Time Dilation Probes: Exploring the Possibilities

[Engineer_pleb]

TL;DR Summary

Defining time dilation zones in order to find the slowest moving region in the universe

Firstly, I am a Mechanical engineer working in the aerospace industry and I know very little compared to the collective community here and my formal education had to do with practical and basic stuff, so apologies if I’m overlooking a basic principle or something.

my idea: what if we launched a bunch of probes at specific velocities into space and record the amount of time it take each probe to travel a certain distance, then finding how much time dilation that probe experienced... using the data from a bunch of these probes going in various directions, create a 3 dimensional data field, then define some layer lines based on how much time dilation each probe experienced compared to that of Earth assuming Earth is zero/control. I suspect if you sent enough probes far enough out (I don’t know how far out, a few km? thousands of light years?) I’d suspect you’d be able to layer the time dilation data as a series of spheres where time dilation increases as the probes travel with greater velocity towards the outer layers. If I’m right, then the center of the sphere would have zero time dilation and we could in theory launch a probe at the exact velocity dictated by that data at the exact angle to negate the inertia the probe had while on earth, and that probe could be said to have absolute zero velocity...?

now I’m really stretching my luck with this statement, but if we found an absolute zero speed, then we could just used data we have of the inertia of other galaxies and track it all back with probably a lot of error back to some converging area, the center of the universe.

This might be physics vomit but I’m very curious.

 

[mfb]

There is no absolute velocity and time dilation from motion is symmetric. We will see the clocks on the spacecraft run slower, the spacecraft will see the clocks on Earth run slower by the same amount.

There is also no "outer layer", whatever that is supposed to mean. All points in the universe are equal on a large scale. The universe doesn't have a center or an edge.

 

[Engineer_pleb]

correct me if I’m wrong but if you travel faster, you will experience time slower. I know each reality is relative, but the reason I thought of this is because we have to adjust satellites For time dilation, so i wasn’t sure if you linearly sent probes in multiple directions, if one probe may be experiencing a faster time than another probe or if it’s all the same and time dilation has no correlation with your position in the universe.

 

[PeterDonis]

if you travel faster, you will experience time slower

No, this is wrong. You experience time the same--one second per second.

If you and I follow different paths through spacetime, and then we compare our elapsed times after we meet up again, our elapsed times might be different, yes. But the rule for determining which one of our elapsed times will be shorter is not "which one is moving", because "moving" has no absolute meaning. You have to actually look at the geometry--at the geometry of spacetime and the specific paths you and I follow through that geometry.

I know each reality is relative

No, "reality" is not relative. "Reality" is the things that are invariant--that don't depend on how you choose your coordinates. "Time dilation" is not "reality" in that sense. But differential aging--different elapsed times for people following different paths through spacetime--is "reality". It just doesn't work the way you are thinking; see above.

the reason I thought of this is because we have to adjust satellites For time dilation

No, we have to adjust them for differential aging--the fact that, for example, the elapsed time on a GPS satellite's clock, between one time it passes directly over some reference point (such as the U. S. Naval Observatory, where, IIRC, the master reference atomic clocks for the GPS system are located) and the next, is longer than the elapsed time on the clock on the ground. So we have to correct for that because we want the reference time for GPS to be the time on the ground clock.

if you linearly sent probes in multiple directions, if one probe may be experiencing a faster time than another probe

Whether there was differential aging between the probes would depend on the specific geometry of the spacetime region where you sent the probes.

or if it’s all the same and time dilation has no correlation with your position in the universe.

Differential aging does depend on spacetime geometry, so, for example, if we put satellites in orbit about the Moon with the same altitude as GPS satellites orbit about the Earth, the differential aging between them and clocks on the Moon's surface would not be the same as the differential aging between GPS satellite clocks and Earth ground clocks.

 

[Engineer_pleb]

This is more wild than i imagined initially, but I think I understand a little more now and why my idea wouldn’t work. I think I was trying to force the idea of absolutism upon a strictly relativistic system. I really appreciate the in depth explanations it helped a lot.

when you refer to differing spacetime geometries, are we talking about how gravity warps the geometry ?

 

[Ibix]

I think I was trying to force the idea of absolutism upon a strictly relativistic system.

