Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Pmb on 07/08/2013 20:58:11
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Hi folks,
I'm curious about something. So many people here have very different ideas about what they want to get out of physics and areas like special relativity. For reasons of my own I'm considering writing a texbook on special relativity. It'll be for the more advanced undergraduate student. Are there any of you out there? At least fr someone fluent in basic math (algebra, trig, geometry, calculus).
My question is this; what do you want to learn from such a text? There's a great deal of knowledge that can go into an SR book and I can list them if you'd like. I'm more curious about what each of you loves to learn about and what you'd like to get from an SR text.
Thanks.
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Among other things I would like to see this:
http://www.google.it/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CDkQFjAB&url=http%3A%2F%2Fwww.itep.ru%2Ftheor%2Fpersons%2Flab180%2Fokun%2Fem_3.pdf&ei=_HoDUvHPOsaq4ASAu4CgDA&usg=AFQjCNEqtWq6w4BPNt3gZAooAxTdB9KYTw&sig2=Y4dsh70b4jMcgtSdPzm6SQ&bvm=bv.50500085,d.Yms
<<Letter from Albert Einstein to Lincoln Barnett, 19 june 1948. Einstein wrote in German; the letter was typed and sent in English. The highlighted passage in this excerpt says: "It is not good to introduce the concept of mass M = m/sqrt(1 - v2/c2) of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the 'rest mass' m. Instead of introducing M it is better to mention the expression for the momentum and energy of a body in motion."
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lightarrow
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Why? It's not a history book. I was asking what particular SR physics people want to see in an SR text.
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Why? It's not a history book. I was asking what particular SR physics people want to see in an SR text.
That was only an extrat of the Okun's article. That article would be a good introduction for the subject of mass in relativity. Had I read it before, I would have understood that subject much before in my life.
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Another subject I'd like to see is: "Does time flows differently if you travel close to light speed? or if you stay close to a strong gravitational field"
(Of course the answer is no and I'd like to see stated it explicitly and explained in detail why not).
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Another subject I'd like to see is: "Does time flows differently if you travel close to light speed? or if you stay close to a strong gravitational field"
(Of course the answer is no and I'd like to see stated it explicitly and explained in detail why not).
The first part is answered in sections which discuss time dilation. The second is part of GR and not probablky won't be included. Thanks!
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Another subject I'd like to see is: "Does time flows differently if you travel close to light speed? or if you stay close to a strong gravitational field"
(Of course the answer is no and I'd like to see stated it explicitly and explained in detail why not).
The first part is answered in sections which discuss time dilation.
I know, what I intended is that people often makes confusion about it (see also recent threads here) and I'd prefer to see explicitly written, for example (I'm quoting you):
"Please note that time is relative. This means that someone traveling with a moving clock will not observe it to be moving slowly but at a normal rate. Its only when two clocks in relative motion are compared does one appear to be running slow relative to the other."
Another thing I'd like to see is how to solve the "two electron's paradox":
two electrons are moving side by side at the same constant speed along a straight line. In the frame of reference of the electrons they are repelling according to Coulomb's law; in the laboratory frame, they are repelling and also attracting according to Lorenz force because they both create a magnetic field around, so the repulsive force seems it have to be lower.
I know the answer but I haven't find the explicit solution to this problem in any book (it took me a lot of effort and help from others).
Another interesting problem I didn't find the explicit solution is to show that energy and frequency of an EM wavepacket transform in the same way under Lorenz boost.
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lightarrow.
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Thanks. I'm unaware of the electron problem. Can you tell me more about it?
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My question is this; what do you want to learn from such a [SR book] ?. I'm more curious about what each of you loves to learn about and what you'd like to get from an SR text.
I would love to learn what is causing the relativity of space?
What is it that makes the space be relative?
What kind of mechanism shrinks down my ruler (as observed by another inertial observer moving relative to me)?
The relativity of space imply that the reality as a whole is a morphing kind of thing?
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I would love to learn what is causing the relativity of space?
What is it that makes the space be relative?
What kind of mechanism shrinks down my ruler (as observed by another inertial observer moving relative to me)?
The relativity of space imply that the reality as a whole is a morphing kind of thing?
No, the explanation is quite prosaic, it relies on the definition of "lenght", that is of "distance" between two points in space. We usually believe this definition is independent of time, but it's not!
A trivial example: let's imagine you want to measure the lenght of a moving train, measuring the position of the head and the tail's train. But you measure the head's position at the instant of time 00:00:00 and the tail's position, let's say, at the instant of time 00:00:12 (12 seconds later); then you measure with a ruler the distance between these two points and you find it's, let's, say, 1 mm! Of course the train is actually many tens of metres long...
So the measure of the head and tail's position have to be made simultaneously. It's this which "links" irrevocably space and time.
Special relativity teches us that "simultaneity" is frame dependent (if two events are simultaneous in an inertial frame of reference, then they are not in another inertial frame of reference which is moving with respect to the first) so it's for this reason that the *measure* of an object's lenght depends on the object state of motion in the frame of reference where you make that measure.
The objects doesn't actually elastically contracts, its structural properties are exactly the same as before (as long as it moves at constant speed; if it's accelerating it's another story).
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Note: This will be an advanced text. The intended reader will be a physicist who wants a good reference for relativity and an undergraduate text for SR and/or EM in a relativistic fashion. The text will assume the reader knows basic math such as algebra, trigonometry, geometry, calculus and vector analysis.
I would love to learn what is causing the relativity of space?
What is it that makes the space be relative?
Everything I've done so far is online at
http://home.comcast.net/~peter.m.brown/sr/sr.htm
SR is based on the following two postulates:
(1) The laws of physics are the same in all inertial frames of reference.
(2) The speed of light has the same value in all inertial frames of reference.
Using these two postulates one can derive a relationship between space and time measurements in one frame to those in another frame. See
Time dilation- http://home.comcast.net/~peter.m.brown/sr/light_clock.htm
Lorentz Contration - http://home.comcast.net/~peter.m.brown/sr/lorentz_contraction.htm
Lorentz Transformation - http://home.comcast.net/~peter.m.brown/sr/lorentz_trans.htm
Intro to spacetime - http://home.comcast.net/~peter.m.brown/sr/spacetime.htm
What kind of mechanism shrinks down my ruler (as observed by another inertial observer moving relative to me)?
It has to do with the way the ruler is measured. See above derivations and let me know if you have trouble following them.
The relativity of space imply that the reality as a whole is a morphing kind of thing?
No.
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Thanks. I'm unaware of the electron problem. Can you tell me more about it?
In the lab frame, the 2 electrons are both moving at a constant velocity v along the positive x; in their frame they are along y (for example their positions are (0,0) and (0,1) ). Imagine they are connected with a spring, so, because of their coulombian repulsion, their distance is steadily L, this in their frame.
In the lab frame, however, there is also the magnetic force (Lorenz force) which is attractive, so their distance should be less than L.