# Naked Science Forum

## Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: GatoNegroPeludo on 09/09/2012 23:34:38

Title: Why the light travels only a 300,000 kms?
Post by: GatoNegroPeludo on 09/09/2012 23:34:38
I mean, what are the laws that limit the speed of light? Why not faster or slower...
in fact... why does light travel?  :0
Title: Re: Why the light travels only a 300,000 kms?
Post by: waytogo on 09/09/2012 23:48:58
This is another big question,

Well, I guess it's NOT the faster thing in the universe at all.

Also because... why 300.000 km/s?  Ihmo, nobodys was able to determinate such as speed, and: relative to what? and if it's really that, there must be a friction to stop it, but if there is friction, there is resistence, so energy against that ... etc etc.

PS - sorry for my english .. still learning  ::)
Title: Re: Why the light travels only a 300,000 kms?
Post by: Emc2 on 10/09/2012 09:49:01
there are no rules that limit or set the speed of light.  the speed of light is what it is, because that's how fast a Photon travels..

we measured the speed vs our standard measurements, and got the number..
Title: Re: Why the light travels only a 300,000 kms?
Post by: syhprum on 10/09/2012 10:36:08
The speed of Photons depends on the permeability and permittivity of space what determines these ? dark matter or dark energy perhaps it would be interesting if it could be shown to be dark matter as this is not homogeneous which would open up a whole new physics.
Title: Re: Why the light travels only a 300,000 kms?
Post by: lightarrow on 10/09/2012 11:41:29
I mean, what are the laws that limit the speed of light? Why not faster or slower...
"what are the laws that limit the speed of light"
and:
"Why not faster or slower"
are two different questions. The second is quite easy: it depends on the units. It' also 186,282 miles/second or 1,080,000,000 km/hour or 1, or 0.278 in some other units.

If you intended "why it's impossible to travel faster than light's speed in the vacuum" then the answer is That this is the result of experiments and in good accordance with all special relativity; from the principle of relativity it also results that light speed is the same in every inertial frame of reference.
If you intended "why light speed is finite and not infinite" then it's a question for which I don't have an answer.

In any case we should point out that what we know for certain (I mean, experimentally confirmed) about light speed is its "go and back speed", that is the speed in a closed circuit. We are not able to measure light speed from "here to there", for example from here to the Moon; only the speed in the total circuit from here to the Moon and back.
Title: Re: Why the light travels only a 300,000 kms?
Post by: syhprum on 10/09/2012 13:40:43
Why can we not sychronise two clocks one on the moon and one on Earth and measure the transit time of a light pulse or am I running into logical circles ?
Title: Re: Why the light travels only a 300,000 kms?
Post by: CliffordK on 10/09/2012 17:36:55
In any case we should point out that what we know for certain (I mean, experimentally confirmed) about light speed is its "go and back speed", that is the speed in a closed circuit. We are not able to measure light speed from "here to there", for example from here to the Moon; only the speed in the total circuit from here to the Moon and back.
Why can we not sychronise two clocks one on the moon and one on Earth and measure the transit time of a light pulse or am I running into logical circles ?
The problem is that the clocks can loose their synchronization by moving them.  Especially accelerating them at high velocities through different strengths of gravity.  So, once in place one would have to resynchronize the clocks, probably with a pulse that travels at the speed of light.  It then is difficult to separate out the speed of the light pulse used to synchronize the clocks, and the measured speed of light.

A while ago I suggested the experiment be done with geostationary satellites.
One sends a pulse from West to East.
Then 12 hours later when the satellites have orbited halfway around the earth, one sends a pulse from East to West.
The start time of the clocks then drops out of the equation, so there is no need to actually synchronize the clocks.  One just needs to accurately count the time for 12 hrs.

The problem is that all of our clocks are "relativistic".  So, the clock may not in fact tick out 12 hrs perfectly evenly, and the clocks might drift with the different speeds that the satellites are orbiting the planet.  Still it might be a useful experiment to run.

