This discussion centers on the concept of time dilation, particularly in relation to gravitational effects on clocks. Participants clarify that while clocks, such as atomic clocks, are indeed affected by gravity, the notion that time itself can be altered is a misunderstanding. Time dilation is a relative phenomenon observed from different frames of reference, and accurate timekeeping devices like quartz watches function correctly in various environments without needing recalibration. The conversation emphasizes that while the measurement of time can change, the fundamental nature of time remains constant.
PREREQUISITESPhysicists, students of relativity, and anyone interested in the implications of time dilation on modern technology such as GPS systems.
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?Nugatory said: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 said:This pulsar to me is a "God clock". A time piece, free of restraints of gravity and material limits.
Edriven said:Would the flashes not act like a clock by counting them?
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 said: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 said:they would be witnessing the same event at the same time.
Edriven said:Gravity would only take hold if we had enough to create gravitational lensing.
Edriven said:I think there clocks would still be running at different speeds.
Edriven said:Would this example not prove that time dilation only effects clocks and not time itself?
I'm sorry. I don't want to measure time without a clock. I just want to use a different clock. One free of gravity and speed, if there is such a thing. We both know enironment would determine this.PeterDonis said: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.
Can we work on one thing at a time, please? If we said they were both traveling at same rate where them gravity would only be the varing factor. Would the pulses change? Then, if we have two observers on Earth going at different speeds, speed would be the variable. Would the pulses change here? I think in both cases the moon would appear stationary. Does that sound right?Incorrect. Gravity affects their relative clock rates because they are at different altitudes.
Yes, indeed. See above.
Yes I agree. It affects their relative clocks. The gravity from the moon to spacecraft is constant for both parties. The only difference is light traveling from altitude to surface. Would there be much of a change here?
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.
Edriven said:I just want to use a different clock. One free of gravity and speed, if there is such a thing.
Yes sir you are absolutely right.PeterDonis said:There isn't. As you yourself pointed out in an earlier post, gravity affects everything. "Speed" also affects everything, in the sense that there is no such thing as absolute rest.
It is not that you sound stubborn; you sound evasive. You are still avoiding the question. Please tell how you propose to measure this "actual time" which you claim exists and does not change.Edriven said: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?
Man made atomic clocks are FAR more stable than pulsars. Furthermore, pulsars would be just as affected by gravity and speed as any other clock. If that is your measure of time then time still dilates.Edriven said: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.
Yes, thank you. I was using the pulsar as a natural example. Something that maybe Einstein could of referred too. My true choice would be to place a strobe omitter on the moon. This placement would allow both, the Earth observer and a spacecraft to compare the flashes of light to their clocks. It would take gravity out of the equation and put the clock on an object that doesn't seem to move when observed, but visible to both parties.DaleSpam said:Man made atomic clocks are FAR more stable than pulsars. Furthermore, pulsars would be just as affected by gravity and speed as any other clock. If that is your measure of time then time still dilates.
Edriven said:Yes, thank you. I was using the pulsar as a natural example. Something that maybe Einstein could of referred too. My true choice would be to place a strobe omitter on the moon. This placement would allow both, the Earth observer and a spacecraft to compare the flashes of light to their clocks. It would take gravity out of the equation and put the clock on an object that doesn't seem to move when observed, but visible to both parties.
Edriven said:I'm sorry. I don't want to measure time without a clock. I just want to use a different clock. One free of gravity and speed, if there is such a thing. We both know enironment would determine this.
I'm here not to doubt it, but to understand it. Thank you.stevendaryl said:You seem to have a concept of Special and General Relativity that I think is different from the standard view. That doesn't mean it's wrong, but I think it would be worth your while to understand the standard view before launching into an unorthodox interpretation.
In SR or GR, you can have two clocks that start together, take different paths through time and space, and when they get back together they show different amounts of elapsed time. You seem to have in mind an "environmental" interpretation of this: The forces that act on the clocks slow them down by different amounts, and that explains the difference. You think that if there were such a thing as a "perfect" clock, then its elapsed time would be unaffected by gravity or speed. That is NOT correct, according to the standard view. (Once again, I'm saying that the standard view is the only possible way of looking at it.)
The standard view of SR and GR is that clocks don't measure time, but they measure PROPER time, and proper time is a geometric quantity. Here's an analogy: Two cars both start on a road trip from New York City to Seattle. One car takes Interstate 90 all the way across the country. The other car goes south to Georgia, then west to California, then north to Seattle. When the two cars get back together in Seattle, they compare their odometer readings. One car's odometer shows that the trip was 3000 miles. The other car's odometer shows that the trip was 4500 miles. How is that possible? They both started in New York and ended in Seattle?
