:58 »
According to mainstream science, "It just does." They do have a math formula for the speed of light as a function of permeability and permittivity of free space; but those parameters are defined by the speed of light, so the definitions are circular. They say that light requires no medium.

If you can't stomach the idea of a wave with no meadium, ask again in the New Theories section. We're not permitted to share our non-mainstream ideas in the Physics, Astronomy & Cosmology section.
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Offline Bored chemist

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Why does light travel at the speed of light? (in a vacuum).
« Reply #3 on: 16/05/2011 19:34:03 »
"but those parameters are defined by the speed of light"
No, they can be measured independently.
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Offline Geezer

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Why does light travel at the speed of light? (in a vacuum).
« Reply #5 on: 16/05/2011 23:13:55 »
http://www.physorg.com/news/2011-05-when-the-speed-of-light.html    whats this mean?

Well, it's in nitrogen rather than a vacuum for a start. It might suggest that electromagnetic radiation (light) is susceptible to magnetic fields, which might not be a total surprise, but I'd be interested to see if the results are reproducible when the nitrogen is removed.
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Offline JP

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Why does light travel at the speed of light? (in a vacuum).
« Reply #6 on: 17/05/2011 04:12:59 »
http://www.physorg.com/news/2011-05-when-the-speed-of-light.html    whats this mean?

Well, it's in nitrogen rather than a vacuum for a start. It might suggest that electromagnetic radiation (light) is susceptible to magnetic fields, which might not be a total surprise, but I'd be interested to see if the results are reproducible when the nitrogen is removed.

It's not actually all that surprising.  First, f you have a magnetic field in a vacuum, you have energy there, so space-time is warped a bit.  With a very high field, I could imagine that you would have to take into account general relativistic effects, which could delay light in some directions compared to others.  I think in this case this isn't what's happening, though, since the field is uniform...

Second, what I think they're getting at is that at very high energy densities, there are quantum effects even in vacuum where EM fields can interact with each other (something which isn't allowed in classical electromagnetism).  Last I heard, these effects were expected to be so tiny that no one had managed to measure them, so they're purely theoretical.  I suspect they're aiming for this effect, since the last line of the abstract reads:
Quote
We were able to measure a nonreciprocity as small as Δn=(5±2)×10-18, which makes its observation in quantum vacuum a conceivable challenge.

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Offline Phractality

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Why does light travel at the speed of light? (in a vacuum).
« Reply #7 on: 17/05/2011 04:51:14 »
"but those parameters are defined by the speed of light"
No, they can be measured independently.

Quoting from Wikipedia:
Vacuum permittivity
Vacuum permeability

Fc = 1/(4 π ε₀)(q₁q₂/r²)

The value of ε₀ is defined by the formula ε₀ = 1/(µ₀c₀²).

Since μ₀ has the defined value 4π × 10^−7 H m‾¹,[3] and c₀ has the defined value 299792458 m•s‾¹,[4] it follows that ε₀ has a defined value given approximately by
ε0 ≈ 8.854187817620... × 10‾¹² F•m‾¹ (or A2•s4•kg¹•m‾³ in SI base units, or C²•N‾¹•m‾² or C•V‾¹•m‾¹ using other SI coherent units).[5][6]


So c₀ is NOT derived by the formula c₀ = 1/√(µ₀ ε₀). It's the other way around.
 


In some ether-based models, light propagates like an acoustic shear wave in a solid according to the formula cs = √(G/ρ) where K and G are the bulk modulus and shear modulus of the elastic materials, respectively. The density and shear modulus of the ether are unknown, but this formula gives us their ratio and provides a rational explanation for WHY c is what it is. But this in not mainstream science, so don't give this answer on your final exam in college. Go the the New Theories section to learn more about ether theories.
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Offline Bored chemist

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Why does light travel at the speed of light? (in a vacuum).
« Reply #8 on: 17/05/2011 07:19:20 »
Phractality, in that case, the speed of light is what it is because they defined it that way.
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Offline GrapperJ

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Why does light travel at the speed of light? (in a vacuum).
« Reply #9 on: 17/05/2011 20:25:16 »
newbielink:http://zidbits.com/2011/04/why-cant-anything-go-faster-than-the-speed-of-light/ [nonactive] has a decent layman writeup on light speed.