The other option would be to make a pair of mechanically connected shutters, which I believe is also possible, but the tolerances are pretty extraordinary which are required to get 5 digits or so of accuracy which would likely be required to find a difference in the one-way speed measurements.
Title: Re: Why the light travels only a 300,000 kms?
Post by: lightarrow on 10/09/2012 18:46:42
Why can we not sychronise two clocks one on the moon and one on Earth and measure the transit time of a light pulse or am I running into logical circles ?
CliffordK has already answered you, but I want to tell you another way.
You can synchronize two distant clocks in essantially two ways:
1. Using something of which you know exactly its speed, for example light speed, but of course you can't here, light speed is what you want to measure [:)] The standard method is "Einstein synchronization".
2. You can synchronize two close clocks and then transport one of them far away, but you should do it slowly, to avoid relativistic effects, inertia, ecc. This is called "slow transport synchronization".

Someone (not me [:)]) proved that "slow transport  synchronization" is equivalent to "Einstein synchronization".

Einstein synchronization is the simpler method you would use with light:

if you have a distant clock B at a distance "r" from your clock A, you would send, at t = 0, a short light pulse from A to B; B is programmed to set his time at r/c when it receives the pulse.

Example: r = 384,000 km.
When clock A signs 00:00:00 (mm:ss:hshs, where hs means hundredth of second), it sends a pulse to clock B; when B receives the pulse, its time will be set at t = (384,000 km)/(300,000 km/s) = 1.28 s = 00:01:28.
Title: Re: Why the light travels only a 300,000 kms?
Post by: Phractality on 11/09/2012 06:52:45
It is tempting to say that the permeability and permittivity of free space determine the speed of light, but that is circular logic. The truth is their values are defined in terms of the speed of light. You can derive the speed of light from the definitions of permeability and permittivity, not by the measured values of those parameters.
If there is an aether, it stands to reason that its acoustic properties determine the speed of light. There is a formula for the speed of acoustic shear waves in a solid, determined by the shear modulus and inertial density of the solid. For that formula to apply to the speed of light, the aether would need to be incredibly dense and incredibly stiff. At least, it is incredible to most scientists, but not for me. I believe there is an aether; its inertial density must be many orders of magnitude greater than that of a neutron star, and it is comparably stiff.
There is a unique reference frame which is stationary relative to the aether, but that does not make it measurably different from any other reference frame, unless there are observable faster-than-light phenomena. The existence of an aether has not been disproven; it has merely been made irrelevant, so long as there are no observable FTL phenomena.
Title: Re: Why the light travels only a 300,000 kms?
Post by: lightarrow on 11/09/2012 12:18:53
It is tempting to say that the permeability and permittivity of free space determine the speed of light, but that is circular logic. The truth is their values are defined in terms of the speed of light. You can derive the speed of light from the definitions of permeability and permittivity, not by the measured values of those parameters.
Correct.
Quote
If there is an aether, it stands to reason that its acoustic properties determine the speed of light. There is a formula for the speed of acoustic shear waves in a solid, determined by the shear modulus and inertial density of the solid. For that formula to apply to the speed of light, the aether would need to be incredibly dense and incredibly stiff. At least, it is incredible to most scientists, but not for me. I believe there is an aether; its inertial density must be many orders of magnitude greater than that of a neutron star, and it is comparably stiff.
There is a unique reference frame which is stationary relative to the aether, but that does not make it measurably different from any other reference frame, unless there are observable faster-than-light phenomena. The existence of an aether has not been disproven; it has merely been made irrelevant, so long as there are no observable FTL phenomena.
I don't know anything about what you say of that kind of aether; however I don't understand how can light speed be independent of the inertial frame of reference, if a privileged frame for light existed.
Title: Re: Why the light travels only a 300,000 kms?
Post by: Phractality on 11/09/2012 17:51:47
I don't know anything about what you say of that kind of aether; however I don't understand how can light speed be independent of the inertial frame of reference, if a privileged frame for light existed.
Time, distance and speed may be measured relative to the motions of electrons around their nuclei. In a hydrogen atom's own reference frame, those motions are spherically symmetrical. In a different reference frame, the electrons travel farther for each orbit; so they are squashed into an ellipsoid and take longer to complete each orbit. The length contraction and time dilation are determined by relative motion between the observer's frame and that of the atom. The atom's motion relative to the aether is irrelevant.

