Time Measurement: How Is Time Measured?

[bodhi]

how is time measured? if time is 1 sec distance traveled by light is 3 lakh km for that time is "c" now if we overcome this speed we have to go into future,but the problem here is we take light as a reference,had we not taken light as a reference in measurement of time,there would have been no question of getting into future.
i believe contraction and expansion of time takes place only due to our reference i.e "c",and by the way what proves speed of light is fastest?
i really feel traveling in future is immpossible,are there any proofs?


please let me know.

 

[tiny-tim]

welcome to pf!

hi bodhi! welcome to pf!

how is time measured? if time is 1 sec distance traveled by light is 3 lakh km for that time is "c" now if we overcome this speed we have to go into future,but the problem here is we take light as a reference,had we not taken light as a reference in measurement of time,there would have been no question of getting into future.

yes, that's correct, we take the speed of light as a reference for measuring time and distance …

essentially we use the "radar" method … the distance of an object is half the difference between the times on our clock when the "radar" leaves and returns, and the time of an object is the time on our clock halfway between those two times

if for example a stationary source projects a shadow of an object moving North onto a screen so that the shadow moves slower than light, then (obviously!) we regard the shadow as moving North, but if the screen is placed so far away that the shadow moves faster than light, then (equally obviously!) we still regard the shadow as moving North … there is no question of the shadow moving backwards in time

(of course, moving faster than light is possible only for non-material things such as shadows )

i believe contraction and expansion of time takes place only due to our reference i.e "c",and by the way what proves speed of light is fastest?

experiment confirms it … when we accelerate a massive object (such as an electron) close to the speed of light, it behaves exactly as if the speed of light is the limit

i really feel traveling in future is immpossible,are there any proofs?

do you mean traveling into the future?

travelling into the future is easy, we do it all the time, traveling into the past would be an achievement!

 

[nitsuj]

travelling into the future is easy, we do it all the time, traveling into the past would be an achievement!

yea that's for sure, but what about in the sense that time on the moon would pass more quickly then on earth, when heading back to home frame you would be older then if you had just stayed on earth. maybe that's traveling to the past, lol j/k



"i really feel traveling in future is immpossible,are there any proofs?"

If I get what you are saying, I'd say yes it is impossible to travel into the future. In the sense that nothing goes faster then c.

Going into the "future" means going "slower" (time dilation) then the frame you want to get to the future in.

They way I read your statement it sounds more like traveling into the past.



No one can travel "ahead" of "c", i.e. the meaning of "future" as I read in your statement.

 

[bodhi]

thanks a lot sir,but i wish to kno how do we travel future very often.

 

[tiny-tim]

you're doing it now!

how can you stop traveling itno the future? ​

 

[nitsuj]

thanks a lot sir,but i wish to kno how do we travel future very often.

Life time Airline pilots probably accumulate the greatest "time" variance compared to common folk. (Edit: actualy spacestation peeps, from gravity differences to earth, probably accumulate the greatest variance)

Would be neat to see if it would amount to a second over a pilots career.

 

[ZealScience]

In relativity a synchronization is introduced, in relativity when you measure any thing, time length, you got to synchronize the clocks. What synchronizes the clock? Light.

The question of yours is actually not valid in special relativity, because firstly the speed limit is because of causality, which means "reason" happens before "results". But if you travels into future it sounds like you are able to happen after your result which is not valid.

However, using what have been derived, E=mc^2, you can see that mass is increasing in a logistic manner because of kinetic energy which is E=1/2mv^2. While approaching c, mass increases a lot which means kinetic is greater, more kinetic would mean more mass!

 

[questionator89]

I am dealing with a similar question in another thread, and many questions come of the answers you get when you think about these things.

So firstly the closer you get to the speed of light the slower time goes.
You don't perceive time to be going slower, you always feel one second per second.

So let's imagine you traveled in an orbit around the sun at 60% of the speed of light then returned to earth, you will have experienced a time shift between you and earth.
While one hour passed for you to rip around in your spaceship, 5 days has passed on earth.

You have just time traveled 4 days and 23 hours into the future.

Heres the thing about the speed of light though:
When we do equations to figure out how much energy it would take to reach the speed of light we reach a conundrum.
Not only do you age slower at a faster momentum, but you also gain mass.
At one point the faster we go the more mass we gain which needs more energy to move it which creates more mass which then needs more energy to move it which creates more mass...

Apparently if you try to reach the speed of light you would need an infinite amount of energy to move an infinite amount of mass and it just doesn't work.