In short, don't confuse the speed of photons with "light speed". Light speed is a maximum limit and a function of reality and space/time itself. Asking why light speed is what it is is like asking why is doesn't our reality have 6 spatial dimensions. It just does. If light speed was different, our reality and universe would also be very different.
« Last Edit: 17/05/2011 20:29:44 by GrapperJ »

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Offline Phractality

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Why does light travel at the speed of light? (in a vacuum).
« Reply #10 on: 17/05/2011 21:18:59 »
Phractality, in that case, the speed of light is what it is because they defined it that way.

Originally, the meter and second were defined in terms of Earth's size and rotation. Earth's polar circumference was 4 x 10^7 meters, and the mean solar day was 86,400 seconds. The meter was then standardized to the length of a certain platinum rod (which turned out to be slightly less than 1/(4 x 10^7) of Earth's polar circumference). We took precise measures of the speed of light using those meters and seconds. As our methods of measurement became more precise, we discovered that Earth's size and rotation are not perfectly constant; meters and seconds change very slightly in proportion to the speed of light. So we changed the definitions of meter and second, making the speed of light 299792458 m/s by definition. So that is how we ended up with that number for the speed of light.

What gave the speed of light that ratio to Earth's size and rotation, in the first place, is still a mystery.
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Offline yor_on

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Why does light travel at the speed of light? (in a vacuum).
« Reply #11 on: 18/05/2011 00:07:30 »
Yeah, It's our foremost constant. But it was a very interesting experiment you found Czarcar

"for the first time, that light does not travel at the same speed in opposing directions in a gas where an electromagnetic field reigns. The measured difference in velocity is around one billionth m/s (i.e. 10-9 m/s, which is equivalent to 10-18 times the speed of light). This infinitesimal difference, predicted by theory, is caused by the magnetic and electric fields."

What that makes me think of is the photons 'momentum' and symmetry, seems like a similar effect to me as the idea of a photons 'recoil'? Then again, we can down convert it if we like to a question of what governs our lives, and there we have the idea of everything carried by 'virtual particles' as the 'force carriers'. Using that definition it is no miracle that a magnetic field can influence the photon, as it is the origin of 'electromagnetism'. And as JP points out, if we go to a quantum plane there is no place without those virtual particles, aka photons in this case.
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Offline Airthumbs

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Why does light travel at the speed of light? (in a vacuum).
« Reply #12 on: 27/06/2011 00:41:36 »
I appreciate all the responses but I am afraid you have all left me, well not entirely satisfied.  [:P]  The best answer I found to my question went along the lines of....."it just is, so don't ask"  and that sounds more like a religious response then a scientific one to be honest.

When people talk about light they say it has a source, that the light is "emitted from that source".  So a massless photon is emitted from a chemical reaction.  Just before the reaction takes place the photon does not exist, it is therefore not moving at any speed at all. 

What I am struggling to get at is, how can it be that at the exact point of existance the photon can only exist at the speed of light.  Does anyone understand my confusion here?  You see for that photon to have a source and if that source is stationary then how can it be instantly travelling at the speed of light, it's just not possible, unless the photon was in existance before that and was always travelling at the speed of light....  [:-\]

Maybe the acceleration of this photon to light speed is happening so fast it is not detectable?  Anyway I cannot accept that photons are "born" at the speed of light.  They only reach the speed of light in our universe because they can and that is the limit.

Recent experiments have succeeded in actually stopping light, Hau's team stopped light for one-thousandth of a second!  This process involves the slowing down of light.  Are you all saying that after this experiment the light just shot off instantaneously at the speed of light?  I'm not having it!  [;D]

Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline yor_on

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Why does light travel at the speed of light? (in a vacuum).
« Reply #13 on: 27/06/2011 04:26:49 »
Well, as I see it there has to be presumptions with any experiment deciding a 'photons path' Airthumbs :) Photons only exist in interactions. You can think of photons/waves three ways, as something 'propagating', as something being a 'constant', as something being the best 'clock' we have.

If you ignore 'propagating' you will still have a constant, and a clock. I can't see any experiment showing us a single photons propagation. The only way to define it practically is by 'weak measurements', and then you fall back on measurements over a large amount of 'photons' defining it as they are not only 'similar', but 'indivisible', which they in fact are not. If they were 'there could only be one' as they say in Highlander. Otherwise it will have to be done theoretically.

