I Relativity's "time dilation" or clock accuracy alteration

[Crowxe]

i've seen the double slit experiment and the delayed choice . my mind rejected the conclusion, but the experiment setting and configuration of delayed choice is rational and holds water so i accepted the experiment outcome even if it means the world isn't real.

i had to give that intro that sounds irrelevant to the topic just to show that I'm open minded.

Now, for the relativity and time dilation , my argument starts with the light clock, it's designed and calibrated to "count" time in certain conditions same as those large old classic pendulum clocks that are calibrated in certain conditions and they measure time faster in winter as the pendulum rod shrinks or slower during high atmospheric pressure and humidity but we don't age faster in winter nor slower in humid thick air, so why should we say so if a clock that uses different theory gave altered reading??

 

[PeterDonis]

it's designed and calibrated to "count" time in certain conditions

Technically, yes, but they're much more consistent and repeatable conditions than you get with a pendulum clock. Basically you need light bouncing between two mirrors in a vacuum. Under those conditions there is no variability at all in a light clock.

We don't actually use light clocks as our best standard of time, we use atomic clocks, but they are similarly calibrated and controlled to minimize variability.

we don't age faster in winter nor slower in humid thick air, so why should we say so if a clock that uses different theory gave altered reading

I'm not sure I understand the issue. Relativity does not predict that we age faster in winter or slower in humid thick air. It predicts that we age according to the rate of an ideal clock (a light clock or an atomic clock is a close enough approximation to this ideal for all practical purposes) that follows the same path through spacetime.

 

[Crowxe]

Technically, yes, but they're much more consistent and repeatable conditions than you get with a pendulum clock. Basically you need light bouncing between two mirrors in a vacuum. Under those conditions there is no variability at all in a light clock.

We don't actually use light clocks as our best standard of time, we use atomic clocks, but they are similarly calibrated and controlled to minimize variability.
I'm not sure I understand the issue. Relativity does not predict that we age faster in winter or slower in humid thick air. It predicts that we age according to the rate of an ideal clock (a light clock or an atomic clock is a close enough approximation to this ideal for all practical purposes) that follows the same path through spacetime.

i agree, "we age according to the rate of an ideal clock" but when those clocks are moving faster, they are not ideal or accurate thus they give wrong reading , so it's not us that age in different rate

 

[Nugatory]

i agree, "we age according to the rate of an ideal clock" but when those clocks are moving faster, they are not ideal or accurate thus they give wrong reading , so it's not us that age in different rate

It sounds as if you are thinking that relativity says that "a moving clock runs slow". That' not right, and that's not what relativistic time dilation says.

We age at a rate that is in agreement with the rate of an ideal clock that is at rest relative to us, which is another way of saying "following the same path through spacetime as we are". The fact that we and the clock may be moving relative to something or somebody else is irrelevant: right now you are moving at 99.999% of the speed of light relative to someone somewhere in the universe, but that doesn't mean that a clock sitting on the table next to you is any less ideal.

 

[Crowxe]

It sounds as if you are thinking that relativity says that "a moving clock runs slow". That' not right, and that's not what relativistic time dilation says.

We age at a rate that is in agreement with the rate of an ideal clock that is at rest relative to us, which is another way of saying "following the same path through spacetime as we are". The fact that we and the clock may be moving relative to something or somebody else is irrelevant: right now you are moving at 99.999% of the speed of light relative to someone somewhere in the universe, but that doesn't mean that a clock sitting on the table next to you is any less ideal.

what I'm saying is that speed (relative or actual) only affect the clock reading. the clock malfunctions, a clock that depends on the speed of light on its calculation would sure mess up if it travel at speeds close to the speed of light

 

[PeterDonis]

when those clocks are moving faster, they are not ideal or accurate

Look carefully at what I said: we age according to the rate of an ideal clock that follows the same path through spacetime. In other words, we age according to the rate of an ideal clock that is not moving relative to us. (The technical term for this in relativity is "proper time".) The fact that the rate of such a clock looks slower to someone relative to whom it is moving doesn't affect the rate at which we age.

Also, the time dilation of a clock as measured by an observer relative to whom it is moving does not make the clock "inaccurate". As above, it doesn't change the rate at which we age, or at which the clock ticks, at all. It is just a "perspective" effect in spacetime, similar to the way an object's apparent size can change depending on the angle from which you view it.

a clock that depends on the speed of light on its calculation would sure mess up if it travel at speeds close to the speed of light

A light clock doesn't "depend on the speed of light on its calculation". It doesn't "calculate" a rate. It just uses the bouncing of light pulses off a mirror to determine a rate.

i had to give that intro that sounds irrelevant to the topic just to show that I'm open minded.

