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All About Light
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Relativistic - Relativistic Confusions

c and Einstein  |  c Top Speed  |  Speed & Speed  |  Faster than c?
Mass Gain  |  E=m*c^2  |  Age Slower  |  Time Dilation  |  Twin Paradox
Dopper Shift  |  Ticketed  |  Simultaneity  |  Competition  |  Fast Strudel
Paradox? No!  |  Confusions  | 
On the previous pages I described some consequences of Einstein's theory of relativity. However, people are often confused about certain aspects of this theory. The purpose of this page is to address some misunderstandings.

Please remember :

  1. Systems that undergo acceleration are not inertial systems. They are not equivalent to each other in the sense of special relativity. They are distinguishable.

  2. Light has a dual character. It is both an EM wave and particles called photons.

  3. Nothing can travel faster than light does in a vacuum.

  4. Massive objects can never reach the speed of light in a vacuum

  5. In media, due to interaction with matter, the speed of light is not the highest possible speed.
  6. It is not possible to travel backward in time.

  7. It is possible to travel forward in time (just wait a little bit).

  8. Einstein's equations were designed to describe objects moving slower than the speed of light in a vacuum. They were derived under the assumption that nothing moves faster than the speed of light in a vacuum. Therefore it is wrong to try to apply them even in HYPOTHETICAL experiments. One cannot say " For a second, let us assume I move with the speed of light in a vacuum." (If you have an interpreter from English to German, and you speak to him in German or English, he will produce something meaningful. However, if you talk to him in Chinese, he will produce either nothing or nonsense.)

  9. Two speeds in relativity do not add according to the simple classical rule w=v+u; therefore 1+1 is never 2 in relativity.

  10. The speed of light is the same in EVERY inertial system, no matter how fast an object is moving.

  11. Simultaneity of events is an observer-dependent notion. Two events that are simultaneous in one frame of reference (call it A) are not simultaneous in an other frame of reference (call it B) if B is moving with a non-zero speed with respect to A.

  12. If you think you designed an experiment disproving Einstein's theory of relativity, you should think again and re-examine your assumptions. Einstein's postulates have been tested rigorously and in many different ways, repeatedly confirming their implications.

 With these few remarks I have finished my discussion of relativistic effects. On the next page, I will touch a little bit on the connection between light and the quantum world.

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last modified 1/5/2001   email Fermilab