This is a brief introduction to Special Relativity (SR) and a derivation of its most basic result- Time Dilation. This is primarily for the benefit of the junior members here, and anyone who hasn't been able to understand SR properly, and is also intended as a quick reference in order to clear doubts which occassionallly arise when discussing relativity. However, there are some members who continually challenge relativity. Here's a nice oppurtunity for you guys to challenge the theory at its most fundamental level. (Not that anyone had been stopping you from doing so before, but now you can quote me directly and pose your questions). This certainly is a large post, but I believe it's not a waste of space. If it succeeds in silencing even one anti-relativist, it will be more than making up for what it takes up. These guys claim a real lot of space with their anti-relativity posts.

I will begin from the postulates of Relativity. I won't go into how these postulates were discovered. As you might already know, the Special Theory of Relativity is based on two postulates:

(i) The laws of physics are valid in all inertial frames of reference.
(ii) The speed of light is constant for all observers.

What the first postulate means is this. Suppose you're travelling, in a train say, at a uniform velocity. There is no experiment you can conduct inside the train to determine whether you're moving or not. If you drop a ball from a height, it falls straight down. (This may seem contrary to yor experience with actual trains, but that's beause actual trains don't travel with a perfectly uniform speed. There are slight accelerations, in the form of small jerks, all along the way). So, you can't detect your movement without looking outside the train. When I say looking out, I'm implying any activity involving influences from outside the train, like sounds, or the wind. This is an elementary idea. You already know this.

Now, the second postulate, if you think about it, is a bit wierd. Let's get back to the example of the train. If, inside the train (whose velocity with respect to the ground is v), you throw a ball in the direction of motion of the train , and you observe it's velocity to be "u", an observer standing on the ground would it's velocity to be "u+v", according to classical mechanics. Nothing strange so far. Now, suppose you shine a flashlight in the direction of motion of the train. You'll see that the light ray is travelling at a velocity "c". What would be the speed of the light ray as measured by the observer on the ground? According to classical mechanics, it should be "c+v". But we know that it is not so. The stationary observer would also measure the speed to be "c" itself. This is nothing related to optical illusions. It's not like the light coming from inside the train, or going into the train, is distorted or anything.

So what exactly, is happening? As we shall see shortly, space and time themselves are getting 'distorted', so as to speak. Let me illustrate this point. Let's say you're carrying a clock with you. It's not an ordinary clock. It's a peculiar clock which uses light rays and light detectors instead of springs, gears, and other stuff found inside a usual clock. In this clock, one tick, which is a time interval of "t", corresponds to the time taken by a light ray to travel from one end to the other end.

You are going in the train, and you feel like measuring time. So you keep the clock upright, as shown in Fig. 1. Each time the light ray, originating at the bottom of the clock, hits the topside, you count one tick, which is of the duration "t". An observber on the platform is also watching this. But for him, the clock is not stationary. In the time "t", the clock would have moved forward (to the right, in the figure) a distance "vt' ". This is nothing new. The same law applies when you drop a ball from your hand. You would see the ball move directly down, but the observer outside would see the ball travel diagonally down. In this case, the light ray would travel diagonally up, as in Fig.2, according to him. But there's a small difference here from the case of dropping the ball. In that case, the speed of the ball as measured by the observer would have been more than that which you would have measured. However, we know from postulate (i) that the speed of light is constant for all observers. So the outide observer also sees the light ray travel at the speed of "c". But according to him, the light has to cover more distance, because it is travelling diagonally. So, from his point of view, the light ray would not have comleted it's journey in the usual time interval "t". It would take a time " t' ", which is larger than "t". The reverse applies too. according to you, you and the train are stationary, while the ground and the observer are moving. Hence, you will see his clock running slowly.

http://geocities.com/virusmakermad/img.GIF

So we can see that for someone moving with a uniform velocity, time would run slower. Yes, it does mean that time itself runs slower. It is not because we used this peculiar 'light clock'. What would have happened if we had used an ordinary clock? There are no light rays coming in here, so it should work normally, right? Suppose, along with the light clock, you're also carrying an ordinary clock. According to the outside observer, who is also carrying a light clock and an ordinary clock, your light clock should run slow. After a while, you stop moving (with respect to the ground), and compare clocks. According to the observer, your light clock had been running slowly for the interval of your journey, and hence, should now be behind his clock in time. What about the ordinary clock? If it hadn't run slow during the journey, it would be exactly in phase with the observer's clock now. But that would mean that there would be a time difference between your light clock and your ordinary clock, which in turn means that at some point in your journey, you saw the two clocks keeping different times. What would this mean? That, during your journey, you would have been able to see this strange behaviour of the light clock, and would have been able to determine that you were moving (without looking outside). But that would be a refutation of postulate (i). The only way out is to agree that time itself slows down. Or, its objective equivalent, that all the physical processes (including mechanical, chemical, biological, etc.) in the frame slow down.