Are you familiar with the experimental evidence for time dilation? It is at least as strong as the evidence for the quantum phenomena observed in delayed choice and double slit experiments.

 

[Dale]

We can build a variety of clocks using a variety of different frequency standards. If we find that some condition affects one type of clock but not others, then we would say that the clock was inaccurate under those conditions.

However, if all clocks of all mechanisms are affected by exactly the same amount then we may as well say that time itself has changed. There would be no detectable difference between the two, and it is simpler than positing many different effects of the same amount.

The time dilation of relativity corresponds to the second case. We have tested it with clocks based on EM, the strong nuclear force, the weak nuclear force, and gravity. All exhibit time dilation as predicted by relativity.

 

[Crowxe]

Look carefully at what I said: we age according to the rate of an ideal clock that follows the same path through spacetime. In other words, we age according to the rate of an ideal clock that is not moving relative to us. (The technical term for this in relativity is "proper time".) The fact that the rate of such a clock looks slower to someone relative to whom it is moving doesn't affect the rate at which we age.

Also, the time dilation of a clock as measured by an observer relative to whom it is moving does not make the clock "inaccurate". As above, it doesn't change the rate at which we age, or at which the clock ticks, at all. It is just a "perspective" effect in spacetime, similar to the way an object's apparent size can change depending on the angle from which you view it.
A light clock doesn't "depend on the speed of light on its calculation". It doesn't "calculate" a rate. It just uses the bouncing of light pulses off a mirror to determine a rate.
Are you familiar with the experimental evidence for time dilation? It is at least as strong as the evidence for the quantum phenomena observed in delayed choice and double slit experiments.

1. the light clock sounds to depend on the speed of light (the light source, mirror and sensor...etc) if it's 150,000 km between the mirrors then the tick will tick after 1 sec (coz the speed of light is 300,000 km/s) that's my understanding of the light clock

2. I'm familiar with experiment , I've watched different videos much more than i watched the delayed choice, even though the delayed choice more complicated. but maybe there's a catch, the experiment ignore that the light beam should be aimed in angle where the mirror is not there yet, but i assumed the experiment supposes that we aim the light in that certain angle.

3. when i said the clock will not be accurate , that wasnt to an observer or someone beside it , just meant the clock will count the ticks erroneously.

 

[Dale]

light clock sounds to depend on the speed of light

The point of the light clock is that it is easy to analyze. Don't get too hung up on it. The fact is that we have tested clocks of many different operating principles. They all behave as predicted by relativity, regardless of if it is EM, strong, weak, or gravity, or a combination. The evidence really is quite comprehensive and varied.

 

[PeterDonis]

the light clock sounds to depend on the speed of light

The speed of light in vacuum is a physical constant, so saying the clock "depends" on it is saying the clock depends on something that never changes. What's the problem?

the experiment ignore that the light beam should be aimed in angle where the mirror is not there yet

Please give specific references. And not to videos: to textbooks or peer-reviewed papers. (PF has rules on acceptable sources, please review them.) I'm unaware of any such issue with the light clock thought experiment.

just meant the clock will count the ticks erroneously.

And what is your definition of "erroneously"? Remember that, as Dale pointed out, all ideal clocks that follow the same path through spacetime will tick at exactly the same rate. Remember also that according to SR there is no preferred state of motion, so the fact that two clocks in different states of motion tick at different rates does not make one of them "erroneous"; it's just a physical fact that we need to deal with.

 

[Crowxe]

We can build a variety of clocks using a variety of different frequency standards. If we find that some condition affects one type of clock but not others, then we would say that the clock was inaccurate under those conditions.

However, if all clocks of all mechanisms are affected by exactly the same amount then we may as well say that time itself has changed. There would be no detectable difference between the two, and it is simpler than positing many different effects of the same amount.

The time dilation of relativity corresponds to the second case. We have tested it with clocks based on EM, the strong nuclear force, the weak nuclear force, and gravity. All exhibit time dilation as predicted by relativity.

oh... i only know of the one actual experiment done with nuclear watch , no gravity watch if that's the case then i fully accept the theory of dilation . and for now i would just blame the the mirror (light clock) for confusing me

 

[Crowxe]

The speed of light in vacuum is a physical constant, so saying the clock "depends" on it is saying the clock depends on something that never changes. What's the problem?
Please give specific references. And not to videos: to textbooks or peer-reviewed papers. (PF has rules on acceptable sources, please review them.) I'm unaware of any such issue with the light clock thought experiment.
And what is your definition of "erroneously"? Remember that, as Dale pointed out, all ideal clocks that follow the same path through spacetime will tick at exactly the same rate. Remember also that according to SR there is no preferred state of motion, so the fact that two clocks in different states of motion tick at different rates does not make one of them "erroneous"; it's just a physical fact that we need to deal with.

