Einstein's special theory of relativity

Einstein's special theory of relativity says that "the speed of light is constant at c=3.00x10^8 m/s, relative to ALL inertial frames of reference"

I don't quite get this part. Any reason or easy proof on its constancy? Why is it violating the common concept of relative velocity?

For example, using relative velocity concepts, if a spaceship is travelling at 2x10^8m/s in the direction of the light. A person inside this spaceship should measure this light has a speed of 1x10^8 m/s. But such is not the case??

 

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Hi kingwinner,
The reason is related to Maxwell's laws of electrodynamics. Maxwell's laws imply a speed for the propogation of electromagnetic radiation. This poses a problem - a speed relative to what?

Several experimenters attempted to find the base reference frame in which EMR propogates at c, but it always seemed to be undetectable. Read some historical perspective here. Found on Reflections on Relativity.

Einstein's theory of relativity (the special theory) proposed an explanation for these odd experimental results. He proposed that such a base reference frame does not exist - that EMR propogates at c in all inertial reference frames. He then examined the consequences of that proposition, and found some strange results, but no inconsistencies.

I think the real question is "Why does the common concept of relative velocity exist if the Universe doesn't actually work that way?"
The answer is that at low speeds (compared to c), the rules of the Universe are indistinguishable from the common concept of relative velocity.

There are no easy proofs of relativity because of the high speeds involved. The Michelson Morley experiment is perhaps the most famous. The most common proof would be any experiment performed in an atom smasher (cyclotron or linear accelerator). You might get a chance to play with one if you do post-grad nuclear physics, I think. (I don't know myself, I'm a business graduate

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Hi,Pete,

Consider a ball moving foward inside a bus. Say, the ball is moving at 10m/s relative to the bus and the bus is moving at 30m/s relative to the earth in the same direction. The ball's speed relative to the earth is then 40m/s, but the ball's speed is only 10m/s relative to the bus. Why is light so special that its speed is absolute and has no relative velocity?

 

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This is because velocities don't actually add linearly (this is one of the strange consequences that Einstein found as a result of proposing a frame independent speed of light).

According to the special theory, if the bus is moving at speed v relative to the ground, and the ball is moving at speed u relative to the bus, then the ball is moving at speed w=(u + v)/(1 + uv/c&sup2

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relative to the ground.

So if the bus is moving at exactly 30m/s and the ball is rolled at exactly 10m/s relative to the bus, then the ball's speed is 39.99999999999987 m/s relative to the ground. You can see why velocity addition looks linear at low speeds!

For the case of light, u = c, which means that no matter what v is, w will always be c as well.

 

The phenomena of relativity is real and SR works to describe it. Back in 1909 a fellow named H. Ziegler proposed a true cause for the phenomena. His concept produced all the phenomena but in classic space-time. His concept never caught hold, but it works just as well to explain relativity as our current concepts do.

edit: Just thought this might be relevant for anyone who has trouble with the variable space-time concept.

 

Hi Vern,
I'm sure Ziegler's work is very interesting... but it's not what kingwinner is looking for.
I can't actually find anything concrete about Ziegler's work. Is it fringe science?

 

Ziegler was positioned well enough to be present at the conference but I haven't seen further work he did along those lines. It interested me because he presented the answer to the puzzle of the root cause of relativity a hundred years ago. Ziegler was probably referring to the work of Lorentz. Lorentz tried to show how the final irreducible constituent of all physical reality might be the electromagnetic field. Lorentz did not succeed in this but his efforts brought him fame for the great truths he did discover.

 

The common concept of 'relative velocity' is derived from the spatial relationships between ordinary (material) objects and can not be applied to light signals. Einstein tried to get around this by nevertheless applying the usual concept of 'speed' to light signals, and then re-scaling his length and time units in order to formally achieve a constant speed of light. He did apparently not notice that it is the concept of 'speed' and not of time and space which has to be revised in the context of light signals (see my page Speed of Light and Theory of Relativity for more).

Thomas

 

Einstein used the only definition of speed I'm aware of: namely the classic speed=distance/time. What reengineering of this definition do you think he should have used?

He didn't just rescale the units so he could claim c was invariant; he proposed that all the fundamental laws of physics took the same form in these rescaled reference frames, which would necessarily imply that measuring instruments and observers would scale in the same way. As a consequence, any measurements of a speed in such a frame would be affected by this scaling. All that's left is to decide whether this should be considered reality (the Relativity view) or an illusion caused by distorted equipment (the Lorentz Ether Theory view). The former is generally preferred as the latter implies an undetectable absolute frame that can have no effect on physical measurements.

 

Well put. It should be noted that the SR view is generally prefered over LET only for philosophical reasons (e.g. Occham's razor which, IMO, is a very good principle). It is not possible to choose one over the other on the basis of logic (they are both internally consistent) nor experiment (they both predict the same experimental results in all cases).