Let's take a look at the math involved. It's evident from Fig. 2. The distance travelled by the light ray is AB' = ct', and this is the hypotenuse of a right triangle formed by the sides AA' and A'B'.

Using Pythagoras theorem:
(AB')² = (AA')² + (A'B')²
c²(t')² = v²(t')² + c²t²
(t')²(c² - v²) = c²t²
(t')² = t²/(1 - v²/c²)
t' = t / (1 - v²/c²)½

It is usual in Relativity to use the symbols (Beta) β = v/c, and (Gamma) γ = 1/(1 - β²)½. So we can write:
t' = γt

There's a lot more to be explored in relativity. Length contraction, simultaniety, mass variance, etc. Here are a few good links:
Length Contraction, Muon Experiment, and other issues ( "http://www.sciforums.com/showthread.php?p=833683")
Magic through two Millennia (http://www.upscale.utoronto.ca/PVB/Key/relspec.htm#TOP)
Spacetime Wrinkles (http://archive.ncsa.uiuc.edu/Cyberia/NumRel/NumRelHome.html)
Upscale Homepage (http://www.upscale.utoronto.ca/)
Lorentz Transformations (http://arxiv.org/html/physics/9911067)<Br>
I hope you've been able to follow my explanation. Anyway, the above sites will be able to clear
things up.

-Rosnet

Someone should sticky this post. Its its best explanation of relativity for "dummies" that I have read on this site. Thanks Rosnet!

Nice post, Rosnet. I've added it to the FAQ.

Hey! Awesome!

Sciguy1945, the Rosnet post is a treatise in the 'blind attempting to lead the blind'. He mentioned that something would seem a little 'weird'? Here is how weird it gets. If you are driving 80 km/hr and I driving 60 km/hr in the same direction our relative velocity would be simply 80 - 60 = 20 km/hr relative motion.
If I am driving 60 km/hr in the oppsote direction our relative velocity is determined the same way 80 - (-60) = 80 + 60 = 140 km/hr relative motion.We always subtract the velocities we are comparing but we have to keep track of the directions of the motions.

Now if you are moving at .9c and a light pule passes by you in the same direction, what is the relative speed of photon and frame (you)? It is not c - .9c = .1c parallel motion, nor 1 - (-.9c)= 1.9c. No, in the parllel case you will measure the light passing you as c the speed of light as if your frame you were riding in was at at rest with respect to the motion of the light. The special relativity theory is a theory that denies the concept of motion other wuise how can every measuremnt from every frame moving at any speed always result in the measuremnt of c?

Witout any forces of nature applied the physical mass, the stuff shrinks or contracts in the direction of the motion of the frame and time supposedly dilates, or slows down with increasing sopeed , but stioll no observabvble forces applied.

Even if you were traveling at only .1c your relative motion would still be c, not .9c (parallel) or 1.1c (anti-parallel). Only with light or electro-magnetic radiation does this weird stuff apply, supposedly apply. It is a house of cards, a street three-card-monte scheme, a "lets see how far from reality we can get people to accept as physical truth scheme"?

Two observers moving realtive to each other and each sees the other's clock rate as slower than his own. This is not a contradiction in Special relativity Theory, this is taught as righteous special realtivity theory. Question: Do you believe what the teacher says ,or do you maintain fast to a personal principal of, "prove it to me teacher"?


Special relativity theory is a scam sciguy1945, bogus, la Cagada del Toro.
Geistkiesel

Sciguy1945, the Rosnet post is a treatise in the 'blind attempting to lead the blind'. He mentioned that something would seem a little 'weird'? Here is how weird it gets. If you are driving 80 km/hr and I driving 60 km/hr in the same direction our relative velocity would be simply 80 - 60 = 20 km/hr relative motion.
If I am driving 60 km/hr in the oppsote direction our relative velocity is determined the same way 80 - (-60) = 80 + 60 = 140 km/hr relative motion.We always subtract the velocities we are comparing but we have to keep track of the directions of the motions.



Could you please provide a proof of this?

<P>
<IMG src="http://www.geocities.com/virusmakermad/img.JPG" title="Light Clock" alt="Diagram of light clock"></IMG>

<P>
<Br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;


Just one point. To be a little more complete, one should calculate this "round trip" rather than one way. The answer comes out the same and it helps with the next step of deriving length contraction.

Yes, in every derivation I've seen, the example uses a clock which ticks when light completes the round tick, but I thought it would be more manageable to use a one-way trip, because in the other case, there are half's and quarters coming in, whereas in this case, you can get the same result with slightly less effort. But please tell me how you can bring in length contracton here itself. I usually use another method.