As for light only having one 'speed'. It's massless, inertia is defined by mass, so is accelerations. So in a way you can see it as a direct result of light having no mass. without it light has no reason to accelerate as I see it. If we accept the recoil as a definition of 'something' reducing the energy of whatever it is experiencing that recoil, then we can use that as a definition of something 'leaving' or 'disappearing'. And we know that photons annihilate in their final interaction, meaning that all light you see is photons dying. But in between those two states we can't test on a single photon. Any path defined must be a statistical approach, and as confirmed by lights duality we can't even state if it is a photon or a wave in between, as I see it.

So, assuming a propagation, a photon is massless. Assuming no 'propagation' you have two interactions (recoil-annihilation) defined by a constant, that also is a clock.
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Offline Heikki Rinnemaa

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Why does light travel at the speed of light? (in a vacuum).
« Reply #14 on: 27/06/2011 06:27:51 »
 [:)]

Hi.

My opinion is that light does not have constant speed.

I draw image where is two possibilityes,,,A and B,,,and i dont no any natural reasons why light goes like B. But natural function is that A.

Light start to goes speed 0 and accelerate some maximum speed,,,can be more than measured 300000km/s near sun-earth,, and then decelerate,,and enough faraway from light-source light speed is  again 0km/s.

Speed is not constant,,even light is particle or matter-vibration,,it is matter-particle with mass,,but if you think that it is wave-vibration without matter,,i dont agree that because i dont have any needs to say what light is,,it is still and support our life.


 [:)]

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #15 on: 27/06/2011 14:09:16 »
Light start to goes speed 0 and accelerate some maximum speed,
Ok, be Δt the time interval needed to a photon to accelerate from 0 to c, in a specific frame of reference. Now let's make the measurement in another frame, which is moving at velocity v with respect to the first. The time interval is not the same anylonger, it becomes Δt*sqrt[1-(v/c)2]. The final speed, however, is still the same, because light' speed is invariant (= frame independent) so the (average) acceleration is different. Does it make any sense? What if v --> c? The acceleration becomes infinite?

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Offline Mr. Data

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Why does light travel at the speed of light? (in a vacuum).
« Reply #16 on: 27/06/2011 19:47:04 »
As has been mentioned, permitivitty and permeability explain exactly why light travels at the speed it does. However, this speed can be changed depending on the medium, so light for instance would travel slower in a universe where it's vacuum energy density is higher (just as an example) and not that I believe parallel universes exist.

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #17 on: 28/06/2011 07:02:16 »
As has been mentioned, permitivitty and permeability explain exactly why light travels at the speed it does.
And how do you explain the numerical values of those parameters without knowing light' speed? Any measure of them can be traced to a light' speed measure, actually.

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Offline imatfaal

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Why does light travel at the speed of light? (in a vacuum).
« Reply #18 on: 28/06/2011 11:58:28 »
As has been mentioned, permitivitty and permeability explain exactly why light travels at the speed it does.
And how do you explain the numerical values of those parameters without knowing light' speed? Any measure of them can be traced to a light' speed measure, actually.

L-Arrow - are you sure about that?  Whilst most measurements do use the relationship through maxwell's equations - there is no requirement that this is the case.  Nowdays both permitivity and permeability are defined by their relation with the speed of light BUT the wonder of Maxwell's equations is that they can also be calculated without reference to the speed of light
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Offline Mr. Data

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Why does light travel at the speed of light? (in a vacuum).
« Reply #19 on: 28/06/2011 13:05:52 »
As has been mentioned, permitivitty and permeability explain exactly why light travels at the speed it does.
And how do you explain the numerical values of those parameters without knowing light' speed? Any measure of them can be traced to a light' speed measure, actually.

By numerical values, think of the speed of light as a consequence of the permitivitty and permeability of spacetime. You have your light speed, then you know the permitivitty and permeability have exact values. They fit - just like every postulation from Maxwells equation.

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Offline yor_on

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Why does light travel at the speed of light? (in a vacuum).
« Reply #20 on: 28/06/2011 23:43:15 »
You know Imatfaal. Looking at it, it seems as if Maxwell had some twenty equations originally, other sources stating that it was Heaviside that whittled them into their modern configuration? I've tried to look into it but it seems a quagmire to get the history straight there :)

Here's a online version of his book(s) James Clerk Maxwell, A Treatise on Electricity And Magnetism Vol 1 of 2.

