Is time dilation just a problem with our clocks?

[Edriven]

[Mentor's note: This thread was split off from https://www.physicsforums.com/threa...hift-for-a-static-black-hole-comments.835277/ as clarifying misunderstandings about time in general is off-topic in a thread about the specifics of time dilation around a black hole]

Loved the post, but is respectfully disagree with use of time dilation. Doesn't gravity affect light and matter? Is it not having an affect on our clock? Clock was designed to work on Earths surface. A change in function of this machine is only a loss of calibration to a different environment. Thus this time piece can work correctly in a stable environment, if it is recalibrated to that environment. So it would be closer to the truth if you said time dilation is only a relationship of the rest of our universe using Earths time. But time is a constant and can't be bent or altered.

 

[Edriven]

In addition. I think of it like this. Light traveling from a distant star can be used as a historical record of time. Much like archeologists date objects based on depth of dirt. But no one is saying we can bend the dirt-time continuum

 

[PeterDonis]

Clock was designed to work on Earths surface. A change in function of this machine is only a loss of calibration to a different environment.

This is not correct--at least, not for the clocks we use for making time measurements in physics experiments. Yes, a pendulum clock won't work well in space, but the solution for that is not to use pendulum clocks. Clocks based on crystal oscillators, such as an ordinary quartz watch, work just fine out in space. You don't have to "recalibrate" them.

You appear to be misunderstanding what "time dilation" is. It's not something you observe happening to yourself. To you, a clock you carry with you always appears to tick normally. But someone else observing you from a distance, who is moving relative to you, or who is in a region of different gravitational potential, would see your clock ticking differently.

 

[Edriven]

This is not correct--at least, not for the clocks we use for making time measurements in physics experiments. Yes, a pendulum clock won't work well in space, but the solution for that is not to use pendulum clocks. Clocks based on crystal oscillators, such as an ordinary quartz watch, work just fine out in space. You don't have to "recalibrate" them.

You appear to be misunderstanding what "time dilation" is. It's not something you observe happening to yourself. To you, a clock you carry with you always appears to tick normally. But someone else observing you from a distance, who is moving relative to you, or who is in a region of different gravitational potential, would see your clock ticking differently.

Gravity affects all matter my friend. The atomic clock is the most accurate clock avaliable. And it is still affected. Gps satellites must constantly be calibrated back to Earth time.
The astronaut that has spend the most time in space, over 2 years. Only lost .0007 of a second of time. (From memory so may not be 100%. But pretty close)! When he got back to Earth it would not matter to his ordinary clock. That's why ur using regular clocks. Because u can't tell unless u have a very accurate time piece.
Look up experiments of time dilation. It's concept is total right but it is misunderstood and misused.

 

[SlowThinker]

Gravity affects all matter my friend.

All kinds of matter and energy are affected in the same way. So we say that the time itself is affected.
If you are trying to deny the existence of gravitational time dilation, this is not the place to do it.

 

[PeterDonis]

Gravity affects all matter my friend.

Yes, we all agree on that.

The atomic clock is the most accurate clock avaliable.

Yes, we agree on that too.

And it is still affected. Gps satellites must constantly be calibrated back to Earth time.

Yes, because we need them to keep a time that is different from their "natural" time, the time they would keep if they weren't recalibrated. If you were riding along on a GPS satellite, and had an atomic clock to keep time, that clock would be keeping the "natural" time of the satellite, and the recalibrations back to Earth time would look to you like they were throwing the clock off, not correcting it.

Look up experiments of time dilation. It's concept is total right but it is misunderstood and misused.

Nobody here is denying that time dilation exists. But if you think it's being "misused", you're going to have to explain in detail why you think that, and give references.

 

[Boing3000]

But time is a constant and can't be bent or altered.

We are saying the exact same thing. The local "proper" time cannot change. How will you prove it change anyway ? (Because all local clock would change the same way)
That's the relationship (relatively to other frame of reference) of coordinate time that change.

 

[Edriven]

All kinds of matter and energy are affected in the same way. So we say that the time itself is affected.
If you are trying to deny the existence of gravitational time dilation, this is not the place to do it.

I'm not saying that gravitonal time is false. I'm saying it is misused. Time doesn't wrap, change, speed up, slow down etc. only the way that it is measured changes. So basically the clock changes. Not actual time.

 

[Nugatory]

I'm not saying that gravitonal time is false. I'm saying it is misused. Time doesn't wrap, change, speed up, slow down etc.