The special relativity theory is a theory that denies the concept of motion other wuise how can every measuremnt from every frame moving at any speed always result in the measuremnt of c?
<P>
What do you mean by the relative velocity? If it is defined simply as the difference in velocities of two frames, then you would be right in saying that the second postulate taken literally leads to a scenario where the concept of motion is denied. This is a simple case where you hve to check your premise before arguing. I see that you posed the same question to JamesR in another post. Neither Einstein, nor JamesR, nor I, have defined relative velocity in the sense that you take it. I'll define it here:
<Br>
The relative velocity of a frame A with respect to another frame B, is defined as the velocity of frame A <B>as measured by an observer in frame B</B>.
<P>
Say, you're looking at two cars doing in the same direction at different velocities. One moving at a velocity of 20 units, and the other at velocity of 40 units. The relative velocity of the second car with respect to the first is <B>not</B> 40-20=20 units. It is the velocity of the second car as the observer in the first car would measure. Suppose he does measures it, and also writes it down on a piece of paper which you can see. The relative velocity is the number which you see on that paper. Now, in classical mechanics, it is the same as 40-20. But in relativty, it's different. This is not in contradicion with observed facts or experiments. And this in no way denies the concept of motion. But what you said about this meaning that the frame was at rest, is close to the truth. Because according to the observer in that frame, <I>he is at rest</I>. After all, that's why it's called the theory of <I>Relativity</I>

<Br>
As you might already know, the Special Theory of Relativity is based on two
postulates:
<Br>
(i)The laws of physics are valid in all inertial frames of reference
<Br>
(ii) The speed of light is constant for all observers.
<Br>




Rosnet,
There is a fundamental flaw in your description above in the diagrams. When the light moves down and strikes the reflecting mirror you have the photons reflected in a zig-zag trajectory. This is in violation of one of the most fundamental postulates governing the motion of light.

Remember, the indendence postulate of light?

This says that the motion of the light is independent of the motion of the source of the light. Here though you show the motion of the train imposing a momentum component in the direction of the motion of the train.
The postulates of light demand that the reflected light return along the opriginal trajectory while the inertial frame moves with respect to the invarinat trajectory.

The only way the laws of physics can be the same to both observers is that the light obey the postulates of the independence of the motion of the light for both observers.

Of course the device could also be a one way distance traveled by the light as it moves up to the ceiling that is also moving which also detects the motion of the frame determined by the offset of the light wrt to the original emission point. The insert in the figure is a schematic of the motion of light for reference use.
http://www.msnusers.com/Savadance4me/Documents/aaabsvelmeter.GIF
Eventually the left side of the train will crash into the light as the train moves out from under the moving light. However, before this happens the emitted light is electronically emitted from the front of the train and the process continues.

Your error is understandable as the Michelson Morely team made the exact same error. In the MM case it was probably due to the experimentors calibrating the reflected light beam such that the beginning interference pattern could be constructed such that the motion would indicate variations from the initial calibrated experimental setup. If memory serves me, Dayton Miller indicated that this what occured in the thousands of MM experiments he conducted, which by the way, was consistent with the MM experiment where both measured an "absolute motion" of approximately 8 km/sec, maximizing diurnally. It is truly amazing how trained scientists today still claim the MM experiment was "null" or from some even, "zero". The measured result was 8 km/sec which was slightly more than 1/4 of the expected motion due to the earth orbit. In any event history and history's echos repeat the error.
Here is an explanation using GPS data describing the lack of measuring the orbital motion of the planet. (http://qem.ee.nthu.edu.tw/f1b.pdf) while accepting the possibility of measuring the rotational motion of the planet, with a 104fold increase in resolution.

Determining motion from within the closed train comparment.
Likewise, your assertion that the the observers cannot determine their intrinsic motion from within the train is incorrect as described by the figure showing the ball lady below.

Another method that you only alluded to but left hanging as it were, was the ball you dropped. The illusion you described is also understandable as this is classic SRT misuse of physical law. Even though you see the ball falling in a straight line wrt what you may perceive as a state of rest, you may use that ball to determine your motion. Simply let the ball fall through a hole cut in the floor of the train. You may see the ground rushing past but you conclude that the ground is rushing past you. Now when the ball strikes the ground there are two possibilities of directions the bounce will take (one actually, but for the sake of discussion we will consider two).

If the ground is rushing past the train at rest the ground will impose a chip shot to the ball in the direction of the rear of the train. If the train is moving the ball will return up the same trajectory it took moving down(less some losses due to friction when striking the ground).

However, by this time you will have concluded that your "observation" that the train was at rest was erroneous [there is no physical way the ground is going to impose a momentum impulse to the ball and everyone in the room knows this to be the physical truth]. Only if the train were actually at rest wrt the embankment, also at rest, would you see the ball use the same trajectory when the bounce occurs. You, the observer, should know ahead of time that the embankment cannot accelerate and contribute any motion to the relative motion of train and embankment, ever. You conclude, therefore, that the actual trajectory of the ball was, as all the observers in the universe external to the train see, the ball is moving through absolute space in a parabolic trajectory.