1. the light clock counts time by dividing the distance/speed of light (constant) but if distance changed then it gives different reading
2 erroneously means count wrong to what it should count but dale said all sort of clocks gave the same time variation , so that solves the problem. apparently the hypothetical light clock example is not the best way to introduce someone to relativity and time dialation

 

[PeterDonis]

the light clock counts time by dividing the distance/speed of light

No, it doesn't. It counts time by the number of bounces off the mirrors. We calculate its behavior by dividing the distance between the mirrors by the speed of light, but the clock itself doesn't have to do that; it just works.

erroneously means count wrong to what it should count

And how are you defining what it "should" count? Whether you realize it or not, you are implicitly assuming that there is one preferred state of motion which defines the time a clock "should" count. But relativity says there is no such preferred state of motion. There is no one rate that a clock "should" tick at. There are just ideal clocks moving on their own paths through spacetime, and the time they count depends on the path.

 

[Dale]

oh... i only know of the one actual experiment done with nuclear watch , no gravity watch if that's the case then i fully accept the theory of dilation . and for now i would just blame the the mirror (light clock) for confusing me

Here is one of the best compilations of experimental evidence regarding relativity.

http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

Sections 4 and 5 are particularly relevant, but part of the scientific appeal of relativity is the amazing breadth and depth of data that it explains. A theory that would replace relativity would need to explain all of these results and more.

 

[morrobay]

so the fact that two clocks in different states of motion tick at different rates does not make one of them "erroneous"; it's just a physical fact that we need to deal with.

It was my understanding that stationary clocks and traveling clocks , of any mechanism, all 'tick" at the same rate. Ie. time between ticks. And the traveling clock records less proper time because it traveled a lessor path distance in spacetime.
That Δt' = Δt/γ is referring to total elapsed time.

 

[Herman Trivilino]

Now, for the relativity and time dilation , my argument starts with the light clock, it's designed and calibrated to "count" time in certain conditions same as those large old classic pendulum clocks that are calibrated in certain conditions and they measure time faster in winter as the pendulum rod shrinks or slower during high atmospheric pressure and humidity but we don't age faster in winter nor slower in humid thick air, so why should we say so if a clock that uses different theory gave altered reading??

It's not a real clock, it's a thought experiment designed to demonstrate something about the way real clocks behave. It turns out that real clocks actually do behave this way.

It's true that things don't age faster or slower as a result of the precision issues you mention concerning a pendulum clock. It's also true that things do age differently by precisely the amount predicted by the light clock analysis.

 

[Herman Trivilino]

apparently the hypothetical light clock example is not the best way to introduce someone to relativity and time dialation

It demonstrates that time dilation is a consequence of the invariance of speed $c$.

 

[stevendaryl]

The significance of light clocks is that it demonstrates that a particularly simple way of measuring time that works correctly according to one frame shows time dilation according to another frame. So comparing with a situation in which physical conditions (cold weather) affect a clock's behavior isn't appropriate. The moving clock versus stationary clock is not about two different physical conditions, it is the SAME clock, looked at from two different reference frames.

 

[Crowxe]

The significance of light clocks is that it demonstrates that a particularly simple way of measuring time that works correctly according to one frame shows time dilation according to another frame. So comparing with a situation in which physical conditions (cold weather) affect a clock's behavior isn't appropriate. The moving clock versus stationary clock is not about two different physical conditions, it is the SAME clock, looked at from two different reference frames.

i know that in any experiment that has more than one variable/input , we have to hold all variables to get the measurement we need. in the hypothetical/theoretical light clock,all components are sped up except for the light , causing the distance traveled to be longer and so it's time measuring device that's kinda designed to give different reading as it speeds up. it doesn't make sense unless it's a clock that doesn't count on light or electricity which i found by accident yesterday , what seems to be the undisputed prroof for time dilation , it's the muon measurement , not actually a clock but particles that should decay before it reach the Earth as it gets born on higher atmosphere (and should live only around 22 microseconds) yet we receive it on earth..the particle lives longer due to its nearly speed of light. i now believe the theory but not its proof

 

[Crowxe]

Here is one of the best compilations of experimental evidence regarding relativity.

http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

Sections 4 and 5 are particularly relevant, but part of the scientific appeal of relativity is the amazing breadth and depth of data that it explains. A theory that would replace relativity would need to explain all of these results and more.

thank you for your patience , i'll look into that link and may return with more questions than i already still have :) . i can't absorb what i doubt and i tend to be skeptic or understand things through fighting it rather than getting along with it

 

[PeroK]

what I'm saying is that speed (relative or actual) only affect the clock reading. the clock malfunctions, a clock that depends on the speed of light on its calculation would sure mess up if it travel at speeds close to the speed of light

There's no such thing as something traveling at close to the speed of light. In the light clock thought experiment both clocks are at rest in their own inertial reference frame and both traveling at the speed of light relative to the other. If one messes up, so would the other.