But Heaviside interest me a lot. He reminds me of that Russian mathematician that recently refused money and prizes. Both of them seem to have had their own brand of integrity.
« Last Edit: 28/06/2011 23:56:35 by yor_on »
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Offline imatfaal

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Why does light travel at the speed of light? (in a vacuum).
« Reply #21 on: 29/06/2011 11:35:38 »
Maxwell didn't entirely write any of 'his equations'.  (two are Gauss, one Ampere and one Faraday - or is it two Faraday and one Gauss). It is the use, juxtapostion, and fundamental interelatedness of them in his paper On the Physical Lines of Force that means that we call them Maxwell's equations.
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Offline Heikki Rinnemaa

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Why does light travel at the speed of light? (in a vacuum).
« Reply #22 on: 03/07/2011 06:42:44 »
 [:)]


http://en.wikipedia.org/wiki/Electromagnetic_radiation [nofollow]

http://en.wikipedia.org/wiki/Electromagnetic_spectrum [nofollow]


Those all vibration cannot exist pure matterless place,,, and therefore all wave-vibration can--must be matter-vibration,,,

Who says that colors is matter-vibration,,wave-frequence,,,?


Perhaps it is particle speed-motion and particle construction join-movement,,,

- speed
- shape or construction



 [:)]


Live, Love and do Peace.

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Offline JP

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Why does light travel at the speed of light? (in a vacuum).
« Reply #23 on: 03/07/2011 15:46:57 »
Those all vibration cannot exist pure matterless place,,,

Sure they can.

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #24 on: 06/07/2011 20:54:50 »
And how do you explain the numerical values of those parameters without knowing light' speed? Any measure of them can be traced to a light' speed measure, actually.

L-Arrow - are you sure about that?  Whilst most measurements do use the relationship through maxwell's equations - there is no requirement that this is the case.  Nowdays both permitivity and permeability are defined by their relation with the speed of light BUT the wonder of Maxwell's equations is that they can also be calculated without reference to the speed of light
You know tha μ0 is defined from the Ampère (μ0 = 4π*10-7), so it remains ε0. How can you measure it? You shoul for example measure the coulombian force between two charges at a specific distance because of:

F = (1/4πε0) q1*q2/r2

I wonder if it's possible to measure the charges q1 and q2 in Coulomb, without knowing ε0.

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Offline Mr. Data

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Why does light travel at the speed of light? (in a vacuum).
« Reply #25 on: 06/07/2011 21:16:29 »
And how do you explain the numerical values of those parameters without knowing light' speed? Any measure of them can be traced to a light' speed measure, actually.


L-Arrow - are you sure about that?  Whilst most measurements do use the relationship through maxwell's equations - there is no requirement that this is the case.  Nowdays both permitivity and permeability are defined by their relation with the speed of light BUT the wonder of Maxwell's equations is that they can also be calculated without reference to the speed of light
You know tha μ0 is defined from the Ampère (μ0 = 4π*10-7), so it remains ε0. How can you measure it? You shoul for example measure the coulombian force between two charges at a specific distance because of:

F = (1/4πε0) q1*q2/r2

I wonder if it's possible to measure the charges q1 and q2 in Coulomb, without knowing ε0.

Well isn't it apart of the equation, so ask yourself if you pull out the same value.


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Offline Heikki Rinnemaa

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Why does light travel at the speed of light? (in a vacuum).
« Reply #26 on: 22/07/2011 11:49:14 »
Those all vibration cannot exist pure matterless place,,,

Sure they can.

Pure matterless space,,or "room" cannot exist any kind of matter,,
therefore there cannot exist any kind of matter-vibration,,waves,,
and this means that space is full of matter because there can travell radiowaves,,etc.

We known that example space-vehicles can stay on the space one point,,,or we can control motion-direction,,,,why,,because round of this vehicle is matter.

So called ether is,,but what kind is it,,i dont know,,and atom-theory cannot give that answer,,

Of cource i can be wrong,,,:)
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Offline JP

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Why does light travel at the speed of light? (in a vacuum).
« Reply #27 on: 22/07/2011 13:41:35 »
But light doesn't need an aether to propagate through.  The Michelson-Morely experiment in 1887 showed this, and then Einstein later came along and gave us good theoretical reasons why aether doesn't have to exist.  Further experiments have verified both of these results and also shown that while space does have properties that allow light waves to travel through it, these properties are nothing like matter.

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Offline peppercorn

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Why does light travel at the speed of light? (in a vacuum).
« Reply #28 on: 22/07/2011 20:20:32 »
Further experiments have verified both of these results and also shown that while space does have properties that allow light waves to travel through it, these properties are nothing like matter.