The "clocks" of relativity are any time-dependent process: the graying of my hair, sand falling through an hourglass, the decay of radioactive atoms, the decay of unrefrigerated meat, the motion of the Earth around the sun, the height of the tree in my front yard... Google for "Time is what a clock measures" to see the importance of this insight from Einstein.

So basically the clock changes. Not actual time.

How do you explain the twin "paradox" (http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html) then? Basically two identical twins by definition the same age shake hands; then take different journeys; then reunite to shake hands again. At the reunion, one of the twins has experienced less time and is physically less aged than the other. It's really hard to see how the difference in aging can be attributed to anything except having lived through different amounts of time between handshakes.

(Note: It's called the twin "paradox" because it's often presented as a paradox in elementary classes as a teaching tool, but in fact it's not a paradox - the correct and non-paradoxical resolution has been understood since the birth of relativity).

 

[PeterDonis]

basically the clock changes. Not actual time.

How would you measure "actual time" in order to distinguish the clock changing from "actual time" changing?

 

[Edriven]

How would you measure "actual time" in order to distinguish the clock changing from "actual time" changing?

Let's say we have a clock that had two sensor plates and light is bouncing back and forth. For simplicity, we will say every strike on a plate is one Earth second. To get Earth's time, we must put these plates at a certain distance apart, in accordance to Earth's environment. Therefore we are calibrating it our givin situation. When we change gravity or speed we simply move the plates apart to account for the effects of gravity and speed. Now we have calibrated it to that environment.
Another analogy is the pulsing of light from celestial objects. If Earth telescope looked at a pulsing object in space, would a telescope in space not observe the same pulse at the same rate? (same distance from pulse).

 

[Edriven]

How would you measure "actual time" in order to distinguish the clock changing from "actual time" changing?

I'm not trying to argue or be rude. I hope everyone understands that. I am merely saying that our time measuring devices ARE affected by gravity and movement based on laws, simply because gravity affects matter and light. Can we all agree on that? Therefore I'm saying the mechanism is affected. The person with this clock will see no difference because this is his only way to count time, thus his clock is relative to him. But if he knew a pulsing object, in space, had a certain rate, then he could compare this to his clock and see the loss of calibration.

 

[SlowThinker]

I am merely saying that our time measuring devices ARE affected by gravity and movement based on laws

But how do you explain that all kinds of clock, electromagnetic, gravitational or nuclear, get affected in exactly the same way? Isn't it simpler to say that the time itself is affected?
Anyway, what's the difference? Everything just happens slower in both cases.

 

[Dale]

Therefore I'm saying the mechanism is affected.

The problem is that you are saying more than that. You are not only saying that the mechanism is affected but you are also saying that there is some "actual time" which is not affected. Peter asked you to justify that specific claim by demonstrating how to measure this purported "actual time", which you avoided answering.

 

[Edriven]

The problem is that you are saying more than that. You are not only saying that the mechanism is affected but you are also saying that there is some "actual time" which is not affected. Peter asked you to justify that specific claim by demonstrating how to measure this purported "actual time", which you avoided answering.

I'm sorry. If I sound stubborn. I'm trying to respond to a lot of different posts here. I posted a response to this in another post. I understand it as, a person in space traveling with small gravity will have his clock slow down compared to a persons clock on earth. So when looking out the window he sees the same pulse, from another object in space. Would this pulse slow down for both observers? If so why? Also why does a clock going in a separate direction speed up vs slow down?

 

[Edriven]

But how do you explain that all kinds of clock, electromagnetic, gravitational or nuclear, get affected in exactly the same way? Isn't it simpler to say that the time itself is affected?
Anyway, what's the difference? Everything just happens slower in both cases.

They are all calibrated to same standard and all have matter.

 

[SlowThinker]

They are all calibrated to same standard and all have matter.

My questions stay the same.

 

[Edriven]

My questions stay the same.

According to this, a person can go into space and not age or age very slowly?

 

[Edriven]

My questions stay the same.

The difference would be huge. Would it have an affect on aging or just the clock? That is what I'm trying to determine?

 

[SlowThinker]

According to this, a person can go into space and not age or age very slowly?

The contrary. In the space you age fastest. On the Earth you age at about 99.99999993% of that speed. Close to the horizon of a black hole, you can age at 1% speed or even slower.

 

[Orodruin]

According to this, a person can go into space and not age or age very slowly?

No. The gravitational time dilation at the Earth's surface is miniscule compared to a faraway observer. Also, the effect is in the other direction.

 

[Edriven]

The contrary. In the space you age fastest. On the Earth you age at about 99.99999993% of that speed. Close to the horizon of a black hole, you can age at 1% speed or even slower.
https://en.m.wikipedia.org/wiki/Hafele–Keating_experiment

Thank you. Can you please explain why the clocks on the planes change according to their direction of travel?