The train is a shell of illusion, only.

Here is a little sketch emphasizing the concept.

Ask yourself, in consideration of the conservation of momentum considerations, and within the constraints of physical possibility, which way the ball is going to bounce assuming the train is moving in the direction the ball lady is facing.
http://www.msnusers.com/Savadance4me/Documents/amomdect.GIF


Geistkiesel :cool:

<P>
What do you mean by the relative velocity? If it is defined simply as the difference in velocities of two frames, then you would be right in saying that the second postulate taken literally leads to a scenario where the concept of motion is denied. This is a simple case where you hve to check your premise before arguing. I see that you posed the same question to JamesR in another post. Neither Einstein, nor JamesR, nor I, have defined relative velocity in the sense that you take it. I'll define it here:
<Br>
The relative velocity of a frame A with respect to another frame B, is defined as the velocity of frame A <B>as measured by an observer in frame B</B>.
<P>
Say, you're looking at two cars doing in the same direction at different velocities. One moving at a velocity of 20 units, and the other at velocity of 40 units. The relative velocity of the second car with respect to the first is <B>not</B> 40-20=20 units. It is the velocity of the second car as the observer in the first car would measure. Suppose he does measures it, and also writes it down on a piece of paper which you can see. The relative velocity is the number which you see on that paper. Now, in classical mechanics, it is the same as 40-20. But in relativty, it's different. This is not in contradicion with observed facts or experiments. And this in no way denies the concept of motion. But what you said about this meaning that the frame was at rest, is close to the truth. Because according to the observer in that frame, <I>he is at rest</I>. After all, that's why it's called the theory of <I>Relativity</I>

When you say according to the observer in that frame "he is at rest" when he knows perfectly well that he is only making a perceptive evaluation, a mental adjusment, while at the same instant not even considering the fact that he is actually moving, both with respect to the other inertial frame or even in the total absence of the other inertial frame.

Rosnet, I disagree, it is far worse than a contradiction when observable facts are not provided the interested parties because the observers deny the reality that the intrinsic velocities can be measured, or known. It is more than contradictory for the reason that the limitation is assumed as a limitation of what the human can learn and know and use for practical application. A space ship from the Earth Federation of Space Forces that may be engaged in some violent activity, read as war, with an alien force that ESFS voluntarily limits knowledge of the ships motion-profile for pure theoretical reasons ionly could have catastrophic implications orders of magnitude more dangerous and harmful to the people of the planet than a simple defeat in a more or less ordinary conflict of total warfare between enemy human states aligned in warring factions against each other.

We aren't disagreeing over definitions. When I say relative motion of the A and B frame you understand perfectly well what I am saying, as I understand you perfectly well.

However, when you say that "he is at rest", this is not a physically accurate statement, or even under real conditions considered even possible. Assume the observers were launched from earth with the 40 and 20 units uniform motions, though neither observer knew of the launching, or accelerations. For either one of the observers to claim he was at rest,the other moving at 60 units when in fact both inertial frames contribute real measured velocity to the measured relative velocity the "he is at rest" statement is patently false by whatever name it is called. I recognize the dogma that SRT describes in justifying each observer assuming themsleves in a state of rest, but equivaalnce of inertial frame postulates grants the justrification of observers to assert themselves as as moving and even to measure the intrinsic speed of their ship.

Look at the inherent error SRT imposes on the physical measurement of the motions. In most space ship scenarios, fictional as we describe them here or futuristically real, both ships will assert "the other" is moving and themselves at rest is inserting a huge error in vrtually every measurement of velocity attributes of the co-moving ships. It would be more accurate to simply take the average of frame's relative motion when moving anti-parallel than to grant both ships a known maximum error when averaging would lower that error in most cases. Statistically, the measured, averaged motion would introduce a closer understanding of physical truth. The alternative by adopting the SRT blatantly without modification knowingly results in a maximum error resulting from the meaurements of the relative motion. What can be the value of this?

Likewise, to blindly believe, or to disbelieve, that the intrinsic motion cannot be measured, SRT places a mental handicap in the intellectual potential of the scientist involved in space ship measuring processes, by never even looking for the possibilithy that SRT could be an extremely limited and fabricated theory. The belief systems effectively denies those who "believe" in SRT any use of mental faculties, ever, in questioning the accuracy and value of the theory.

From my observation there is more than an analogous pairing of special relativity theorists from religious believers that unquestioningly have adopted the dictatates of their particlular religion. The harm to the scientist is obvious: the search for improvements or enhancements or even possibly discarding the theory all to gether is never even considered hypothetically, all to the detriment of scientific growth for the industry and the scientist.