That's an interestingly placed 'while' JP. ... It got me thinking: Does matter actually have a property allowing light waves to travel through it?
I mean matter interacts with light-waves, but that is a fundamentally different mechanism isn't it?   In fact, only empty space has that ability  ... Or am I being too philosophical?

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Offline JP

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Why does light travel at the speed of light? (in a vacuum).
« Reply #29 on: 23/07/2011 14:23:18 »
That's an interesting question.  I suppose it comes back to what the definition of a wave in matter is.  Look at another wave: sound.  If sound is traveling through matter, we say it's carried by pressure waves.  But pressure is caused by the interaction of neighboring molecules via the EM force, which transmits even through the empty spaces between molecules.  So in a sense, even sound waves have some component traveling through a vacuum.  Of course, we can look at the big picture and still model a sound wave via pressure variations without worrying about the fine details of the EM forces involved. 

I think for a wave in matter, what we're really looking for is some property of the matter (which need not be a fundamental one) so that you can describe the propagation of energy waves through the matter by a "waving" of this property.  In the case of light in a dielectric, I believe this is polarization of the material.  (I haven't worked through all the details, but I think it plays the same role here as pressure does for sound.)

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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #30 on: 23/07/2011 17:28:06 »
Why does light travel at the speed of light? (in a vacuum).

Photons travel instantaneously, they exist in only the now.  Another way of looking at this is they travel at infinite speed.

How can a photons infinite speed be measured to approximately 300,000 Km per second in a vacuum.  Surely, infinity is infinity?

Let’s take a brief look at time.  What are its attributes?  There is an arrow of time and it can ‘flow’ (be dilated or contracted) at different rates.  At the two extremes time can ‘flow’ infinitely fast (ultimate contraction) or it can ‘flow’ ultimately slow (ultimate dilation) and stop.  ‘Infinitely’ slow (stopped) is a finite  quantity.

Where time stops can be viewed as an absolute.  It is a very similar concept to the temperature of absolute zero.  You cannot go colder, that is where the scale ends.  Time cannot ‘flow’ slower than stopped.

To a photon, the clock has stopped.  It cannot go faster than that.  To do so would require the reversal of time. 

The faster anything moves, the slower time passes (dilates).  This puts an upper limit on speed as ultimately the clock stops.  The same upper limit is reached when viewed from the perspective of energy and mass.

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Offline PhysBang

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Why does light travel at the speed of light? (in a vacuum).
« Reply #31 on: 23/07/2011 17:48:12 »
Why does light travel at the speed of light? (in a vacuum).

Photons travel instantaneously, they exist in only the now.  Another way of looking at this is they travel at infinite speed.
That's no good way to look at them, since we've known since the 1600s that this is not the case.
Quote
The faster anything moves, the slower time passes (dilates).  This puts an upper limit on speed as ultimately the clock stops.  The same upper limit is reached when viewed from the perspective of energy and mass.
This too, is incorrect as far as relativity theory (or any other plausible theory that I know of) goes. Clocks never stop, they only slow in relation to certain sets of coordinates.

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #32 on: 23/07/2011 19:33:49 »
You know tha μ0 is defined from the Ampère (μ0 = 4π*10-7), so it remains ε0. How can you measure it? You shoul for example measure the coulombian force between two charges at a specific distance because of:

F = (1/4πε0) q1*q2/r2

I wonder if it's possible to measure the charges q1 and q2 in Coulomb, without knowing ε0.
Well isn't it apart of the equation, so ask yourself if you pull out the same value.
How do you measure a charge in Coulomb?

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Offline Heikki Rinnemaa

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Why does light travel at the speed of light? (in a vacuum).
« Reply #33 on: 24/07/2011 07:01:30 »
But light doesn't need an aether to propagate through.  The Michelson-Morely experiment in 1887 showed this, and then Einstein later came along and gave us good theoretical reasons why aether doesn't have to exist.  Further experiments have verified both of these results and also shown that while space does have properties that allow light waves to travel through it, these properties are nothing like matter.