 

[SlowThinker]

https://en.m.wikipedia.org/wiki/Hafele–Keating_experiment
Thank you. Can you please explain why the clocks on the planes change according to their direction of travel?

That is a different effect, known as special relativity.

 

[PeterDonis]

In the space you age fastest.

I assume you mean, a person at rest "at infinity" (meaning, far enough away from all gravitating bodies that their gravity is negligible) ages fastest. "In space" is much more general; astronauts in the Space Shuttle in low Earth orbit aged slower than people at rest on the Earth's surface (because the slowing down due to their orbital velocity was more than the speeding up due to their higher altitude).

 

[PeterDonis]

Can you please explain why the clocks on the planes change according to their direction of travel?

AFAIK most GR textbooks have at least some discussion of the Hafele-Keating experiment. The easiest way to analyze it is to use an "inertial" frame in which the center of the Earth is at rest. In this frame, a clock at rest on the (rotating) Earth's surface (like the reference clock in the experiment) is moving at about 450 m/s. The clock on the eastbound plane was moving at about 750 m/s (about 300 m/s relative to the surface of the rotating Earth, and in the same direction), and the clock on the westbound plane was moving at about 150 m/s (about 300 m/s relative to the surface of the rotating Earth, but in the opposite direction). The different speeds of the two clocks is why their observed rates were different (they were both at the same altitude, about 10,000 meters above the Earth's surface, so they both had about the same difference in gravitational time dilation compared to the reference clock).

 

[Edriven]

AFAIK most GR textbooks have at least some discussion of the Hafele-Keating experiment. The easiest way to analyze it is to use an "inertial" frame in which the center of the Earth is at rest. In this frame, a clock at rest on the (rotating) Earth's surface (like the reference clock in the experiment) is moving at about 450 m/s. The clock on the eastbound plane was moving at about 750 m/s (about 300 m/s relative to the surface of the rotating Earth, and in the same direction), and the clock on the westbound plane was moving at about 150 m/s (about 300 m/s relative to the surface of the rotating Earth, but in the opposite direction). The different speeds of the two clocks is why their observed rates were different (they were both at the same altitude, about 10,000 meters above the Earth's surface, so they both had about the same difference in gravitational time dilation compared to the reference clock).

Thank you for they detailed explanation. If an observer on Earth and an observer in orbit,around the earth, could see the same pulsar, what would be the outcome when compared to their clocks?

 

[Orodruin]

Thank you for they detailed explanation. If an observer on Earth and an observer in orbit,around the earth, could see the same pulsar, what would be the outcome when compared to their clocks?

This depends on the orbit. The time dilation relative to the Earth surface experienced in orbit is a combination of gravitational time dilation and time dilation due to movement.

 

[PeterDonis]

If an observer on Earth and an observer in orbit,around the earth, could see the same pulsar, what would be the outcome when compared to their clocks?

There are actually two questions here, and it's important to distinguish them.

Question #1: Consider an instant at which the Earthbound observer E and the orbiting observer O both lie along the radial line of sight to the pulsar, so they are both seeing the same portion of the beam of light signals from the pulsar. What frequency of pulses will each one observe?

Question #2: Suppose that the Earth is transparent to pulsar signals, so both observers, E and O, can count pulses from the pulsar while O goes around one complete orbit. How many pulses will each one count?

The answer to question #1, as Orodruin points out, depends on the orbit of O. If O is in low Earth orbit, his clock rate will be slower than E's clock rate, so, since frequency goes as the inverse of clock rate, O will observe a faster frequency of pulses from the pulsar than E will. If O is in a high orbit, such as an orbit at the altitude of the GPS satellites, his clock rate will be faster than E's, so he will observe a slower frequency of pulses from the pulsar than E will.

The answer to question #2, however, is independent of all that; the answer is that, in one complete orbital period of O, both O and E must observe the same number of pulses coming in from the pulsar. They will disagree on how much clock time the orbit took, so they will disagree on the frequency of the pulses, but they will agree on the total number of pulses in one orbital period of O.

 

[Edriven]

There are actually two questions here, and it's important to distinguish them.

Question #1: Consider an instant at which the Earthbound observer E and the orbiting observer O both lie along the radial line of sight to the pulsar, so they are both seeing the same portion of the beam of light signals from the pulsar. What frequency of pulses will each one observe?

Question #2: Suppose that the Earth is transparent to pulsar signals, so both observers, E and O, can count pulses from the pulsar while O goes around one complete orbit. How many pulses will each one count?