The religious believer also suffers, as her search for spiritual betterment has been supplanted by the rules and dogmatic regulations of a prefabricated religious dogma and concept ususally manufactured many generations previous, all detrimental to the personal spiritual growth of the believer.
Geistkiesel :cool:

This says that the motion of the light is independent of the motion of the source of the light.

There is no such postulate in relativity. What relativity says is that the speed of light is independent of the speed of the source or observer.

<Font face= "verdana">

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
This is a brief introduction to Special Relativity (SR) and a derivation of its most
basic results. This is primarily for the benefit of the junior members here, and anyone who
hasn't been able to understand SR properly (MacM, for one), and is also intended as a quick
reference in order to clear doubts which occassionallly arise when discussing relativity.
However, there are some members who continually challenge relativity (MacM for one, in this
case too). Here's a nice oppurtunity for you guys to challenge the theory at its most
fundamental level. (Not that anyone had been stopping you from doing so before, but now you
can quote me directly and pose your questions). This certainly is a large post, but I believe
it's not a waste of space. If it succeeds in silencing even one anti-relativist, it will be
more than making up for what it takes up. These guys claim a real lot of space with their
anti-relativity posts.


So much rhetoric. Also your selfserving posts where you assert others lack understanding is just that serlfserving and devoid any physics or support.

Spatial length contraction is not an optical illusion. It is non-existant. That is clear to anyone willing to look for 30 seconds on its origin.

Given a moving clock between points A and B which when at rest is measured as 1 lyr:

AX------------------------------------------------XB distance 1 lyr = 31,536,000 seconds for a photon going v = c according to the clock at rest.

However, for a clock moving at 0.866c relative to points A and B during a trip between them the clocks tick rate is known to be only 50% and would record only 15,768,000 seconds in the same year. At the stated 0.866c velocity the clock would make the trip in 18,207,852.19 seconds according to its clock and would be seen to have taken 36,415,704.39 seconds by a clock at rest to points A and B.

The fact that the moving clock records less time accounts for the same trip distance at the same velocity. Where tr = comparative tick rate.

t*tr = d/v

Distance did not and cannot have changed. To claim otherwise requires that you equate a tick rate of 1.0 to a tick rate of 0.5. That is you must ignore the physically measured and known fact that the moving clock tick rate has slowed.

Your beloved SRT is full of crap. You create these claims by altering known physics and ignoring physical facts when doing comparisons.

Now you can stick your condensending innuendo you know where. Address these physical facts please.

The only valid conclusion from all this is to assume the moving observer would calculate his velocity as being higher than would be calculated by a resting observer.

Put into a simplified context take two cars with clocks. "A" is a standard atomic clock. Calibrate "B" to tick at 50% of A's rate. Now drive 30 miles at 60 Mph.

A records 30 minutes and calculates he was traveling 60 Mph.
B records 15 minutes and calculates he was traveling 120 Mph.

But during the trip both ran side by side with equal absolute velocities and distances traveled.

Precisely the same situation.

I've already answered this somewhere else. and you're actually making a misleading claim when you say that the moving observes measures 'his own' velocity. He will see himself at rest. But that's only a literal mistake. Okay. Just pointing it out. So you mean that the moving observer would measure the velocity of his surroundings as higher than the velocity that the surroundings would observe as his. You've said this in the other post too. Where do you come up with these ideas? Well, here's another question. There's a car which is moving at 60Mph with respect to the ground. The driver looks at the speed-o-meter (which uses the rate at which the wheel spins when in contact with the road), and, according to you, he should see some number higher than 60, right? tell me how you account for this mechanically. Remember that according to the <I>driver</I>, his own frame is not time dilated. Or are you claiming this too?

I've already answered this somewhere else. and you're actually making a misleading claim when you say that the moving observes measures 'his own' velocity.

Please show where I said any such thing. I believe I said "Calculate".

He will see himself at rest. But that's only a literal mistake. Okay. Just pointing it out. So you mean that the moving observer would measure the velocity of his surroundings as higher than the velocity that the surroundings would observe as his. You've said this in the other post too. Where do you come up with these ideas? Well, here's another question. There's a car which is moving at 60Mph with respect to the ground. The driver looks at the speed-o-meter (which uses the rate at which the wheel spins when in contact with the road), and, according to you, he should see some number higher than 60, right? tell me how you account for this mechanically. Remember that according to the <I>driver</I>, his own frame is not time dilated. Or are you claiming this too?

I am claiming that velocity is a calculated result of a measured distance as marked by a trip time piece. I am making the point that time pieces running at different tick rates accounts for the accumulated time differances and not some spatial change of distance.

Okay, I agree you made no literal mistake. You still haven't answered the speedometer question.

