Doubts in special theory of relativity

[ash64449]

I know this wasn't your main point and I'm not sure exactly what you are saying here, but (at least for the sake of others that might read this for info) it should be emphasized that Maxwell's theory does contradict Galilean Relativity and when we compare our motion with light, we cannot discern whether or not we are moving. Uniform motion can only be defined after choosing a reference which may be chosen arbitrarily. I found this paragraph a little confusing; perhaps I misunderstood what you meant.

I mean when we use old mechanics theorem of addition of velocities,Light speed would decrease to the observer who is actually moving.but he will think he is in rest.So if he measure light speed(i mean according to theorem of addition of velocities),He will measure slower speed.So can't he use this to understand whether he is moving or not? That is why Theorem of addition of velocities of old mechanics violate Principle of relativity as well as Galileo's theory of relativity. Understood?

 

[ash64449]

That's certainly better than nothing, but I don't know why everyone chooses to study the original papers instead of modern presentations. A presentation based on spacetime diagrams is far easier in my opinion, and they hadn't even been invented in 1905.

My favorite intro to SR is the one in the first few chapters in the GR book by Schutz. Link. The one by Taylor & Wheeler is the one that gets the most recommendations, so it's probably very good too. It's also recommended by Schutz, in the following words:

There are many good introductions to SR, but a avery readable one which has guided our own treatment and is far more detailed is Taylor & Wheeler (1966).​

Ok. Friend. Thank you for your advice. I didn't find any difference in Einstein's 1905 paper and my relativity book. They both explain time beats at different rate based on simultaneous consideration.Let me look for other option.

 

[ghwellsjr]

My favorite intro to SR is the one in the first few chapters in the GR book by Schutz. Link. The one by Taylor & Wheeler is the one that gets the most recommendations, so it's probably very good too. It's also recommended by Schutz, in the following words:

There are many good introductions to SR, but a avery readable one which has guided our own treatment and is far more detailed is Taylor & Wheeler (1966).​

The first edition of Taylor and Wheeler (1966) is a good book. Unfortunately, most people buy the second edition (1992) which is very much different and has caused much confusion on this forum. Don't assume that Schutz's recommendation of the 1966 edition applies to the 1992 edition.

 

[ash64449]

The first edition of Taylor and Wheeler (1966) is a good book. Unfortunately, most people buy the second edition (1992) which is very much different and has caused much confusion on this forum. Don't assume that Schutz's recommendation of the 1966 edition applies to the 1992 edition.

Oh no! I took the second edition! Can i get first edition? where?

 

[Fredrik]

The first edition of Taylor and Wheeler (1966) is a good book. Unfortunately, most people buy the second edition (1992) which is very much different and has caused much confusion on this forum. Don't assume that Schutz's recommendation of the 1966 edition applies to the 1992 edition.

You have made me curious. I wasn't aware of this, since I haven't read either edition. If it has been discussed here, I must have missed those posts too. In what way is the second edition worse?

 

[ghwellsjr]

Oh no! I took the second edition! Can i get first edition? where?

Maybe from a library.

 

[ghwellsjr]

You have made me curious. I wasn't aware of this, since I haven't read either edition. If it has been discussed here, I must have missed those posts too. In what way is the second edition worse?

Here is the main issue. The emphasis of the book is their unique definition of the term "Proper Clock" which is what everybody else means by an inertial clock that measures a time-like spacetime interval and how they apply it to just about every problem and scenario.

Here is a case where the confusion came up. Scroll down to post #39 and following.

 

[ash64449]

Here is the main issue. The emphasis of the book is their unique definition of the term "Proper Clock" which is what everybody else means by an inertial clock that measures a time-like spacetime interval and how they apply it to just about every problem and scenario.

Here is a case where the confusion came up. Scroll down to post #39 and following.

Yes.i encountered this problem too. So how can we resolve from this paradox?

 

[ash64449]

Maybe from a library.

Which library?

 

[ghwellsjr]

Yes.i encountered this problem too. So how can we resolve from this paradox?

What problem? What paradox?

I was talking about a unique terminology issue and the insistence that a particular way of solving SR problems is superior.

 

[ash64449]

What problem? What paradox?

I was talking about a unique terminology issue and the insistence that a particular way of solving SR problems is superior.

Twin paradox

 

[ghwellsjr]

Which library?

If you can't find it in your local public library, try a university library. They may not let you check it out but they probably will allow you to examine the book in the library.

 

[ash64449]

What problem? What paradox?

I was talking about a unique terminology issue and the insistence that a particular way of solving SR problems is superior.

U said to look at #39.That poster dealt with twin paradox. How can we resolve from this?

 

[ash64449]

If you can't find it in your local public library, try a university library. They may not let you check it out but they probably will allow you to examine the book in the library.

let me try first to get it from internet,then i will try.

