RELATIVITY; ILLUSION OR REALITY

[NWOBUMICHAEL]

please everybody i have a question i will like somebody to help me out . can somebody tell me the;

1. Reason why relative motion causes relativity(variation in the physical
quantity e.g time,distance or frequency, as measured by different frames).

2. Quantum theory says we cannot measure two motion properties of an electron at same time. Does that mean that even an electron cannot have knowledge of two of its motion properties at same time?

3. why is light speed an exception to the postulate of speed being relative?

 

[darkmatter4brains]

pls everybody i have a question i will like somebody to help me out . can somebody tell me the;

1. Reason why relative motion causes relativity(variation in the physical
quantity e.g time,distance or frequency, as measured by different frames).

It's not relative motion that causes relativistic effects. We had relative motion before we had Einstein in Galilean and Newtonian physics. Its the constancy of the speed of light that causes relativisitc effects like time dilation, length contraction etc. This is mainly because once the speed of light is considered constant for ALL inertial observers, the relativity of simultaneity is inescapable. Read Chatper 1 of Barnard Schutz's GR text book for a simple, concise and visual explanation of this. But, it's more than just massless particles restricted to moving at c. It's more important to realize that spacetime is so structured that a c even exists such that the metric of space time keeps what is called the interval (a type of relation between time and space) invariant. The fact that it does so makes the relativistic effects an inherent property of the structure of spacetime.

2. Qumtum theory says we cannot measure two motion properties of an electron at same time. Does that mean that even an electron cannot have knowledge of two of its motional properties at same time?

Qm doesn't so much say that. It says ANY two non-commuting observables cannot both be known to unlimited precision. In QM, observables like position and momentum are represented by what are called hermitian operators, which are essentially matrices. If the matrices for the corresponding operators do not commute (i.e. AB ~= BA), there will be an uncertainty relation between them.

They come in many pairs and the uncertainty formula typically looks like this:

delta_a * delta_b >= hbar / 2

delta_x represents the spread in x. So, the more precise you know a, the larger the spread in b, and vice versa. Or the more you know about a, the less you know about b.

One such pair is position and momentum. The other most famous one is between energy and time, but has a somewhat differnt meaning than the one above, since time is not a dynamical variable.


In QM, the state of a particle is represented as an abstract vector in an infinite dimensional space (called Hilbert Space) and contains ALL the information about that state. So, in some vague sense, you can say an electron knows all about itself. (Check out page 122 of R Shankar's Principles of QM for more) But as simple observers we're limited to the uncertainty relation.

 

[MeteorWayne]

Let's recall the purpose of the Science 101 forum.

From the Index page:

"This forum is for those seeking an understanding of basic, generally-recognized scientific concepts, with a desire to discuss them intelligently without aggressively debating them. Teachers and students are welcome! "

And from the introductory post in the forum:

"As you can probably gather from the name of this forum, the purpose of this forum is to encourage discussion of basic, generally-recognized science and scientific concepts. This is not the appropriate forum for discussing fringe theories - please go to The Unexplained for that. If you have a question about science - be it space science, physical/earth science, or biological science (both flora and fauna) - please post it here and no doubt someone will have an answer for you. If you are a science newbie, this is an especially great place to ask your questions. Both teachers and students alike are encouraged to participate.

This forum is intended to be welcoming and open to all... but please be sure to discuss and not aggressively debate the issues. Thanks! "