 

[Herman Trivilino]

i know that in any experiment that has more than one variable/input , we have to hold all variables to get the measurement we need. in the hypothetical/theoretical light clock,all components are sped up except for the light , causing the distance traveled to be longer and so it's time measuring device that's kinda designed to give different reading as it speeds up.

It's the same clock viewed by two different observers. One observer is at rest relative to the clock. The other is in motion relative to the clock.

The results of the analysis match what's observed in Nature. That is what it took to convince most physicists that the analysis is correct.

 

[stevendaryl]

i know that in any experiment that has more than one variable/input , we have to hold all variables to get the measurement we need. in the hypothetical/theoretical light clock,all components are sped up except for the light

I don't think you understood my point: It isn't that the clock has been sped up. It's the same clock, looked at from the point of view of another reference frame.

 

[Crowxe]

I don't think you understood my point: It isn't that the clock has been sped up. It's the same clock, looked at from the point of view of another reference frame.

from another frame of reference that sped up ?

 

[jbriggs444]

from another frame of reference that sped up ?

From another reference frame, including one that is inertial and, accordingly, never "sped up".

 

[PeroK]

from another frame of reference that sped up ?

Reference frames are not physical objects. At any time you can look at any physical situation through any reference frame. If you have an aeroplane in flight, you can look at a passenger from the plane's reference frame (passenger sitting still and not moving) or from the ground reference frame (passenger moving at 1000 km/h).

Your contention is that the passenger's wrist watch might stop working because it's traveling at 1000 km/h. But, there is no way to say absolutely that it is the passenger who is moving. In fact, as the Earth is spinning and orbiting the sun, someone on the ground's wristwatch may be traveling much faster - relative to the sun, say.

This illustrates that there is no such thing as absolute velocity. The passenger in the plane is stationary in one frame, moving at 1,000km/h in another, moving at 2,000km/h in another and moving much faster in yet another: 100,000km/h relative to the sun. So, if motion disrupts a wristwatch, none of our watches should work as we orbit the sun at 100,000km/h.

What might disrupt a watch would be acceleration. A watch is more likely to malfunction being rattled on a bicycle at 20km/h than orbiting the sun at 100,000 km/h. Or, there was the long time problem of getting a clock to work at sea. In all cases, it is acceleration and changes in motion that disrupt a mechanism, not pure motion, which cannot in fact be measured.

It is the same with a light clock. One here on Earth would function just the same as one on an aeroplane, just the same as one on a space probe. There is no physical difference in these scenarios that results from a state of absolute motion (or otherwise). That there is no such thing as absolute motion goes back to Galileo, although a lot of people think it came in with Einstein and relativity.

 

[Battlemage!]

i've seen the double slit experiment and the delayed choice . my mind rejected the conclusion, but the experiment setting and configuration of delayed choice is rational and holds water so i accepted the experiment outcome even if it means the world isn't real.

i had to give that intro that sounds irrelevant to the topic just to show that I'm open minded.

Now, for the relativity and time dilation , my argument starts with the light clock, it's designed and calibrated to "count" time in certain conditions same as those large old classic pendulum clocks that are calibrated in certain conditions and they measure time faster in winter as the pendulum rod shrinks or slower during high atmospheric pressure and humidity but we don't age faster in winter nor slower in humid thick air, so why should we say so if a clock that uses different theory gave altered reading??

Special relativity can be seen in Maxwell's equations. That is, it is an electromagnetic theory in a lot of ways. You are made of chemicals. Chemicals are held together by the electromagnetic interaction of protons and electrons. The laws of relativity apply to electromagnetic phenomena. Ergo, they apply to the chemicals that make up your body.

Thus, if relativity affects a clock made of atoms, it affects you too.Edited to add: which brings up an obvious question: if everything we see is held together by electromagnetism, what difference does it make? Every clock of any imaginable type will exhibit behavior in accordance with relativity. It is a small jump to argue that relativity applies to space and time itself, since the results would be identical, and if you make that step you get all the accurate predictions of general relativity too, not to mention the modern formalization of special relativity.