Also, if we were to try to surpass the speed of light, this means that before we do that we actually reach the speed of light.
Forget about the infinity thing let's say we just say F it and do it.
At the speed of light time stops.
Let me explain what this really means.
Lets say you are a photon, your a cool dude your name is Jeff the photon. Let's pretend you live in a whole universe of mirrors and one brick wall.
Because time doesn't accumulate for you, this means you will perceive hitting all the mirrors you would hit along your journey and finally the brick wall SIMULTANEOUSLY at the speed of reality.
No time will have passed for you in between objects.

the strange thing about this is that light is suuuuuuuper slow.
It takes 8 minuits for the light from the sun to reach the earth.

We would experience jeff moving through space for a very very very... long time. those verys could have continued, trust me.

So let's say we as space travelers try to reach the speed of light and fail, even if we only get kinda close to the speed of light, the whole universe could have aged to death around us and we would have no clue.
So to add to the conundrum::
If the closer we get to the speed of light the slower time starts accumulating,
then the farther we get away from traveling at the speed of light, the faster time must accumulate.
Right?

What this implies is that the momentum we are going determines what rate of time we feel according to this law.

Which means we must be able to slow down enough to experience a whole bunch more time, relative to what Earth would feel.

in fact if we could slow something down to where it has no momentum, no mass, it would age to infinity.

But where does the time boundary get drawn between objects in motion? When they are not connected in any way and experiencing different momentums right?

so let's say we drop a clock off behind Earth in orbit and try to make it not move.
Then on our way around the sun, one year later, we pick this clock up.
What we find is that this clock has accumulated 1.0000000345 seconds for every Earth second.
so it has aged slightly more than we did
So obviously this means that it wasnt at rest. if it were at rest it would have aged much more.

So obviously this means that our sun is moving right?
or maybe obviously this means that our galaxy is moving right??

but here's the thing

If this were true, and we could change time, and do all these things I am talking about,

then we would be able to launch our clock in the opposite direction of whichever way we are traveling that gives us the ability to not age into infinty, and our clock would age more.
\
If we CAN'T launch a clock in a particular direction and cause it to age faster (by actually slowing its momentum)
Then this means that our universe has a base limit at which time can accumulate, or that our whole universe has a built in momentum that keeps it from aging to infinity.
possibly the expansion of the universe? who knows

there's so much more that this law would imply if it were actually the case but this post is too long
thank you and goodnight

 

[Drakkith]

Heres the thing about the speed of light though:
When we do equations to figure out how much energy it would take to reach the speed of light we reach a conundrum.
Not only do you age slower at a faster momentum, but you also gain mass.
At one point the faster we go the more mass we gain which needs more energy to move it which creates more mass which then needs more energy to move it which creates more mass...

Despite what has been said in this thread, you do not gain mass as you accelerate. Mass means "invariant mass". This mass would be agreed upon by all observers measuring you no matter how fast you go. Your momentum and kinetic energy will continue to increase without limit as you continue to accelerate, however.

in fact if we could slow something down to where it has no momentum, no mass, it would age to infinity.

Objects always have mass. Light is the only known massless object. And it always travels at c.

so let's say we drop a clock off behind Earth in orbit and try to make it not move.
Then on our way around the sun, one year later, we pick this clock up.
What we find is that this clock has accumulated 1.0000000345 seconds for every Earth second.
so it has aged slightly more than we did
So obviously this means that it wasnt at rest. if it were at rest it would have aged much more.

The clock was never at rest to begin with. You'd need to provide continual acceleration to keep it from being pulled into the Sun, meaning this is NOT an inertial frame of reference. Guess what this causes. Time dilation.

So obviously this means that our sun is moving right?
or maybe obviously this means that our galaxy is moving right??

Both are true, but the way the clock works would tell you nothing about the Sun and the Galaxy's movement relative to other objects.

Then this means that our universe has a base limit at which time can accumulate, or that our whole universe has a built in momentum that keeps it from aging to infinity.
possibly the expansion of the universe? who knows

No. It's simply a fact that time passes at exactly 1 second per second for all observers in their own frame of reference.

However, using what have been derived, E=mc^2, you can see that mass is increasing in a logistic manner because of kinetic energy which is E=1/2mv^2. While approaching c, mass increases a lot which means kinetic is greater, more kinetic would mean more mass!

It's more appropriate to use the full form of Einsteins equation and use momentum instead of kinetic energy. Otherwise things get confusing, like thinking that mass increases with velocity.