Hmm,,Michelson and Einstein make those opionion those days,,because electricity-history was backround of that thinking,,,and of-cource wave-theory,,ant thinking that all light and colors are not matter think,,only wave-vibration like alternative electricity can describe,,,that thought-path was wrong and control science wrong direction,,,many hundred years,,,

Todays we known that light is some kind matter-particle-motion,,, or thouhgt we known :)

Example of moon,,,, moon cannot stay on it's position to round earth if round of the moon dont have any kind on matter,,,basic-space-matter where all this space-planets can floation,,

Some times i have think that this light-particles from sun is that basic matter--but then i change my thoughts,,because less-space opposite moon,,shadow-side has less particle and still moon goes like goes,,

When ether=some kind basic space matter,, is,, then
- planets can floating in this matter
- space-vehicles can drive where we want,,or say one position
radiowaves can go in this matter,,,like sound goes in the air,,

- sound is matter-vibration-motion
- radiowaves is matter-vibration-motion
- without matter both cannot exist

Or i can be wrong still,, still without sun life at earth-ball cannot exist,, space is unknown big area,,:)
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Offline damocles

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Why does light travel at the speed of light? (in a vacuum).
« Reply #34 on: 24/07/2011 15:44:07 »
From lightarrow:
Quote
I wonder if it's possible to measure the charges q1 and q2 in Coulomb, without knowing ε0.

In some circumstances it is, lightarrow, provided you have a reliable value for the fundamental charge in coulomb from Millikan's oil drop experiment or some similar source. You simply count ions or electrons in the particles/devices making q1 and q2. And Millikan's oil drop experiment does not rely on prior knowledge of a value for the speed of light.
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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #35 on: 27/07/2011 06:43:35 »
Why does light travel at the speed of light? (in a vacuum).

Photons travel instantaneously, they exist in only the now.  Another way of looking at this is they travel at infinite speed.
That's no good way to look at them, since we've known since the 1600s that this is not the case.
Quote
The faster anything moves, the slower time passes (dilates).  This puts an upper limit on speed as ultimately the clock stops.  The same upper limit is reached when viewed from the perspective of energy and mass.
This too, is incorrect as far as relativity theory (or any other plausible theory that I know of) goes. Clocks never stop, they only slow in relation to certain sets of coordinates.

It is the way that many people look at them.  I can find no references why this should not be the case.  Would you please quote references to prove otherwise.  No need to go back as far as the 1600s.
From the coordinates of the photon the clock has stopped.  In certain aspects of relativity the clock never actually stops but the trend is the same.  An object with mass can never actually reach the speed of light but the the statement "The faster anything moves, the slower time passes (dilates)" is correct.


"Photons travel instantaneously.
The faster anything moves, the slower time passes (dilates)."

These statements are both true.  Put them together and it explains (as I have done) why the speed of light is what it is and why nothing can go faster than that.



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Offline imatfaal

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Why does light travel at the speed of light? (in a vacuum).
« Reply #36 on: 27/07/2011 10:06:05 »
Mike - please keep this to new theories.
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Offline Airthumbs

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Why does light travel at the speed of light? (in a vacuum).
« Reply #37 on: 29/07/2011 02:31:50 »
I have to honestly say I have read all the responses and I only really understand about 50% of it!!  One thing I might have picked up which has only raised another question is this..... 
If one were able to ride on a beam of light would time stand still in relation to everything else?  We use time as our universal clock but is light itself not subjected to time because of the speed it travels at?


Can someone also please try to explain in English, without funky letters or equations for which I am completely unfamiliar with, why light travels at the speed it does through a vacuum?

PS. I am sure if I asked the same kind of question about the speed of sound through our atmosphere at sea level I would get a response for which I could clearly get my head round but this it seems is something else?  [:-X]
Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #38 on: 29/07/2011 05:51:05 »
I have to honestly say I have read all the responses and I only really understand about 50% of it!!  One thing I might have picked up which has only raised another question is this..... 
If one were able to ride on a beam of light would time stand still in relation to everything else?  We use time as our universal clock but is light itself not subjected to time because of the speed it travels at?


Can someone also please try to explain in English, without funky letters or equations for which I am completely unfamiliar with, why light travels at the speed it does through a vacuum?

PS. I am sure if I asked the same kind of question about the speed of sound through our atmosphere at sea level I would get a response for which I could clearly get my head round but this it seems is something else?  [:-X]

Yes, to both

I think I would be right in saying the mainstream answer is "it just does".
If you find that unsatisfactory you can read my explanation here in new theories.

http://www.thenakedscientists.com/forum/index.php?topic=40322.msg363362#msg363362

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #39 on: 29/07/2011 08:02:33 »
If one were able to ride on a beam of light would time stand still in relation to everything else? 
...and time would stand still for everything else in relation to light. So it doesn't count...