 

[Herman Trivilino]

from another frame of reference that sped up ?

If one observer is in motion relative to another, it's possible that neither of them has ever been sped up. They may have been born that way! Moreover, even if they were born not moving relative to each other, there's no way to distinguish between the one who sped up and the one who didn't.

The Principle of Relativity tells us that there is no way to distinguish between a state of rest and a state of steady motion. You seem to believe that the light clock somehow makes this distinction. It doesn't.

 

[Crowxe]

i'm getting more confused than when i first asked my question (although i found the answer in the Muons)

 

[Dale]

I think that your confusion may be coming from the "geometric" view of relativity, which is very intuitive once you get it but it is a new concept for most people.

The basic idea is that time is another dimension in a combined "spacetime". If you think about plotting it on a piece of paper you might put space as the horizontal axis and time as the vertical axis. The big difference with normal Euclidean geometry is that the appropriate measure of "distance" (called the spacetime interval) is $ds^2=-c^2 dt^2 + dx^2 + dy^2 + dz^2$ instead of the usual Pythagorean theorem.

This view is new, but once you start thinking in geometric terms it makes a lot of things come together.

 

[Crowxe]

Mr. Dale , i can't understand exactly, and it's not your fault , it's me with my scientific degree just high school physics education 26 years ago . but since i was 10 years old i heard about time dilation and accepted it for 34 years until i watched the light clock experiment, it made me reject what i believed . if you explain to me in language that i can't understand then i won't argue and just take your word for granted but i can understand the light clock experiment and i can argue with it (not argue with the relativity theory itself) . anyway thanks to the link you gave me, it doesn't only have the Muons measure but the Doppler experiment too along with others but those two were enough . so i believe in the relativity and apologies to Ernestine for thinking he's reckless . my only problems are :
1. the light clock is an experiment that is loosely designed (maybe it was explained wrong, so i hope you can provide me with link that you approve)
2. there's chaos of not only point of views but also understanding relativity, and that's even clear here if you read the comments

Ps: is there any existing/ongoing experiment that ends the argument of our actual speed and direction of movement

 

[Herman Trivilino]

i'm getting more confused than when i first asked my question (although i found the answer in the Muons)

I think your misunderstanding is in the way you are thinking about moving clocks. When you move with them they behave the same as they do when you're at rest with them. When they're in motion relative to you they behave differently in your rest frame.

A muon's lifetime, as measured in the muon's rest frame, is not increased simply because it's moving relative to you. But in your rest frame its lifetime is increased.

If you are misled by the light clock analysis you'd do well to understand why. The fault does not lie with the light clock.

 

[PeterDonis]

is there any existing/ongoing experiment that ends the argument of our actual speed and direction of movement

How would you test this experimentally?

 

[Crowxe]

I think your misunderstanding is in the way you are thinking about moving clocks. When you move with them they behave the same as they do when you're at rest with them. When they're in motion relative to you they behave differently in your rest frame.

A muon's lifetime, as measured in the muon's rest frame, is not increased simply because it's moving relative to you. But in your rest frame its lifetime is increased.

If you are misled by the light clock analysis you'd do well to understand why. The fault does not lie with the light clock.

i think I'm getting closer and i understand that my clock will always tick at the same intervals that mind is used to. but still have couple of basic questions to clear misconception in my mind caused by the light clock .

in the light clock, the experiment display a change in the light beam direction leaning towards the direction of movement instead of staying perpendicular to the mirror. There's a difference between the track it should take to meet the mirror and the actual track it should take according to light behavior unless the experiment states that light will behave as ping pong ball bouncing up and down between train's floor and sealing because it gained horizontal speed from the train. to my understanding, the light shouldn't behave like that and it doesn't gain speed from its source's speed

 

[PeroK]

i think I'm getting closer and i understand that my clock will always tick at the same intervals that mind is used to. but still have couple of basic questions to clear misconception in my mind caused by the light clock .

in the light clock, the experiment display a change in the light beam direction leaning towards the direction of movement instead of staying perpendicular to the mirror. There's a difference between the track it should take to meet the mirror and the actual track it should take according to light behavior unless the experiment states that light will behave as ping pong ball bouncing up and down between train's floor and sealing because it gained horizontal speed from the train. to my understanding, the light shouldn't behave like that and it doesn't gain speed from its source's speed

It's interesting that this question seems to come up a lot. The beam of light can only do one thing. If it bounces up and down between the mirrors, it bounces up and down between the mirrors. That is a physical fact. If you are at rest with respect to the mirrors, then you see that as vertical motion. But, if you moving with respect to the mirrors, you see that as a zig-zag motion.