 

[questionator89]

Could we in the situation where we are trying to make the clock at rest (in respect to the earth, and in respect to the sun which is also at rest in respect to the earth) account for the acceleration away from the sun it would undergo to keep at a fixed location? I would be surprised if its time dilation were exactly the same as the Earth's which orbited the sun.

I doubt there is any part of space which is not subject to gravitational fields. If the strength of the field was known could it be accounted for?

 

[Drakkith]

Could we in the situation where we are trying to make the clock at rest (in respect to the earth, and in respect to the sun which is also at rest in respect to the earth) account for the acceleration away from the sun it would undergo to keep at a fixed location? I would be surprised if its time dilation were exactly the same as the Earth's which orbited the sun.

What? The Earth cannot be at rest with the Sun, we are orbiting it. Do you understand what "at rest" means?


I doubt there is any part of space which is not subject to gravitational fields. If the strength of the field was known could it be accounted for?[/QUOTE]

The only reason I bring up the fact that the clock would not be in an inertial frame is because you seem to have drawn some very incorrect conclusions from this premise. Honestly, you're better off just sticking to simple scenarios and not thinking about orbiting objects. It just gets complicated.

 

[questionator89]

Again, i want to ask... So Drakkith you are saying that we cannot know what we are in motion without an object with appears stationary to reference from.

But let's say our entire galaxy were in motion, which it probably is. And i don't mean the stars inside it are moving, this is obvious, I mean the galaxy as a unit were in motion.

Lets say we had nothing around us to tell if our galaxy is moving (I understand even if we did, we could not tell if we were stationary and the other object were moving or if we were moving, according to einstein) in a particular direction.

if we were to launch a clock in every direction away from the earth, would the clock which was launched in the opposite direction of our momentum experience time contraction ( I am using this as the opposite of time dilation. I mean time speeds at a faster rate if it is contracted, compared to our control clock on earth)?

Could we not figure out if we are in motion this way, without having even a second object to compare to, as long as we had these clocks to launch away?

I am assuming also that if we were in motion the clock that was launched in the direction we were traveling would not cover the same distance as the clock which was launched away from our direction of travel and we could determine our direction of travel this way

 

[questionator89]

What? The Earth cannot be at rest with the Sun, we are orbiting it. Do you understand what "at rest" means?

Drakkith I don't wan to seem unnappreciative because I totally am appreciative and want you to continue responding.
But maybe read a bit slower.
I said that the sun is also at rest in respect to the earth. which is orbiting the sun and moving.

I doubt there is any part of space which is not subject to gravitational fields. If the strength of the field was known could it be accounted for?

The only reason I bring up the fact that the clock would not be in an inertial frame is because you seem to have drawn some very incorrect conclusions from this premise. Honestly, you're better off just sticking to simple scenarios and not thinking about orbiting objects. It just gets complicated.[/QUOTE]

 

[Drakkith]

Again, i want to ask... So Drakkith you are saying that we cannot know what we are in motion without an object with appears stationary to reference from.

If you have nothing to measure against, then no. You cannot know you are in motion. How would you know?

But let's say our entire galaxy were in motion, which it probably is. And i don't mean the stars inside it are moving, this is obvious, I mean the galaxy as a unit were in motion.

Lets say we had nothing around us to tell if our galaxy is moving (I understand even if we did, we could not tell if we were stationary and the other object were moving or if we were moving, according to einstein) in a particular direction.

if we were to launch a clock in every direction away from the earth, would the clock which was launched in the opposite direction of our momentum experience time contraction ( I am using this as the opposite of time dilation. I mean time speeds at a faster rate if it is contracted, compared to our control clock on earth)?

Could we not figure out if we are in motion this way, without having even a second object to compare to, as long as we had these clocks to launch away?

Nope. Every clock will read identical time dilation from the Earth's frame. Without another object to compare ourselves to, we cannot say we are even in motion. What's changed position? We have no change in position over a change in time. We have only ourselves.

I am assuming also that if we were in motion the clock that was launched in the direction we were traveling would not cover the same distance as the clock which was launched away from our direction of travel and we could determine our direction of travel this way

In a simplified situation that ignores gravity, our orbit, etc, then we can say that every clock will be traveling at identical speeds and will travel the same distance in the same amount of time. So, no. There is no absolute motion through space, which is apparently what you are thinking.

 

[Dale]

questionator89, please don't hijack threads.

Also, please read the "rest frame of a photon" FAQ here:
https://www.physicsforums.com/forumdisplay.php?f=210