Quote
We use time as our universal clock but is light itself not subjected to time because of the speed it travels at?
Define "subjected to time", because for what I wrote up, it's not clear.

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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #40 on: 29/07/2011 12:58:55 »
If one were able to ride on a beam of light would time stand still in relation to everything else? 
..]and time would stand still for everything else in relation to light. So it doesn't count...


Why doesn't it count?
« Last Edit: 29/07/2011 13:00:54 by MikeS »

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #41 on: 29/07/2011 13:17:10 »
Why doesn't it count?
Because you can't say which clock goes slower than the other, since *both* are seen going slower, from the other: a clock on Earth is measured going slower, from a fast spaceship's frame; the spaceship's clock is measured going slower from the Eart's frame.
I know you are talking of light instead of a spaceship, but you shouldn't, if you want to know what you would see or measure from a very fast frame.

The question:
"If one were able to ride on a beam of light would time stand still in relation to everything else?"

since it's not possible *even in principle* to ride on a beam of light because a frame of reference in which light (in the void) is stationary doesn't exist,
should be interpreted in this way:
"If one were inside a spaceship traveling at almost light's speed with respect (e.g.) to Earth, as near to c as one want, would time go slower for him with respect to Earth?"
The answer is: yes, and time would go slower for Earth with respect to the astronaut.

Twin's "paradox" comes into existence only when one of the two (the spaceship or the Earth) goes back (I make it simple, this is just an example) and they meet again. The one who comes back then is younger than the other.
« Last Edit: 29/07/2011 13:31:06 by lightarrow »

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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #42 on: 29/07/2011 14:48:56 »
If one were able to ride on a beam of light would time stand still in relation to everything else? 
...and time would stand still for everything else in relation to light. So it doesn't count...

I think the sentence is a little misleading as it stands.  If you had written
"from the 'perspective (point of view, reference frame etc.)' of light, time would stand still for everything else in relation to light"  then I would agree it doesn't count.

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Offline Airthumbs

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Why does light travel at the speed of light? (in a vacuum).
« Reply #43 on: 29/07/2011 14:52:54 »
Define "subjected to time", because for what I wrote up, it's not clear.
[/color]


Sorry I don't think I can...  [:P]
Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline lightarrow

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Why does light travel at the speed of light? (in a vacuum).
« Reply #44 on: 29/07/2011 14:54:23 »
If one were able to ride on a beam of light would time stand still in relation to everything else?
...and time would stand still for everything else in relation to light. So it doesn't count...
I think the sentence is a little misleading as it stands.  If you had written
"from the 'perspective (point of view, reference frame etc.)' of light, time would stand still for everything else in relation to light"  then I would agree it doesn't count.

It was what I intended. (But you are answering to me, here, or to Airthumbs?)
« Last Edit: 29/07/2011 14:58:33 by lightarrow »

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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #45 on: 30/07/2011 06:40:29 »
If one were able to ride on a beam of light would time stand still in relation to everything else?
...and time would stand still for everything else in relation to light. So it doesn't count...
I think the sentence is a little misleading as it stands.  If you had written
"from the 'perspective (point of view, reference frame etc.)' of light, time would stand still for everything else in relation to light"  then I would agree it doesn't count.

It was what I intended. (But you are answering to me, here, or to Airthumbs?)

I was answering to you.  "and time would stand still for everything else in relation to light.  So it doesn't matter"

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Offline damocles

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Why does light travel at the speed of light? (in a vacuum).
« Reply #46 on: 30/07/2011 07:21:51 »
One of the main direct verifications of Special Relativity is that unstable particles moving close to the speed of light appear to us to decay slower than they should.

Perhaps a photon has a really short decay lifetime in its own framework, but for us, its time is stopped, so it never decays!

(totally whimsical speculation).
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Offline MikeS

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Why does light travel at the speed of light? (in a vacuum).
« Reply #47 on: 30/07/2011 09:13:54 »
One of the main direct verifications of Special Relativity is that unstable particles moving close to the speed of light appear to us to decay slower than they should.

Perhaps a photon has a really short decay lifetime in its own framework, but for us, its time is stopped, so it never decays!

(totally whimsical speculation).
As far as we know a photon never decays in any time frame, it just 'splats'. [;D]