I generally prefer the SR view, but I shamelessly use the LET view when it is convenient or aids my personal understanding, such as when thinking about Doppler.

-Dale

 

The big plus for the LET view is that it keeps classic space-time intact while still providing relativity phenomena. When you accept that there might possibly be an at-rest point of reference, that occupied by the background radiation would be an immediate candidate. I suspect that there may be something that could prove this, but have no idea what it might be right now.

(edit): The fact that the background radiation does occupy a frame of reference all its own should have some significance !

 

Hi Vern. This could be worth discussing, but not to hijack kingwinner's thread. If you want to continue it in a new thread, perhaps you could begin by naming the conference you mentioned and the presentation that Ziegler gave? A link to the proceedings would be great, but I doubt that it exists online.

 

Hi Pete; you're right; I didn't mean to hijack kingwiner's thread. I'll read the conference papers again and see if I can scan them into an OCR and link to it in a new thread.

 

Monkey business.

 

I think I learned this reading one of your posts.

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Obviously a definition that does not depend on the velocity of source or observer at all, i.e. one that depends only on the distance x between both at the moment the signal is emitted. So if the light signal is emitted at time t=0, the travel time to the observer is T= x(0)/c regardless of the relative velocity between the two. This is in fact obvious if you put yourself in the position of the observer: any velocity of the source can not affect the travel time given the invariance of c in this respect; the travel time is only determined by the location of the emission.

See my page Speed of Light and Theory of Relativity for an elaboration on this.

Thomas

 

Kingwinner,
As you may have discovered there is a continuing debate/discussion regarding the validity of Einstein's theory of relativity. The very best source of Eisntein's theory is the discussion in Einstein's book, "Relativity", written ten after his 1905 paper which was written in German and accepted by the non-German speaking world on faith, mostly.

As one example only, Einstein claimed that he was unaware of the Michelson-Morely experiment conducted in 1887 in Geremany. This is most difficult to believe as a true statement as this experiment had placed the physics world in a quandry, to say the least. MM was familiar to virtually all physicists with any interest in the subject matter.

The MM experiment is usually discussed in terms of its 'null' effect when no such 'null' resulted. MM found an 8km/sec absolute velocity which was conbfirnmedd by Dayton Miller in over 300,000 reproductions of the MM experiment over the next three decades. The 8 km/sec speed is greater than 1/4 of the assumed orbital motion of the earth around the sun, hardly a "null' result, do you agree?. However, consider that the sun was found to be in motion at approximately 211 km/sec, no one has explainmed how this velocity was separated from the earth orbital velocity during the experiments. Likewise, the triangular trajectory assumed in the transverse light pulse is contrary to the postulate regarding the indepedence of light motion. This indepenxcence states that the motion of light, the speed of light, is independent of the motion of the source of light. Einstein, in chapter VII in 'Relativity', substituted light motion for the motion of a man walking on the train, certainly in violation of the independence postulate.

Don't be quick to assume the validity of committed SRT theorists whose entire career and belief system is shattered by a wide spread and ever increasing, discarding of the silliness of SRT.

Any persons who is unable to come to a definitive understanding of the parameters included in the 100 year debate regarding SRT is in the wrong business.

Check it out.

Pete is grossly in error, grossly.

Einstein made the assumption that the statement that the laws of physics for the motion of light means that the measuremnt of the relative velocity of frame and photon must be the same measured in all inertial frames of reference. This is a sham substitution of 'speed oflight' for 'relative speed of frame and photon'.

This is Einstein's sham statement offerred to the reader without any physical justification.

I have included a post written in response to Neddy Bate's discussion immediately preceding the response. You may read the last few discussions between Nedy Bate and myself as we both focussed on Einstein's assumptions and reasoning used in developing SRT as expressed in "Relativity".

Likewise, the SAGNAC effect is a must research project for anyone critically examining SRT. Google on 'saganac effect' will get you started.


[post=1114696]Try this and the few preceding discussions for a negation of Einstein's SRT[/post]

Geistkiesel ​

 

And the crackpots have arrived. You'll get used to them if you bring up any relativity questions, kingwinner.

They're not all bad - they're great for polishing your critical thinking skills.

 

The Sagnac effect is predicted by both SR and classical mechanics. So its existence hardly constitutes evidence against SR.

-Dale

 

By the way Kingwinner, I had the following thoughts in response to your original question (maybe to un-hijack the discussion).

If there really is no ether and EM waves propagate in perfect vacuum then it seems to me that c must be constant. After all, what speed does the vacuum have in any frame of reference? With sound waves the speed of the air is something that exists in any frame and is frame variant, so it makes sense that the speed of sound should be frame variant. But perfect vacuum is not like that, you cannot really assign it a speed in any frame, so how could c vary in the same manner that sound does?

Obviously, that is not a rigorous proof, but maybe it will help.

-Dale