 

[ghwellsjr]

Twin paradox

Did you read my summary of T&W's answer:

So their ideal explanation of the Twin Paradox is for the stay-at-home twin to have a Proper Clock and for the traveling twin to carry another Proper Clock, a wristwatch, with him on his trip out, and another, or the same, wristwatch on the trip back, an compare times on them. That, to me, is a ridiculous explanation because the twins already had such clocks.

 

[ash64449]

Did you read my summary of T&W's answer:

OK. I mean what is the answer. How got younger? We cannot use reference frame when we compare two twins.

 

[ash64449]

Did you read my summary of T&W's answer:

in which thread did you wrote that comment? Can i look at it?

 

[ghwellsjr]

in which thread did you wrote that comment? Can i look at it?

Just click on the little icon to the right of my name in the quote.

 

[ghwellsjr]

OK. I mean what is the answer. How got younger? We cannot use reference frame when we compare two twins.

T&W don't like to use reference frames although they admit that there is nothing wrong with doing that. Instead, they point out that any observer in any reference frame can calculate the spacetime interval on an inertial Proper Clock and they will all get the same answer. So we just do this three times, once for the earth-bound twin, once for the traveling twin on his way out and again on his way back and we add the two for the traveling twin and compare it to the earth-bound twin's Proper Clock.

 

[ash64449]

Just click on the little icon to the right of my name in the quote.

please explain me the solution of twin paradox ghwellsjr.. i haven't understood your comment in that thread. You only said their method is wrong. I didn't see anything else.So please explain it to me.

 

[ash64449]

T&W don't like to use reference frames although they admit that there is nothing wrong with doing that.

Why?

Instead, they point out that any observer in any reference frame can calculate the spacetime interval on an inertial Proper Clock and they will all get the same answer. So we just do this three times, once for the earth-bound twin, once for the traveling twin on his way out and again on his way back and we add the two for the traveling twin and compare it to the earth-bound twin's Proper Clock.

You haven't said the solution. You have just said the method. So who will be younger?

 

[ghwellsjr]

please explain me the solution of twin paradox ghwellsjr.. i haven't understood your comment in that thread. You only said their method is wrong. I didn't see anything else.So please explain it to me.

I didn't say it was wrong, I said it was ridiculous.

Here is a portion of a thread where I explain the Twin Paradox. You might want to look on earlier pages too. The good stuff is around post #125.

 

[ash64449]

I didn't say it was wrong, I said it was ridiculous.

Here is a portion of a thread where I explain the Twin Paradox. You might want to look on earlier pages too. The good stuff is around post #125.

How can we explain Time dilation through Doppler effect?

 

[ash64449]

I didn't say it was wrong, I said it was ridiculous.

Here is a portion of a thread where I explain the Twin Paradox. You might want to look on earlier pages too. The good stuff is around post #125.

I have a problem.. I cannot understand space-time diagrams.

 

[ghwellsjr]

I have a problem.. I cannot understand space-time diagrams.

Have you ever been on a treadmill? If not, go to your local fitness center and ask for a demo. It will show you a graph of your "distance" as a function of time, the faster you walk, the steeper the plot. In the page that I pointed you to, my spacetime diagrams are shown very much like what you would see on a treadmill except that in some cases, the distance is negative (like walking backwards on the treadmill). The more common way to show a spacetime diagram is to rotate it 90 degrees so that time goes up and distance goes to the right (or the left for negative distances). The other thing you have to know is that we show light signals traveling along 45-degree lines. Isn't that simple enough?

 

[Fredrik]

I have a problem.. I cannot understand space-time diagrams.

The idea is extremely simple. The diagram shows the assignments of coordinates made by an inertial coordinate system. Each point represents the coordinates of an event. A curve in the diagram represents the motion of a point particle (or something that for our present purposes can be thought of as being point-like). If the curve is a straight line, the particle has a constant velocity. If it's a vertical straight line, the velocity is zero. The more it deviates from being vertical, the bigger the speed. The units on the axes are chosen so that a straight line drawn at 45 degrees represents motion at the speed of light. A curved line represents the motion of an accelerating particle.

The only thing that's a bit tricky is how to figure out how to draw the simultaneity lines of an observer whose motion is drawn in the diagram. A simultaneity line is a set of points that the observer's comoving inertial coordinate system assigns the same time coordinate. How to do this is explained in all the books that mention spacetime diagrams. Once you understand this, you will find it easy to understand all of the standard problems in SR.

 

[ghwellsjr]

How can we explain Time dilation through Doppler effect?

Yes, I do that at the beginning of the thread I just linked you to. Also, try this thread, down around post #7.

 

[Dale]

By this he means that If the clocks satisfy this simultaneous considerations,then these clocks go at the same rate.(my words)

Nowhere in any of the quoted material did he ever use the word "rate". You are making an incorrect inference from what he said to something entirely different.

One problem is that natural language is inherently imprecise, and translations between natural languages are even more imprecise. To precisely discuss these concepts it is important to use math. Mathematically, it is easy to come up with transformations which have time dilation but not relativity of simultaneity and vice versa. What that shows is that you cannot derive one from the other.