Matter which is stationary relative to the aether looks no different than matter which is stationary relative to any other inertial reference frame. Theories which suggest otherwise involve swirling or dragging motion of the aether caused by the presence of matter. (If matter, itself, consists of waves moving thru the aether, there is no good reason to suppose those waves should drag or distort their own medium. To expound upon that idea, I would have to introduce new theory, and this is the mainstream forum.)

The reference frame of the aether is not privileged unless there are observable FTL phenomena. In SR, time depends on location parallel to the line of relative motion.
t' = γ(t-vx/c2)
So events at different locations can't be simultaneous in every reference frame.

Some scientists claim to have observed instantaneous transfer of quantum entanglement data across significant distances. If that is verified, it can only be instantaneous in one preferred reference frame; otherwise, you would have all sorts of paradoxes, like hiring a hit man to kill your grandfather before he meets your mother.

Suppose the quantum entanglement phenomenon is instantaneous in the reference frame of the aether. Then in another reference frame, the information may arrive before it is sent in the direction of travel relative to the aether, but information sent in the opposite direction would arrive after it was sent. The round trip of data could be instantaneous in any inertial reference frame, regardless of the reference frame's motion relative to the aether. This does not imply any paradox.

Mainstream science insists that, even if quantum entanglement does transfer data instantaneously, it cannot be used for instantaneous communication. The transfer of data can only be verified after a speed-of-light delay. I don't know if that is true or not. What I am saying is that, if you can verify after the fact that data was transferred instantaneously, then you will have proven the existence of a preferred reference frame.

If that is the reference frame of the aether, then the aether will have been shown to have the property of immobility. In his Leyden Address (http://www.aetherometry.com/Electronic_Publications/Science/einstein_aether_and_relativity.php), Einstein said,
Quote
It may be added that the whole change in the conception of the Aether which the Special Theory of Relativity brought about, consisted in taking away from the Aether its last mechanical quality, namely, its immobility.
Restoring the property of immobility to the aether would strongly suggest that it is a mechanical substance and not just a mathematical entity. I strongly recommend reading that whole address. It debunks the popular notion that Einstein abandoned the concept of an aether, though he agreed that no adequate description of the aether had yet been devised.
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 14/09/2012 05:39:37
Well, to measure a speed you will need to have a distance, in a flat space preferably meaning without gravity. Then you need a way to either synchronism those clocks measuring it, or you will need one clock and reflections. The problem is in how to synchronize those clocks. It becomes no simple thing and you will have to make allowances for 'motion' as well as 'gravity'. The easiest way is the reflected light using one clock. Start ticking as I send it off, stop when it is reflected back. That way there is no, or very little time dilation acting on that clock, what may make it wobble is the relative motion we have and the influence from other gravitating bodies as I think, but that's not noticeable as a guess. Light is very quick and the distances we measure short in a two way experiment.

The time dilation i speak of here is the one relative the light, assuming a light propagation. You can treat it as two observers, one being the light, the other being the clock. And so we get comparisons between 'frames of reference'.
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 14/09/2012 05:52:42
And yes Phractality. If we were to find a 'substance' that bound all heavenly bodies together, not 'space' but something? Then we would have a 'joined' SpaceTime. But the only thing I know of binding our histories together is light, and? Can you use that as aether?
Title: Re: Why the light travels only a 300,000 kms?
Post by: CPT ArkAngel on 14/09/2012 06:00:12
The speed of light is the speed of time...? Locally it is invariant...
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 15/09/2012 01:25:49
Yeah :) locally it is a invariant, as measured by particles interacting, as well as biological systems. If it wasn't 'time dilations' would be noticeable inside your local frame, by you, but they aren't. But it is also a question about what a local frame of reference should be defined as. The best way I've found is to define it to Plank scale. And as I think, as 'time' and 'contractions' leave no physical evidence in us, meaning that we're all sort of 'pliant' when it comes to those, we can accept both contractions and time dilations in ourselves without worrying. Especially considering that we're defining it to the limit of what we can describe if so, and that those tiny effects will be unmeasurable at our current technology, as I know?
=

We do age though :)
And length exist.