Okay, I agree you made no literal mistake. You still haven't answered the speedometer question.

Thank you.

Now, I see no problem. He would conclude either his speedometer was in error or his clock was wrong or that the other one (car data) was wrong; since he would know he ran side by side with the other car.

If he had the correct mechanical means of determining the number of wheel revolutions (tire circumferance) vs distance he would conclude his clock ticked slow.

I'm not referring to your question. There's only one car here. And there's the ground, and the speedometer, and the driver's clock, and the ground's clock.

I'm not referring to your question. There's only one car here. And there's the ground, and the speedometer, and the driver's clock, and the ground's clock.

Ok. I see you would like to duplicate the error of SRT by limiting ones ability to assess the actual physics.

Well, you fail since, I happen to know the distance I traveled (which I assume you agree matches my odometer), I therefore have to assume my speedometer was off or my clock was off. I most certainly would not assume the distance between points A and B changed. Since my odometer read correctly I would most likely suspect my batteries were weak in my watch. :D

Ok. I see you would like to duplicate the error of SRT by limiting ones ability to assess the actual physics.

Well, you fail since, I happen to know the distance I traveled (which I assume you agree matches my odometer), I therefore have to assume my speedometer was off or my clock was off. I most certainly would not assume the distance between points A and B changed. Since my odometer read correctly I would most likely suspect my batteries were weak in my watch. :D This is the aspect of special relativity that I've always thought stinked of something fowl. I've never liked the concept of length contraction even though I know why it is required by special relativity and the such.

Ok. I see you would like to duplicate the error of SRT by limiting ones ability to assess the actual physics.

Well, you fail since, I happen to know the distance I traveled (which I assume you agree matches my odometer), I therefore have to assume my speedometer was off or my clock was off. I most certainly would not assume the distance between points A and B changed. Since my odometer read correctly I would most likely suspect my batteries were weak in my watch. :D

How can you see your own clock dilate. If everything in your frame, including you, slowed down, then you wouldn't feel that anything has slowed down at all.

Ok guys, this thread was intended for the use of people whom, like myself, lack a thorough background into the theory of relativity. The information compiled by Rosnet will continue to be greatly useful to anyone looking to get into this type of physics.

Rosnet never claimed that this was the be all and end all of relativity.

If you all don't mind, please your "discussions" for threads that are meant for them. All it does is Overwhelm new people. ;)

Thanks

I think you didn't read the first paragraph recently. I''ve edited my post, and amade a few changes. And I think it's a good idea for a learner to look at the arguments going on. firstly, you should really hear both sides before making up your mind, and secondly there may be questions which you haven't asked, but are critical to a good understanding of the theory. And try to solve the problems posted here by MacM and others. That'll make your understanding thorough. However, you do have to understand length contraction before doing so. I plan to make a post relevent to this soon.

Its your thread I suppose...You know that a lot of "crack" ideas will get thrown around; witht the best intentions of course. Hopefully all the newbies will be able to sieve through them.

Sure. You should be prepared to spend time and thought on it if you want to learn it properly. But you're right. It'll be quite difficult. Relativity is confusing enough without having to go through 'crack' ideas.

Its your thread I suppose...You know that a lot of "crack" ideas will get thrown around; witht the best intentions of course. Hopefully all the newbies will be able to sieve through them. Just don't read any posts by MacM. His explainations are completely contrary to the theory of special relativity. (or if you do want to read them, just keep that in mind)

MacM's threads are usually directed towards one person only and I aviod them usually. ;)

How can you see your own clock dilate. If everything in your frame, including you, slowed down, then you wouldn't feel that anything has slowed down at all.

Funny, show me where I have ever said one measures or sense his own inertial motion or sees his clock dilated? I never have. But that is no bases to ignore the accumulated emperical physics which you also support (as well as I do) that a clock in motion becomes dilated.

To ignore that calculated change in tick rate is the only basis to claim a physical spatial distance contraction. What I have said is distance does not contract and the relavisticly moving observer therefore msut either calculated he attained a different velocity for the trip or assume his clock slowed down.

Because to claim both length contraction of space and time dilation as physically real consequences causes an observer moivng at 0.866c to make the trip in 25% of the time, not the standard 50% of the time.

Where tr = tick rate @ 0.866c tr = 0.5 vs th standard at rest clock.

The standard formula t = d/v must be changed to include the accepted physical fact of time dilation due to motion before computing any relavistic gendankin such that:

t * tr = d / v and it can be seen that by retaining the accept fact of time dilation on the moving clock that the trip will take t = d / (v * tr).

Where d = 1, v = 1

t = 1 / (1 * 0.5) = 0.5 and there is simply no physical room for a distance contraction.

Stop ignoring time dilation when you want to claim spatial contraction. You unwittingly equate a tick rate of 0.5 to a tick rate of 1.0 and you are mixing frames to assert length contraction.