Basically, yes. Although be wary of going too far the other way and concluding "everything is relative". Velocity certainly is, and time dilation depends on the square of velocity, so that's all relative. But many things (notably, instrument readings) can be expressed in coordinate-independent ways. The theory wouldn't be much use if it couldn't predict the results of some experiment, even if it does provide multiple routes to get there.

when you refer to differing spacetime geometries, are we talking about how gravity warps the geometry ?

Gravity is spacetime curvature. Peter is simply noting that if you are in a different gravitational field you may well get different results from the same experiment. This is obviously true (drop a hammer here and do it on the moon - measure the fall time). What's relevant here is that comparing clock tick rates can give different results in different gravitational fields.

 

[Orodruin]

when you refer to differing spacetime geometries, are we talking about how gravity warps the geometry ?

Gravity does not warp the geometry, gravity is the curvature of spacetime.

Spacetime ultimately is described as a geometrical object that differs in many regards to the normal geometry of Euclidean space that we are all quite familiar with. However, it is also similar in many regards. You do not need to go into GR in order to encounter the geometry of spacetime, it is present in SR too, but with a flat geometry rather than a curved one (this does not prevent there being geometrical effects, see my Insight https://www.physicsforums.com/insights/geometrical-view-time-dilation-twin-paradox/).

 

[1977ub]

I wonder if one could try to remove the confounding influence of velocity between differing frames. A probe can be edged toward a gravitating body, and at each step, held so that it is a constant distance, then the probe definitely reports slower clock speeds the closer it gets. This could be done throughout a region where distances are agreed to be mainly static between observers.

 

[Ibix]

I wonder if one could try to remove the confounding influence of velocity between differing frames.

That's not "frames" really, but you can certainly do this kind of experiment. I believe these days atomic clocks are precise enough to measure the difference in tick rates between clocks on and under a desk. However, it's only possible to separate tick rate comparisons into a component due to velocity and a component due to height in a class of spacetimes called "stationary" spacetimes. The Earth's gravitational field is a very decent approximation to stationary, but once you're looking at the whole solar system and beyond it gets harder and harder to pretend.

 

[mfb]

I believe these days atomic clocks are precise enough to measure the difference in tick rates between clocks on and under a desk.

Time dilation with 30 cm height difference.
The clocks are so good you have to specify where in the clock the time reference is.

 

[PAllen]

Time dilation with 30 cm height difference.
The clocks are so good you have to specify where in the clock the time reference is.

Shame on NIST for its description of gravitational time dilation in terms off force rather than potential. New Scientist, I'd expect such, but NIST!??

 

[vanhees71]

Well, it's more difficult to write a correct popular-science article than a scientific paper. I'm pretty sure NIST physicists know that in relativity there are no forces but only local interactions in the sense of field theory, but to write in a way to be understandable by the public they use the more common experience of non-relativistic forces.

 

[PAllen]

Well, it's more difficult to write a correct popular-science article than a scientific paper. I'm pretty sure NIST physicists know that in relativity there are no forces but only local interactions in the sense of field theory, but to write in a way to be understandable by the public they use the more common experience of non-relativistic forces.

The issue is that even looked at in Newtonian fashion, time dilation is proportional to potential difference not force. The maximum time dilation may be where there is no gravitational force, e.g. center of a planet. This is perfectly explainable in terms of Newtonian potential, but not Newtonian force. We get much confusion here from people thinking in terms of force.

 

[vanhees71]

?

In Newtonian physics there's no gravitational time dilation at all in accordance with Newton's notion of absolute time (and space), or do you mean the non-relativistic approximation of the metric, where only the Newtonian potential of the Newtonian gravitational force enters (and in Newton's physics gravity is described as an instantaneously acting force though already Newton himself had his doubts about the concept of an instantaneous action at a distance)?

 

[PAllen]

?

In Newtonian physics there's no gravitational time dilation at all in accordance with Newton's notion of absolute time (and space), or do you mean the non-relativistic approximation of the metric, where only the Newtonian potential of the Newtonian gravitational force enters (and in Newton's physics gravity is described as an instantaneously acting force though already Newton himself had his doubts about the concept of an instantaneous action at a distance)?

Of course that’s what I mean and what I said. You introduce that time dilation is proportional to Newtonian potential difference, and you get over 6 significant figures accuracy anywhere around and in a planet like earth. The key point is simply that if you want to build on beginner intuitions, you want to use the concept of potential energy difference not force, when talking about gravitational time dilation.