One more thing though, we better consider this a (local) arrow, with 'time' being a description relating to something more unexplainable, depending on definitions. The arrow is simple, time is not.

All defined by frames of reference, mediated by radiation.
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 15/09/2012 01:47:31
Maybe it could be measurable over astronomical distances though? That has to do with how to define a SpaceTime.

On the other hand, what interacts with you have only one Plank distance to travel, as I think of it, in my number space :) Because the light you see exist defined through the recoil noticed, and in its subsequent annihilation. And if defining it to Planck scale then the step taken between 'frames of reference' by light can only be one seen as one Plank length. Which undoubtedly becomes a weird definition :)
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 15/09/2012 02:15:55
To see how I think there you need to introduce a 'static universe' first. Then exchange 'motion' for something changing a value in a four dimensional grid, of Planck sized points. Each of those points have four degrees of freedom, length, width, height, and the arrow defined locally as 'invariant'. the three first represent the 'contractions', the last represent 'time dilations' as described between frames. Then you may need some property more 'keeping count' at the values changing in a direct fashion, as all points will have different values, depending on observer (frame of reference), that is, if you want a 'joined, same for all existing simultaneously SpaceTime. It becomes a rather tricky universe, or simple if you only define it from locality. The first one is a description of a what I think would be needed for a 'indivisibly same SpaceTime', as we expect normally. By instead using locality I define it so as we all get our SpaceTime coherence by the constant 'c', as in that radiations 'speed'. Light becoming what join my observation to yours. And in the end it becomes a question of what one then would mean by 'degrees of freedom' as it seems now :) But I really need to consider if this is a valid alternative definition.
Title: Re: Why the light travels only a 300,000 kms?
Post by: myself on 20/09/2012 06:08:01
Light could suddenly change velocity by a factor of a million and its measured speed would not change.  It is the ratio between time and any direction in space, so its proper velocity is 1.  Clocks rely on electromagnetism, after all.
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 20/09/2012 06:11:36
Yes, light is what defines our existence as far as I can see.
Title: Re: Why the light travels only a 300,000 kms?
Post by: wolfekeeper on 20/09/2012 18:49:00
IRC it's been shown that the speed of light isn't fundamental.

What's fundamental is causality.

If the speed that things happened varied in weird ways over the whole of space, provided it preserved the causal ordering we see, you wouldn't notice anything at all.
Title: Re: Why the light travels only a 300,000 kms?
Post by: CPT ArkAngel on 21/09/2012 01:58:09
Where is that proof Wolfkeeper?

In my opinion, it is certainly a circular argument demanding a unified theory to get out of the loop. And i don't see the relation with causality. There is no contradiction between causality and the speed of light being fundamental...
Title: Re: Why the light travels only a 300,000 kms?
Post by: yor_on on 22/09/2012 18:26:33
You could say that causality is a fundamental property for macroscopic systems Wolf, at least that is the way I see it. And causality is defined by the arrow. What one can state from such a reasoning is that we nowhere should be able to see the arrow go backwards, looking 'out' at such a universe. That means that even though you have frames of reference behaving oddly, if defined by your clock and ruler, slowing or speeding you will never find another frame ticking backwards.

But that view meets its limit at QM in where you have statistics and probability taking over. And one should not forget symmetries. It seems as if the universe really is 'one thing' both macroscopically and microscopically, in that you can by transforming something into another symmetry group find it to behave differently, expressing new properties but following a pattern of symmetry, as I think of it. But you can also ask yourself from where you take your measurements, and what then defines the universe you observe?

Locally there are no doubts, we all find a same arrow, and a same ruler, always. But when comparing between frames of reference you will tell your neighbor that his measurements must have changed, even though he doesn't notice it. And he might say just the same about your measurements, no matter who introduced change as in a acceleration. So where is the pivot from where we define worlds to turn?

Locality.