# Relativity doubts

#### meteor

I'm not sure that i'm going to understand relativity someday. Well, I can comprehend that each frame of reference has its own time. But for me time is not something physical, I believe that time is simply the velocity with which physical phenomena occurs. If i am travelling with a clock, then the hands of the clock will rotate more slow than if I am at rest.
Then I imagine two points A and B, and a beam of photons that made his way crossing first point A and then point B. I am at certain distance, for example point C. When a photon pass through point A, I click my chronometer, and stop the chronometer when the photon pass through point B. Perfect, 5 seconds for example.
Now, imagine that I'm going to repeat the experiment. I'm in point C.
But when the photon cross through point A,I click the chronometer and then I start a little trip, and return at point B just in the moment that the photon pass through point B, and I stop the chronometer. During the trip, the chronometer must have been going slowest than in rest, then now I've measured another time for the voyage of the photon from A to B I've measured 2 differents velocities for the light!
I'm misconcepting something? I would appreciate any help.

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#### chroot

Staff Emeritus
Gold Member
Originally posted by meteor
If i am travelling with a clock, then the hands of the clock will rotate more slow than if I am at rest.
Wrong. If you're travelling in a comoving frame with the clock, then you will never notice anything funny going at all. The clock will operate, in every way, normally.
When a photon pass through point A, I click my chronometer, and stop the chronometer when the photon pass through point B.
You can't do this. When you're at point C, you can't say exactly what's happening at what time at point A or B. You'd have to involve the period of time it took the message to travel to you from those points.
I've measured 2 differents velocities for the light!
This is also false. The length of the spacetime interval (think of it as a distance in space-time) between any two events is constant, and all observers will always agree on that length.

You're still getting caught up in the idea that "going fast makes time slow down," which is a butchered statement.

- Warren

#### meteor

Wrong. If you're travelling in a comoving frame with the clock, then you will never notice anything funny going at all. The clock will operate, in every way, normally.
yes,I will not notice nothing strange, because my neurons, will go slower than commonly, and I will think that all is going OK. But this
doesn't change that INDEED, the chronometer is going more slow than in rest, so I still believe that I will measure two different times.

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#### chroot

Staff Emeritus
Gold Member
Originally posted by meteor
yes,I will not notice nothing strange, because my neurons, will go slower than commonly, and I will think that all is going OK. But this
doesn't change that INDEED, the chronometer is going more slow than in rest, so I still believe that I will measure two different times.
This is incorrect. I'm not going to say it again.

- Warren

#### jammieg

I don't understand general relativity also.
I mean I get it, but what good is it? I mean if were the complete truth then why are many people searching for a quantum gravity theory that unifies all the forces and shows relationship?

I asked my brother(a musician), "if you were travelling at the speed of light next to someone else travelling at the speed of light what would you see?".
He replied, "well if you were moving at the speed of sound next to someone moving at the speed of sound would you hear them?".

I posted my take on GR in topic "time is what what?" by Tesla, maybe it'll give you another way of viewing it Meteor maybe not. To me GR explains how time and gravity relate very well but not how gravity works, not it's relationship to the other forces.

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#### chroot

Staff Emeritus
Gold Member
Originally posted by jammieg
I mean I get it, but what good is it?
It provides correct predictions to a lot of experiments to which Newtonian gravity does not.
I mean if were the complete truth then why are many people searching for a quantum gravity theory that unifies all the forces and shows relationship?
It most certainly is not "the complete truth." At the very least, it is incompatible with quantum mechanics. Eventually a theory will have to be created that unifies the two in a physically verifiable way. This would be called the 'grand unified' theory. While we're making rapid progress, this theory is still beyond us.

- Warren

#### meteor

Which is the physical explanation for the FitzGerald-Lorentz contraction? That is, why the dimensions of an object reduces at high velocities?
The same for the mass, why the mass of an object augment with the velocity?

#### chroot

Staff Emeritus
Gold Member
You essentially just asked me to teach you the whole of relativity theory, which I do not have the time to do. I suggest you buy any of the great number of good introductory books on the subject, or browse some of the many good websites.

