Albert Einstein contradiction?
skylight
Posts: 1,915
Having just watched a programme about Einstein mentioning how he stated that light speed is a constant and time was not got me thinking of how the speed of light could be a constant if a component of speed is not constant ie time?
I know experiments prove his theories but I am confused by the above
I know experiments prove his theories but I am confused by the above
Comments
-Tor
Are you saying that light is constant but only relatively? if that is the case then the definition of constant cannot apply to all situations.
If that is the case then I dont see how something can be called a constant. but as speed is worked out by time how can the "speed" of light be a constant?
The missing link here is length contraction. The ratio of the two times (time/proper time) is equal to the inverse ratio of the associated measured lengths. Look up Einstein's thought experiment with the railway car - it will help you understand. You are right about the experiments. In fact time in fact dilation and length contraction must be considered in the engineering of detectors used in high energy particle experiments.
I suppose that i'm seeing it from a different perspective, I know i'm wrong but it's hard at the moment to see otherwise as i've gone down this route of thought.
Whoa now my brain is in meltdown!
You have to throw away your intuition that velocities add linearly - they don't: c + c = c for instance.
The "interval" is what replaces "distance" in spacetime, distance^2 = dx^2 + dy ^2 + dz^2, but interval^2 = dx^2 + dy ^2 + dz^2 - (c dt)^2. Take any two events, calculate the interval according to your frame, and all frames will agree with you (but not on distances or time differences). If the interval^2 is positive then the events cannot be in a causality relation to each other. All points on the path of a photon in vacuum have zero interval between them.
As a PS to my previous post, you might want to check out the muon experiment performed at the peak of Mt. Washington New Hampshire. This experiment is described in many physics texts and articles on special relativity. It is a real, compelling and intuitive example of how relativity affects measurement of time and space. Having taught special relativity to physics students for the past 5 years, I think it will be easier to grasp than the more abstract approach using Lorentz. After you understand the concept and accept the strange but real consequences, then dig into Lorentz and the constancy of spacetime.
They say that exercising the brain is supposed to help prevent dementia, in which case thinking about Einstein should be an excellent idea. When I first got into electronics I started playing around with radio. With light, photons are tiny things. With radio, an 800Mhz photon is something you can hold in your hand (figuratively speaking). Take a piece of wire, resonate it at the right frequency and energy disappears. How odd. The energy appears to be in the form of photons that interfere with each other just like waves on the ocean. And if waves travel on an "ocean", surely electromagnetic waves must travel on an 'ocean' too?
So went the thinking in the 1800s, and the 'ocean' was the aether. And if there was an aether that light/radio travelled through, then as the earth went around the sun, if you measured the speed of light in winter and then in summer, you should get a different result. This led to a truly beautiful experiment http://en.wikipedia.org/wiki/Michelson–Morley_experiment#Length_contraction_and_Lorentz_transformation which I thought I once understood, but now I am not so sure! Speed is distance over time, and when travelling faster time slows down, the length of one of the arms of the experiment contracts and they cancel out and so speed stays the same. 1880 to 1910 is a really interesting period in the history of physics, and unlike the things going on with Higg's bosons, mere mortals might have a chance of understanding the experiments from back then and what they mean.
As Lev says, the muon experiment is very elegant. And we are indeed fortunate to have someone like Lev on the forum who has taught special relativity. Lev probably knows students like Skylight and me - we are the ones at the front with our hands up asking all the difficult questions!
Just to add:
The Michelson-Morley interferometer was exquisitely built and should have easily seen the aether drag if it existed. Which it didn't.
BTW, the earth moves fastest when the earth is closest to the sun, currently a about January 3rd.
And slowest about July 4th.
Duane J
http://www.youtube.com/watch?v=KHjpBjgIMVk
This is covered in Relativity class.
http://en.wikipedia.org/wiki/Length_contraction
As i'm not from a university background I dont see things as easily as some here through mathmatical means I am a person that needs to see practical examples to satisfy my curiousity, from what I have read from comments here is that there are a lot of variables as well as "constants" to take into consideration and with the advent of chaotic theory which physics seems to have evolved to only adds to my belief that nothing can really be taken for granted mathmatically as formulas become more and more dynamic to the point of breaking down.
In the end can we believe our own eyes or is the light hitting them not a reliable measure anymore? (insert not completely convinced smilie here)
With good thought experiments we can at least understand relativity.
Now take the next step into the bizarre world of quantum mechanics.
Objects exist in multiple locations until you look at them which pins down their location.
However, experiments show these things to be true.
QM is not trappable to normal normal experience.
Duane J
I have even heard other scientists saying Einstein got it wrong with some of his theories, when it gets to this situation it's a case of as to who do you believe?
Don't get me wrong I have the utmost respect for the great scientists of past and present, it's just disconcerting when something you held to believe for so long then has doubts cast by others, it's almost like when Newton first turned the physical world and it's theories up to then on their head?
I suppose until we get the theory of everything, their will always be doubts as to "have we got it right so far",
Now I confess that I havn't got the great brain of some but when you hear of those very clever people around today who "may" have wasted decades of their lives following the "wrong" trail (string theory springs to mind) you wonder if you can take it for granted when a theory takes a new route or path because someone has suggested otherwise.
As I suggested before you can see things from a different perspective and even make up your own theories or explanations why you think something isn't quite ringing true, though I have to accept if someone says it is so as they may have seen proof that I havnt been privvy to,
Some individuals like myself need to see that proof in order to be convinced.
In saying that the LHC discoveries, the potential sighting of the "God Particle" is encouraging. Perhaps I was born too early and the next decades or centuries will reveal all?
Newer theories must be consistent with the older theory and all the observations. The newer just moves things forward to explain newer observations.
There was nothing wrong with Newton, it just didn't go far enough. Newton is useful until you get to high speeds.
There was nothing wrong with relativity, it just didn't go far enough. Relativity is useful until you get to the small scale.
There was nothing wrong with Quantum Mechanics, it just didn't go far enough. Quantum Mechanics is useful but doesn't explain the atomic world.
There was nothing wrong with Quantum Electro Dynamics, it just didn't go far enough. QED is useful but there are new observations it can't explain. Although it did predict the recently discovered Higgs Boson.
And now string theory, which is not fully received yet as its predictions are not easily testable.
Each new theory doesn't throw out the old theory, it does expand on the older.
Moreover, the newer theory makes predictions which are then testable. If the predictions don't work out the theory is deemed wrong.
In conclusion, you may hear about some wild theory, but if it is not consistent with all the earlier, (and tested), theories it will be thrown out.
Duane J
So even though I accept most of what is told to us through the media and schooling I have seen stuff that I learnt as a schoolkid been disproved and no longer accepted as the "fashionable theory".
Some of these programmes i've watched that have earned "credibility" as science programmes over the years such as 'Horizon' have even suggested that some more devious physicists have made good livings out of coming out with outrageously complex theories that no-one can prove or disprove.