The answer to question #1, as Orodruin points out, depends on the orbit of O. If O is in low Earth orbit, his clock rate will be slower than E's clock rate, so, since frequency goes as the inverse of clock rate, O will observe a faster frequency of pulses from the pulsar than E will. If O is in a high orbit, such as an orbit at the altitude of the GPS satellites, his clock rate will be faster than E's, so he will observe a slower frequency of pulses from the pulsar than E will.

The answer to question #2, however, is independent of all that; the answer is that, in one complete orbital period of O, both O and E must observe the same number of pulses coming in from the pulsar. They will disagree on how much clock time the orbit took, so they will disagree on the frequency of the pulses, but they will agree on the total number of pulses in one orbital period of O.

Thank you again, for your details and time. This pulsar to me is a "God clock". A time piece, free of restraints of gravity and material limits. Could this pulsar not be used, as a universal time piece? It seems more consistent than our man made clocks.

 

[Nugatory]

A time piece, free of restraints of gravity and material limits.

Careful... what we're counting here is not pulses of the pulsar, we're counting the the number of times that a pulse wavefront passes through in the general neighborhood of the earth. You could call the amount of time that ten flashes pass by some unit of time; and you could notice that during that time twenty flashes from some other pulsar pass through the neighborhood of the earth... But there's no reason to expect that twenty:ten ratio to hold anywhere else in the universe, nor even if the Earth's orbital velocity were different. So which pulsar is to be "god's clock"? They can't both be, because they only agree in one place.

The behavior PeterDonis described for the pulsar (same number of flashes received in one orbital period of O) could just as easily be achieved by setting a strobe light up on the surface of the earth.

 

[Edriven]

Careful... what we're counting here is not pulses of the pulsar, we're counting the the number of times that a pulse wavefront passes through in the general neighborhood of the earth. You could call the amount of time that ten flashes pass by some unit of time; and you could notice that during that time twenty flashes from some other pulsar pass through the neighborhood of the earth... But there's no reason to expect that twenty:ten ratio to hold anywhere else in the universe, nor even if the Earth's orbital velocity were different. So which pulsar is to be "god's clock"? They can't both be, because they only agree in one place.

The behavior PeterDonis described for the pulsar (same number of flashes received in one orbital period of O) could just as easily be achieved by setting a strobe light up on the surface of the earth.

Thank you. I was actually thinking of the moon because of its rotation. So let's just theorize for a second that we did this. Both observers (earth and space) could see the strobe. Would the flashes not act like a clock by counting them? Would they also not count the same number of flashes by the light given off?

 

[PeterDonis]

This pulsar to me is a "God clock". A time piece, free of restraints of gravity and material limits.

Didn't you say in an earlier post that gravity affects everything, since everything is made of matter and energy? Why do you think a pulsar would be any different?

 

[PeterDonis]

Would the flashes not act like a clock by counting them?

They can serve as a sort of "clock", yes; but there is no guarantee that each "tick" of the clock (i.e., each pair of successive flashes) represents the same amount of time. It depends on the motion of the source of the flashes, the motion of the receiver, the position of each in a gravity well, etc.

 

[Edriven]

They can serve as a sort of "clock", yes; but there is no guarantee that each "tick" of the clock (i.e., each pair of successive flashes) represents the same amount of time. It depends on the motion of the source of the flashes, the motion of the receiver, the position of each in a gravity well, etc.

The only thing that matters,in this instance, is that the strobe can be seen by the earthling and the space traveler. Thus,they would be witnessing the same event at the same time. Gravity would only take hold if we had enough to create gravitational lensing. I think their clocks would still be running at different speeds. Would this example not prove that time dilation only effects clocks and not time itself?

 

[PeterDonis]

they would be witnessing the same event at the same time.

No, they wouldn't. They aren't at the same spatial location. They are not at rest relative to each other. Both of these things will affect their relative clock rates, so their clocks won't show the same elapsed time between pulses. They will agree on invariants, like how many pulses are received during one orbit of the space traveler, because the definition of "one orbit" is the same for both of them. But they won't agree on how much clock time elapses during one orbit.

Gravity would only take hold if we had enough to create gravitational lensing.

Incorrect. Gravity affects their relative clock rates because they are at different altitudes.

I think there clocks would still be running at different speeds.

Yes, indeed. See above.

Would this example not prove that time dilation only effects clocks and not time itself?

No, because "time itself" independently of clocks is meaningless. I asked you in a previous post how you would measure "time itself" without using a clock; you never answered.