- Warren

#### newton1

Originally posted by meteor
yes,I will not notice nothing strange, because my neurons, will go slower than commonly, and I will think that all is going OK. But this
doesn't change that INDEED, the chronometer is going more slow than in rest, so I still believe that I will measure two different times.
no no.....
you will not measure the two different time
because you still go with your reference frame
you slow down, and the clock also
you and clock are in the same reference frame
the two different time will occur when the other people try to measure your time when you are moving but he are not

#### RuroumiKenshin

Originally posted by meteor
yes,I will not notice nothing strange, because my neurons, will go slower than commonly, and I will think that all is going OK. But this
doesn't change that INDEED, the chronometer is going more slow than in rest, so I still believe that I will measure two different times.

Relativity describes a universe where everything is relative. So for you, time flows 'normally' and you only appear to be moving in slow motion to someone else; that doesn't mean you are in your perspective. Comprehendo?

#### meteor

So for you, time flows 'normally' and you only appear to be moving in slow motion to someone else; that doesn't mean you are in your perspective. Comprehendo?
No, I don't comprehend. I think that if somebody see me moving in slow motion, is because i'm really moving in slow motion (and my neurons too). But well, i will try to learn more about relativity and i will tell you.

#### chroot

Staff Emeritus
Gold Member
Originally posted by meteor
No, I don't comprehend. I think that if somebody see me moving in slow motion, is because i'm really moving in slow motion (and my neurons too). But well, i will try to learn more about relativity and i will tell you.
You see a tree in the forest -- a great tall one. Say you're half a mile from the tree -- it looks rather small.

Say your friend Sam is right at the base of the tree. To him, the tree looks extremely large.

How is it possible that the tree looks small to you and large to him? After all, it's the same tree -- right?

- Warren

#### nbo10

Originally posted by jammieg
I mean I get it, but what good is it?

Well if GR/SR wasn't correct or we did not understand it, GPS systems that we use for almost all navigation would not operate correctly. Planes and boats would end up 1000's of miles from were they're suppose to be. Physics Today May 2002 had a very good article on GPS system and corrections for relativity.

JMD

#### jammieg

Thanks for correcting me on that, surely there are lots of uses I don't have a clue about. GR is what I feel leaves too many unaswered questions to be the whole truth.

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#### RSM1000

Originally posted by meteor
I'm not sure that i'm going to understand relativity someday. Well, I can comprehend that each frame of reference has its own time. But for me time is not something physical, I believe that time is simply the velocity with which physical phenomena occurs.
If you're going to use your own definition of time, rather than what time is, then you surely won't understand relativity.

Originally posted by meteor
If i am travelling with a clock, then the hands of the clock will rotate more slow than if I am at rest.
No, if you travel with a clock, it will not matter weather you're moving or still.

Originally posted by meteor
Then I imagine two points A and B, and a beam of photons that made his way crossing first point A and then point B. I am at certain distance, for example point C. When a photon pass through point A, I click my chronometer, and stop the chronometer when the photon pass through point B. Perfect, 5 seconds for example.
The time that the photon passes A for the photon is not the same time that the photon passes A from any other position at all whatsoever in the entire universe, including your point at C.

Originally posted by meteor
Now, imagine that I'm going to repeat the experiment. I'm in point C.
But when the photon cross through point A,I click the chronometer and then I start a little trip, and return at point B just in the moment that the photon pass through point B, and I stop the chronometer. During the trip, the chronometer must have been going slowest than in rest, then now I've measured another time for the voyage of the photon from A to B I've measured 2 differents velocities for the light!
I'm misconcepting something? I would appreciate any help.
I would question where you ever read about reletivity, as pretty much everything you said was incorrect. I hope you didn't have a teacher this poor at making you understand? I would recommend you pick up a reletivity book!

#### nbo10

Quote:
GR is what I feel leaves too many unaswered questions to be the whole truth.

Hardly any theory will explain any and everything. It explains what we know now and maybe what we will discover in the future, if not it will be modified or replaced all together.

JMD

#### RSM1000

Originally posted by nbo10
Quote:
GR is what I feel leaves too many unaswered questions to be the whole truth.

Hardly any theory will explain any and everything. It explains what we know now and maybe what we will discover in the future, if not it will be modified or replaced all together.

JMD

When a scientist so adamantly proclaims a claim to fact, she (or he) means that it is a fact NOW, and will work with any data involved. But it is not always a fact.