The light beam can't be vertical in your frame and vertical in its rest frame at the same time.

 

[PeroK]

PS The key to why the constant speed of light, independent of the motion of the source leads to SR is contained in this fact. If the source is moving and you see the light go at a diagonal, then the vertical component of its velocity must be less than the speed of light. But, for someone at rest wrt to light clock, the vertical component must be the full speed of light.

The two observers will, therefore, measure different values for the vertical speed of the beam - and that leads to time dilation.

In contrast, if the speed of light depended on its source, like a ball being thrown up, the ball would be moving faster to the observer watching the train go by. In fact, in this case, if you don't throw the ball, the observer with the ball measures its speed to be 0, while the observer watching the ball go past measures the speed of the ball as the same as that of the train.

 

[Crowxe]

How would you test this experimentally?

i was asking if there's any but since you asked then i'll share my naive idea if the following are true facts
1. if light speed is constant in a medium regardless to the source speed
2. if that speed varies between one medium and a nother

so it could be done as follows:

if light speed in vacuum is 300,000 km/s and is 151,000 km/s in another medium . we can emit light through both mediums at same moment and have two detectors at same distance say 300,000 km away from the source (that distance is measured by time from our own perception , so I'm still within relativity point of view).

if we measure the time difference and then rotate the whole setting 180 degrees in x plan or 90 degrees in y plan , then maybe get different time shift (because the experiment is moving but we just don't know to what direction).

i did the calculation for that example based on the system at absolute rest then at speed 150,000 km/s. first time shift was 0.5 seconds and the second shift was 148 seconds (without taking time dilation in consideration) or 172 seconds with time dilation but i think we should count on our perception at that speed and say 148 seconds

 

[Crowxe]

It's interesting that this question seems to come up a lot. The beam of light can only do one thing. If it bounces up and down between the mirrors, it bounces up and down between the mirrors. That is a physical fact. If you are at rest with respect to the mirrors, then you see that as vertical motion. But, if you moving with respect to the mirrors, you see that as a zig-zag motion.

The light beam can't be vertical in your frame and vertical in its rest frame at the same time.

i understand what you're saying, the two observers , time dilation and constant speed of light but i need one point addressed . the ping pong ball bouncing in a train adopts the train horizontal velocity , that's why it's vertical to the man on board and diagonal to the observer. but light aimed vertically will continue travel vertically (every segment of it travel vertically but the over all path should be diagonally backward in respect to the moving ship) we can't add horizontal or any speed to the light by moving the source

 

[Crowxe]

i must declare that i had doubts in time dilation but now i fully understand it and it even makes sense . the continuation of this thread is only related to the light behavior in the light clock

 

[PeroK]

i understand what you're saying, the two observers , time dilation and constant speed of light but i need one point addressed . the ping pong ball bouncing in a train adopts the train horizontal velocity , that's why it's vertical to the man on board and diagonal to the observer. but light aimed vertically will continue travel vertically (every segment of it travel vertically but the over all path should be diagonally backward in respect to the moving ship) we can't add horizontal or any speed to the light by moving the source

In that case, the light would have to go in two different (physical) directions at the same time. Imagine the man on board aims the light at a target. It either hits the target or it doesn't. It can't hit the target according to one observer and miss according to another. The light must follow the same physical path in both cases. You could define the path to be a series of hoops that the light passes through. It either passes through each physical hoop or it doesn't.

The "direction" of the motion of the light must be different in the two different frames, as the definition of "vertical" motion depends on the frame.

Forget the source for a moment. Just imagine a beam of light and two observers, standing together. Let's say the beam is moving vertically away from the two. One observer starts to move to the right. Now he is in a different frame and, as he moves, the light no longer moves vertically to him. From his new reference frame it is moving vertically and to the left.

The second observer still sees the light take the same physical path - and pass through the same physical hoops. But, now, to him the hoops are moving and the path is diagonal.

Finally, you have made an interesting and quite common misinterpretation of the constancy of the speed of light. That somehow the light can be "vertical" to two different observers, whose definition of vertical motion is different! Even light can't do that.

 

[stevendaryl]

in the light clock, the experiment display a change in the light beam direction leaning towards the direction of movement instead of staying perpendicular to the mirror. There's a difference between the track it should take to meet the mirror and the actual track it should take according to light behavior unless the experiment states that light will behave as ping pong ball bouncing up and down between train's floor and sealing because it gained horizontal speed from the train. to my understanding, the light shouldn't behave like that and it doesn't gain speed from its source's speed

If you're on a train moving at a constant speed, and you start bouncing a basketball up and down, then to you, it is traveling a path that is perpendicular to the floor. To someone outside the train, the basketball travels a diagonal path. Light is no different in this respect. So the conclusion is that the angle that the bouncing object follows is relative to the rest frame of the observer. Special Relativity is no different from pre-relativistic physics in this regard.