 

[ash64449]

Nowhere in any of the quoted material did he ever use the word "rate". You are making an incorrect inference from what he said to something entirely different.

One problem is that natural language is inherently imprecise, and translations between natural languages are even more imprecise. To precisely discuss these concepts it is important to use math. Mathematically, it is easy to come up with transformations which have time dilation but not relativity of simultaneity and vice versa. What that shows is that you cannot derive one from the other.

please read the pdf book that i earliar said. It explained relativity of simultaneity to explain that time go at different rates. Please look at it. And you see by reading that book that i am making incorrect conclusion,please tell me what i was wrongly understood by reading that book.

 

[ash64449]

Nowhere in any of the quoted material did he ever use the word "rate". You are making an incorrect inference from what he said to something entirely different.

One problem is that natural language is inherently imprecise, and translations between natural languages are even more imprecise. To precisely discuss these concepts it is important to use math. Mathematically, it is easy to come up with transformations which have time dilation but not relativity of simultaneity and vice versa. What that shows is that you cannot derive one from the other.

but i am not good in math. Please explain it to me in other ways other than math. To understand relativity,higher algebra is required. I haven't reach that class yet. But i do really want to understand relativity now..

 

[Fredrik]

but i am not good in math. Please explain it to me in other ways other than math. To understand relativity,higher algebra is required. I haven't reach that class yet. But i do really want to understand relativity now..

Actually, the algebra is very simple. But there's an even easier alternative, and that is to use spacetime diagrams. So you should start working on understanding them right now.

Note that SR is unique in physics in that it's possible to understand the essentials by talking about pictures that involve nothing but straight lines. There's no other theory that can be even partially understood without a significant amount of math.

 

[ghwellsjr]

By this he means that If the clocks satisfy this simultaneous considerations,then these clocks go at the same rate.(my words

Nowhere in any of the quoted material did he ever use the word "rate". You are making an incorrect inference from what he said to something entirely different.

Yes he did. Right in the middle of section 4 of his 1905 paper, he said:

What is the rate of this clock, when viewed from the stationary system?

Ash64449 later stated:

note this chapter explain why two clocks are not synchronous.i.e it shows clocks on stationary observer and clocks of moving observer relative to stationary system do not go at the same rate.

He may be coming to the correct conclusion for the wrong reason but it sounds like he has learned that a moving clock ticks at a different (slower) rate in a particular frame than a stationary one (or than the Coordinate Time of the frame) but what I think he is having trouble with is that in the rest frame of that moving clock, the previously stationary clock is now ticking at a slower rate than the previously moving clock (or than the Coordinate Time of the previously moving clock's rest frame).

I thought ash finally understood this point in post #32 from what you said in post #30 but apparently not.

 

[Dale]

please read the pdf book that i earliar said. It explained relativity of simultaneity to explain that time go at different rates. Please look at it. And you see by reading that book that i am making incorrect conclusion,please tell me what i was wrongly understood by reading that book.

I have read that book multiple times as well as the 1905 paper. They simply do not support your claims.

You claim that relativity of simultaneity (different frames disagree on which events are simultaneous) implies time dilation (moving clocks run slow). That is simply not correct. The texts you refer to never make that claim, and in fact do not even discuss the rate of clocks in the sections you mention.

Here is a post where I provided a mathematical counterexample to a similar claim made by another poster. This transform proves that relativity of simultaneity does NOT imply time dilation: https://www.physicsforums.com/showpost.php?p=3751522&postcount=2

 

[ash64449]

Yes he did. Right in the middle of section 4 of his 1905 paper, he said:


Ash64449 later stated:

He may be coming to the correct conclusion for the wrong reason but it sounds like he has learned that a moving clock ticks at a different (slower) rate in a particular frame than a stationary one (or than the Coordinate Time of the frame) but what I think he is having trouble with is that in the rest frame of that moving clock, the previously stationary clock is now ticking at a slower rate than the previously moving clock (or than the Coordinate Time of the previously moving clock's rest frame).

I thought ash finally understood this point in post #32 from what you said in post #30 but apparently not.

yes. You are right.i understood.thank you!

 

[ghwellsjr]

Still i am curious you see. What i mean is that time beat slower to the one who is moving relative to someone who is not.(just an example) Events that take place to that someone who is not moving takes place to the one who is moving relative to someone.(no additional events takes place) Since time dilates to that observer who is moving,What will happen to the events according to him when compared to the one who is not moving?

Events are assigned coordinates according to an arbitrarily chosen Inertial Reference Frame (IRF). You use the Lorentz Transformation process to re-assign coordinates to a second IRF moving with respect to the original one. You should think in terms of IRF's--not observers. When we say an observer's frame or according to an observer, we simply mean an IRF in which the observer is at rest. But all observers, clocks and other objects are in all IRF's as well as all events. If you do this it this way, Time Dilation happens automatically, as well as all the other aspects of SR.