#### meteor

I would question where you ever read about reletivity, as pretty much everything you said was incorrect. I hope you didn't have a teacher this poor at making you understand? I would recommend you pick up a reletivity book!
I have read some books. For example, in "The universe in a nutshell",S.Hawking, page 6, puts that the clocks slow down when they are not at rest. This is what i'm saying!
And what happen with the twin paradox? One twin is in earth, and the other returns to the earth after a trip for the universe. When return to the earth, the traveller twin is younger that its earthbound twin, but this is because he has been travelling at high velocity and then the biological processes in his body has been occurring at slow rapidity, I think

#### RSM1000

Originally posted by meteor
I have read some books. For example, in "The universe in a nutshell",S.Hawking, page 6, puts that the clocks slow down when they are not at rest. This is what i'm saying!
And what happen with the twin paradox? One twin is in earth, and the other returns to the earth after a trip for the universe. When return to the earth, the traveller twin is younger that its earthbound twin, but this is because he has been travelling at high velocity and then the biological processes in his body has been occurring at slow rapidity, I think
Then I suppose you're seriously misunderstanding the concept.

The twins don't age any faster or slower at all reletive to themselves.

It's just reletive to eachother that things change.

You must remember the difference between you to yourself, and you to anything other than yourself.

You're just missing the concept of reletivity.

An event appears different from wherever in the universe you percieve the event, no two points view it the same way.

#### newton1

Originally posted by meteor
I have read some books. For example, in "The universe in a nutshell",S.Hawking, page 6, puts that the clocks slow down when they are not at rest. This is what i'm saying!
And what happen with the twin paradox? One twin is in earth, and the other returns to the earth after a trip for the universe. When return to the earth, the traveller twin is younger that its earthbound twin, but this is because he has been travelling at high velocity and then the biological processes in his body has been occurring at slow rapidity, I think
this is about the different frame
the twin parodox is a result from 2 different reference frame
the time is relativity
just like the velocity
you saw A move fast, but the other people saw that maybe slow
i think you must make clear of "what is the relativity"
if not, you will never understand this theory

#### chroot

Staff Emeritus
Gold Member
Originally posted by meteor
I have read some books. For example, in "The universe in a nutshell",S.Hawking, page 6
This is not a book that will teach you relativity. It's a load of steaming hot crap sandwiched between two covers. These books sadly always seem to make more confusion for their readers, rather than less.

Go pick up a copy of Feynman's Lectures on Physics. Volume I alone will do. Read it. Or a copy of any of the introductory first year collegiate physics texts, like Halliday and Resnick.

- Warren

#### meteor

I only have a question (and the answer is very simple, yes or no)
It's time something physical (it's made of some kind of matter, have some kind of structure, etc)?

#### chroot

Staff Emeritus
Gold Member
It it not composed of matter, but does have structure -- you can measure it, for example.

- Warren

#### jammieg

There's a nice introductory book that I still refer back to called "Six easy pieces & six not so easy pieces"-Feynman. Even though it's rather an outline of physics not the details, not advanced physics, it definitely satisfied my curiousity.

Tesla got me thinking about time and gravity and the ether and I had this vague outline of how gravity slowed time maybe I forgot something but anyway here's my take on it:

Time is a word we use to define the motion of atoms in the clock hand from point a to point b, usually it takes the same time for the clock hand to traverse that distance and so we call it a minute of time having passed, but add a little heat to the winding spring and the next minute may pass a bit faster (maybe only a 1000th of a second), so you see time is relative and the universe doesn't care about the past or future it is only atoms moving about at various speeds acting upon causes.
How does gravity slow time? In my view it doesn't so much as it is slowing the atomic motion of the atom by forcing it to move in a way counter to it's heat or kinetic motion, but gravity is so weak that the differences in time of a clock in space to a clock on Earth are extremely small, however move an atom at near the speed of light and it is being forced to move counter it's kinetic energy in a big way and so time slows down for that atom, that is it will try to maintain it's existence such that the electron is not moving around the proton at near the speed of light to reach the speed of light and explode to become light. In other words if an electron is moving around a proton at 1/10th the speed of light and the whole atom is moving at 99% the speed of light the electon for some reason, maybe ether, try to counter it's motion and avoid becomming light, so basically the electron and proton will move very slowly at whatever they are doing and the clock hand will move very slowly as a consequence.
Is this close to the truth or where did I go astray? I honestly can't remember...the bits and pieces of where I read this or if I imagined it.

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