I understand the intuition: In the light clock, when the clock is moving, it appears that the light must be "aimed" ahead of the mirror. But the same thing is true of the person bouncing a basketball inside a moving train: From the perspective of someone at rest looking at the train move past, it seems that the person with the basketball must "aim" it slightly ahead of the point on the floor where he wants it to hit. But the person aboard the train isn't doing anything differently than if the train were at rest.

 

[Crowxe]

In that case, the light would have to go in two different (physical) directions at the same time. Imagine the man on board aims the light at a target. It either hits the target or it doesn't. It can't hit the target according to one observer and miss according to another. The light must follow the same physical path in both cases. You could define the path to be a series of hoops that the light passes through. It either passes through each physical hoop or it doesn't.

The "direction" of the motion of the light must be different in the two different frames, as the definition of "vertical" motion depends on the frame.

Forget the source for a moment. Just imagine a beam of light and two observers, standing together. Let's say the beam is moving vertically away from the two. One observer starts to move to the right. Now he is in a different frame and, as he moves, the light no longer moves vertically to him. From his new reference frame it is moving vertically and to the left.

The second observer still sees the light take the same physical path - and pass through the same physical hoops. But, now, to him the hoops are moving and the path is diagonal.

Finally, you have made an interesting and quite common misinterpretation of the constancy of the speed of light. That somehow the light can be "vertical" to two different observers, whose definition of vertical motion is different! Even light can't do that.

thanks for the effort and explaining , it cleared a lot of the confusing things to me . if you still have energy left , i would like to tweak a bit the example that you put here.

lets say it's one observer with light beaming vertically to the plan he's standing on and then him along with the light source gained speed horizontally , he and the light source gained horizontal speed but did the light gain that horizontal speed?

 

[Crowxe]

If you're on a train moving at a constant speed, and you start bouncing a basketball up and down, then to you, it is traveling a path that is perpendicular to the floor. To someone outside the train, the basketball travels a diagonal path. Light is no different in this respect. So the conclusion is that the angle that the bouncing object follows is relative to the rest frame of the observer. Special Relativity is no different from pre-relativistic physics in this regard.

I understand the intuition: In the light clock, when the clock is moving, it appears that the light must be "aimed" ahead of the mirror. But the same thing is true of the person bouncing a basketball inside a moving train: From the perspective of someone at rest looking at the train move past, it seems that the person with the basketball must "aim" it slightly ahead of the point on the floor where he wants it to hit. But the person aboard the train isn't doing anything differently than if the train were at rest.

there's one significant difference comparing the bouncing ball and the bouncing beam regarding the direction (according to the person in the same reference frame) . the ball can gain the train's horizontal speed but light can't gain speed

 

[stevendaryl]

there's one significant difference comparing the bouncing ball and the bouncing beam regarding the direction (according to the person in the same reference frame) . the ball can gain the train's horizontal speed but light can't gain speed

Well, there is the speed in the horizontal direction, and there is the speed in the vertical direction. The total speed (which is defined by: (total speed)² = (horizontal speed)² + (vertical speed)²) is constant, but light can change its horizontal speed.

 

[Crowxe]

Well, there is the speed in the horizontal direction, and there is the speed in the vertical direction. The total speed (which is defined by: (total speed)² = (horizontal speed)² + (vertical speed)²) is constant, but light can change its horizontal speed.

thats a simple language i can understand , so the horizontal speed is through aiming the beam forward or gained by the horizontal source movement ? (i believe in both cases time dilation will take place and relativity should still hold)

 

[PeroK]

thanks for the effort and explaining , it cleared a lot of the confusing things to me . if you still have energy left , i would like to tweak a bit the example that you put here.

lets say it's one observer with light beaming vertically to the plan he's standing on and then him along with the light source gained speed horizontally , he and the light source gained horizontal speed but did the light gain that horizontal speed?

Yes, because it's all about reference frames. If the light (or anything) is moving vertically in his frame of reference, then it must be moving vertically and horizontally in another frame of reference in which he and the light source are moving horizontally. That's essentially a physical/geometric reality - and, in fact, has to do with all physics, not just relativity.