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Now, the second postulate, if you think about it, is a bit wierd. Let's get back to the
example of the train. If, inside the train (whose velocity with respect to the ground is v),
you throw a ball in the direction of motion of the train , and you observe it's velocity to
be "u", an observer standing on the ground would it's velocity to be "u+v", according to
classical mechanics. Nothing strange so far. Now, suppose you shine a flashlight in the
direction of motion of the train. You'll see that the light ray is travelling at a
velocity "c". What would be the speed of the light ray as measured by the observer on the
ground? According to classical mechanics, it should be "c+v".
I disagree. The speed of light is constant measured by all observers, but the relative velocity of frame and photon is as stated.

Suppose we have a length to a mirror measured on the train determined wrt the stationary train. When we shine a light at that mirror and time its return time we see a discrepancy with the stationary case.
When the light is emitted it will arrive at a distance ct (assumed to be the position of where the mirror was placed). However the light has moved a distance vt in the time the light has moved ct. To reach the mirror from herethe light must travel another vt plus the distance the train moves in the meantime, vt' say this distance is ct'= vt + vt', or t' = vt/(c - v). This is sufficent itself to determine the train is moving. If the train were not moving t' would be zero. This is the classical way the light would be measured, not as Rosnet assumes.

Rosnet makes the mistake of moving the frame from where the speed of light is constant wrt the vacua inside the train abn tries to have us believe he has operformed some rational exeperimental activity.

The stationary observer would also measure the speed to be "c" itself. <B>This is nothing related
to optical illusions</B>. It's not like the light coming from inside the train, or going into the
train, is distorted or anything.
<Br>

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Rosnet makes the same mistake Einsgtein made when he changes the refernce frame from the vacua out side the train, to inside the traain and then equates the conditions. He also mistates what a classical,Newtionain measurement would result in.[/indent]
Rosnet,
In Einstein Book "Relativity" he makes the claim that the speed of light in vacua is constant. He devlops the same model used by Rosnet and has the air removed from the stationary frame and it is in this frame that the speed of light is measured as a universal constant. Then Eintein places the light inside the train and equates this light motion to the man walking on the train, or of Rosnet throwing the ball.

But as the measured speed of light comes out as c - w, which is less than the speed of light, this value of measurement is discarded.

Do you see the fallacy of Rosnets argument and his unconscious but robotic switchuing of frames of reference. your The argument regarding the speed of light was wrt the vacua, outside the train, not inside. Einstein, like Rosnet, switched frames of reference making the conclusion a non-cnclusion, as in Rosnet's argument also.

It isn't so much that Rosnet doesn't understand physics, he doesn't even understand relativity theory.

Geistkiese :cool:

Sorry, but I didn't understand the mirror experiment. Can you explain it again, stating which observer is in which frame, and who is moving with respect to whom?

“ Originally Posted by Rosnet



Now, the second postulate, if you think about it, is a bit wierd. Let's get back to the
example of the train. If, inside the train (whose velocity with respect to the ground is v),
you throw a ball in the direction of motion of the train , and you observe it's velocity to
be "u", an observer standing on the ground would it's velocity to be "u+v", according to
classical mechanics. Nothing strange so far. Now, suppose you shine a flashlight in the
direction of motion of the train. You'll see that the light ray is travelling at a
velocity "c". What would be the speed of the light ray as measured by the observer on the
ground? According to classical mechanics, it should be "c+v".

Rosnet,

No this is incorrect, you are in error here.
De Sitter, even as recognized by AE ("Relatvity", 1916, Ch. VII) , that the speed of light is independent of the speed of the source of the light. Unlike the ball thrown on the train where the speed of the train is set to rest wrt the ball (arriving at the speed of gthe ball wrt the train), in the case of light the speed of the train must be "subtracted",to insure the independence of the light source speed and lightspeed, and not assumed at rest. To treat the ball and light the same you impose a dependence of the speed of light and the speed of the source of light, your mistake here.

Therefore, AE erred grossly by imposing an erroneous "classical" interpreation on the light train scenario and all of this in the same chapter 7 of "Relativity".

Geistkiesel :cool:

Sorry, but I didn't understand the mirror experiment. Can you explain it again, stating which observer is in which frame, and who is moving with respect to whom?


Rosnet,
Yes, see below. This is about as clear as it gets. If you have any questions I will answer them.
http://www.msnusers.com/Savadance4me/Documents/step1.GIF

Geistkiesel :cool:

MacM,

Take a look at the figure I posted for Rosnet above. You've seen it before in other threads I am sure. Anyway, when the left photon arrives at the left clock, the right photon is still a distance away from the right clock.

Here is a "clincher".