It's better not to think about the light source or light "gaining" horizontal speed, but to see that it has a horizontal component to its motion in one frame. If its horizontal speed in frame A is 0, then in a frame B moving horizontally at speed $v$ with respect to frame A, its horizontal speed must be $v$.

This was standard, classical physics from Netwon's time at least. In classical physics, you can then take the vertical speed $w$, say. which is the same in both frames and then:

The speed of the object is $w$ in frame A.

The speed of the object is $\sqrt{w^2 + v^2}$ in frame B.

However, there was experimental evidence that if the "object" was a beam of light, then this did not apply. In particular:

The speed of the light is $c$ in frame A.

The speed of the light is $c$ in frame B. It is not $\sqrt{c^2 + v^2}$.

This was a terrible puzzle for classical physics. By using this experimental fact and his light-clock thought experiment, Einstein showed that one explanation was that "time itself was suspect" and that with respect to one frame, time in the other frame is dilated by the factor of $\frac{c}{\sqrt{c^2 + v^2}}$.

This time dilation explains why, even thought the observer in frame A sees the light moving only vertically and B sees the light moving vertically and horizontally, they measure the same speed $c$.

There was never any thought that somehow the light was moving vertically in both frames.

 

[PeroK]

there's one significant difference comparing the bouncing ball and the bouncing beam regarding the direction (according to the person in the same reference frame) . the ball can gain the train's horizontal speed but light can't gain speed

It can't increase its speed, but its speed will and must have a horizontal component in some frames! You need to give up this idea that light can only travel vertically!

 

[Crowxe]

Yes, because it's all about reference frames. If the light (or anything) is moving vertically in his frame of reference, then it must be moving vertically and horizontally in another frame of reference in which he and the light source are moving horizontally. That's essentially a physical/geometric reality - and, in fact, has to do with all physics, not just relativity.

It's better not to think about the light source or light "gaining" horizontal speed, but to see that it has a horizontal component to its motion in one frame. If its horizontal speed in frame A is 0, then in a frame B moving horizontally at speed $v$ with respect to frame A, its horizontal speed must be $v$.

This was standard, classical physics from Netwon's time at least. In classical physics, you can then take the vertical speed $w$, say. which is the same in both frames and then:

The speed of the object is $w$ in frame A.

The speed of the object is $\sqrt{w^2 + v^2}$ in frame B.

However, there was experimental evidence that if the "object" was a beam of light, then this did not apply. In particular:

The speed of the light is $c$ in frame A.

The speed of the light is $c$ in frame B. It is not $\sqrt{c^2 + v^2}$.

This was a terrible puzzle for classical physics. By using this experimental fact and his light-clock thought experiment, Einstein showed that one explanation was that "time itself was suspect" and that with respect to one frame, time in the other frame is dilated by the factor of $\frac{c}{\sqrt{c^2 + v^2}}$.

This time dilation explains why, even thought the observer in frame A sees the light moving only vertically and B sees the light moving vertically and horizontally, they measure the same speed $c$.

There was never any thought that somehow the light was moving vertically in both frames.

thanks a lot , you've been great help , i think I'm confusion free for now

 

[stevendaryl]

thats a simple language i can understand , so the horizontal speed is through aiming the beam forward or gained by the horizontal source movement ? (i believe in both cases time dilation will take place and relativity should still hold)

A mirror that is oriented vertically cannot change the light's horizontal speed. So if the light is initially traveling vertically, it'll keep traveling vertically. If it is initially traveling at a diagonal, it will keep traveling diagonally. After bouncing off the mirror, the only change is to the vertical velocity: that switches direction.

So the mirror doesn't need to "aim" for where the light should go.

Now, you could ask the question of how the light gets started traveling diagonally, in the first place. Although it's maybe not intuitive, the fact is that if the person on the train takes an ordinary flashlight, and aims it straight up, the light coming out of the flashlight will travel "diagonally" as seen from someone outside the train.

 

[Crowxe]

A mirror that is oriented vertically cannot change the light's horizontal speed. So if the light is initially traveling vertically, it'll keep traveling vertically. If it is initially traveling at a diagonal, it will keep traveling diagonally. After bouncing off the mirror, the only change is to the vertical velocity: that switches direction.

So the mirror doesn't need to "aim" for where the light should go.

Now, you could ask the question of how the light gets started traveling diagonally, in the first place. Although it's maybe not intuitive, the fact is that if the person on the train takes an ordinary flashlight, and aims it straight up, the light coming out of the flashlight will travel "diagonally" as seen from someone outside the train.

i guess the confusion is almost gone but i'll just state it again in case it wasnt clear. i wasnt talking about 2 farme references , just the one on the train and my prediction was the light beam would appear diagonally backward to him