For a brief instant both lights are moving in the same direction: the left reflects while the right continues untill arriving at the right clock. This is to my way of seeing, "time dilation", which doesn't actually affect clock rates; it puts a devilishly and cleverly hidden addition to clock times that are timing events giving a false impression of time dilation.

Geistkiesel :cool:

Sorry, Geistkielsel, I don't get to see any images that you post. I even got an msnusers account, but it didn't help.

Rosnet,
Yes, see below. This is about as clear as it gets. If you have any questions I will answer them.

***Geistkiesel's Clear Section***


http://www.msnusers.com/Savadance4me/Documents/step1.GIF


***************************
Geistkiesel :cool:
Yes Geist - that is about as clear as it gets with you.

Can someone who can vies the picture please save it and attach it from somewhere else?

Can someone who can vies the picture please save it and attach it from somewhere else?

No one can view the picture, it appears to have a temporary internet address. That is, Geist uploaded it to MSN and hotlinked the preview picture of his upload.

MacM,

Take a look at the figure I posted for Rosnet above. You've seen it before in other threads I am sure. Anyway, when the left photon arrives at the left clock, the right photon is still a distance away from the right clock.

Here is a "clincher".

For a brief instant both lights are moving in the same direction: the left reflects while the right continues untill arriving at the right clock. This is to my way of seeing, "time dilation", which doesn't actually affect clock rates; it puts a devilishly and cleverly hidden addition to clock times that are timing events giving a false impression of time dilation.

Geistkiesel :cool:

Sorry, I too am unable to view your posted graphics.

Sorry, I too am unable to view your posted graphics.

MacM, Rosnet, Funkstar et al. I was unaware that you could not view the figure. I can see it so I assmed everyone else did also. Here is another try. As I mentioned there is a brief moment when the lights are moving the same direction which is when the left moving light reflects from the left mirror/clock and the right photon is still moving toward the right mirror/clock. To me this is the mysterious added time (some might call it "time dilation")for the round trip of the light when compared to the test in the embankment frame. The additional time only occurs when the frame is in motion wrt the embankment.
http://www.msnusers.com/Savadance4me/Documents/step1.GIF

In any event it seems impossible for the lights to arrive at the L and R clock/mirrors simultaneously when the frame is moving. Too much to happen i.e. time dilation and/or frame contraction on the two halves of the frame and violates every symmetry consideration in the book.

So before you trash it, if that is your intent, give me an opportunity to explain it. It is counter intuitive to the SR trained so it might seem strange to some.

Geistkiesel :cool:

[indent]MacM, Rosnet, Funkstar et al. I was unaware that you could not view the figure.

Sorry Geist.., I still get a square with a red 'X'.

Geist, why don't you take a geocities account or something?

Geist, why don't you take a geocities account or something?
Why don't you at least pretend to be a scientist?

Geistkiesel

I don't understand the relevance of your post. Iwas refering to the fact that we are not able to view the pictures you've posted, apparently because they are from some msnusers link. I was suggesting that you get a geocities (yahoo) account, and post them from there.
Did you think I was insulting you in some manner?

Why don't you at least pretend to be a scientist?

Geistkiesel
Excuse the rude reply. I was on edge and assuming the world as an enemy. Upon reflection I see your post was well meaning and my response was totally unjustified.

Geistkkiesel :cool:

No harm done.

wat a dumb thread

If the light source is emitting photons vertically uowards, at discreet intervals while it is travelling on the train, then it seems that this photon trajectory woould appear to have a "down and to the right" slant to the observer. I assume that geistkiesel is correct and the train cannot impart momentum to the photons, which means that the photons are travelling strictly vertically upward. It is the light source which is moving and giving the illusion of horizontal motion of the photons. So how can this trajectory contain considerations and calculations that light itself is going that fast. To geistkiesel: If the ball were dropped through the hole while the train were travelling relative to the ground it would bounce up through the hole. If the train were still and the ground were moving the ball would behave the same and come up through the hole. This example like the others excludes the effect of friction which does not enter into relativistic considerations.

I have written just one reply and was told that it was a repeat of something i submitted. that was my first submission in 4 weeks. thank you steponit

relativistic experts go read my topic about infinite speed of light please! :)

<!-- An introduction to Special Relativity and Time Dilation -->
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;This is a brief introduction to Special Relativity (SR) and a derivation of its most basic result- Time Dilation. This is primarily for the benefit of the junior members here, and anyone who hasn't been able to understand SR properly, and is also intended as a quick reference in order to clear doubts which occassionallly arise when discussing relativity. However, there are some members who continually challenge relativity. Here's a nice oppurtunity for you guys to challenge the theory at its most fundamental level.

Now, the second postulate, if you think about it, is a bit wierd.



I for one appreciate being able to occassionallly have a nice oppurtunity to challenge a wierd postulate.

It's a refreshing break from occaisionally having an opportunity to challenge a weird postulate.