One interpretation of the difference in odometer readings is an "environmental" interpretation. For some reason, going south and then west and then north caused that car's odometer reading to "run fast", so that it showed more miles. The other interpretation is geometric: Both cars accurately measured the length of their trips, but trip length is a path-dependent quantity.
The geometric interpretation of SR and GR says that clocks accurately measure a kind of "path length" through spacetime, which is called proper time. This quantity is path-dependent, it isn't just a function of where (in spacetime) you start and where you end up.
Edriven said:I'm here not to doubt it, but to understand it. Thank you.
But a long time and very fast speed would have to be required to make any real difference right?stevendaryl said:Well, the geometric view is that there is no wrong, or inaccurate, about the clocks used to measure time dilation. In the same way that there can be two different ways to go from New York City to Seattle, and they have different path lengths, there can be two different ways to go from the point in spacetime "Earth on June 1, 2015" to the point "Earth on June 1, 2025", and those two different paths can have different proper times, which is like a path length.
You certainly could do that, but a strobe emitter would be just as susceptible to gravitational time dilation and kinematical time dilation as any other clock. If the goal is to measure a "actual time" immune to such effects, then this wouldn't do it. All it would do is provide a specific non-actual time to use as a standardized reference. There may certainly be some benefit to establishing such a conventional reference, the GPS system does that also, but it is hardly the measurement of "actual time".Edriven said:My true choice would be to place a strobe omitter on the moon. This placement would allow both, the Earth observer and a spacecraft to compare the flashes of light to their clocks.
Thank you. I have gotten this response from others. What an amazing science.DaleSpam said:You certainly could do that, but a strobe emitter would be just as susceptible to gravitational time dilation and kinematical time dilation as any other clock. If the goal is to measure a "actual time" immune to such effects, then this wouldn't do it. All it would do is provide a specific non-actual time to use as a standardized reference. There may certainly be some benefit to establishing such a conventional reference, the GPS system does that also, but it is hardly the measurement of "actual time".
Edriven said:Thank you. I have gotten this response from others. What an amazing science.
Thank you. This entire group has helped me a lot.Nugatory said:Your best bet for understanding this is to defer gravitational considerations for now and instead focus on how time dilation works with ordinary boring constant-speed straight-line motion. Get clear in your mind how it can be that if someone is moving relative to you, then you will (correctly) find their clocks are running slow relative to yours - but they, working from the equally valid standpoint that they're at rest and you're moving relative to them - will (correctly) find that your clock is running slow relative to theirs.
Starting here has several advantages:
- It's much easier to avoid the pitfall of thinking that time dilation is something that happens to the time-dilated observer; you don't expect to be much affected by the fact that some observer in some far distant corner of the cosmos (or racing around the storage rings of the Large Hadron Collider at CERN) is moving at 99% of the speed of light relative to you.
- You don't have to unlearn the idea that gravity is a force before you can even get started.
- The math is much less demanding. There are respectable and acceptably rigorous ways of approaching the constant-speed straight-line no-gravity problem without even using any calculus... but to involve gravity at any but the most superficial level requires several years of serious college-level math.
No.Edriven said: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.
Peter answered "yes" to all of these, but because of the way the answers were split, it implied something to me that is not true, which was the reason for my previous post. In the sense that local measurements/calculations can detect/explain the effect of gravity on a pendulum clock, the claim that the atomic clock is also affected by gravity is false, not true. The atomic clock is "affected" by time dilation, which is measured between frames. The pendulum clock is affected by gravitational acceleration, which can be measured locally. That's why I prefer answering "no" to the question of whether gravity affects clocks. It depends on what you are referring to and in the context of Relativity (the laws of the universe are the same in all inertial frames), I believe the answer should be "no" (for a good clock). It's time itself that is different between frames: the clock is just along for the ride.Edriven said: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.
russ_watters said:There is a well known equation for predicting the tick rate of a pendulum clock based on changes in gravitational acceleration. There is no such equation for a quartz clock, spring clock, atomic clock, motorized clock, radioactive decay clock, etc.
russ_watters said:The atomic clock is "affected" by time dilation, which is measured between frames. The pendulum clock is affected by gravitational acceleration, which can be measured locally
Agreed. So my point was that while we have/know a specific mechanism that causes a pendulum clock to vary vs an "ideal' clock, there are no known mechanisms for those other types of clocks that would explain-away time dilation (and in fact, if we could build a precise enough pendulum clock or generate a high enough speed or gravitational potential, it would still be noticed to be subject to time dilation as well).PeterDonis said:I think this can be phrased in a way that makes the difference even more evident. The well known equation for the tick rate of a pendulum clock expresses that tick rate in terms of...the tick rate of those other kinds of clocks. In other words, to use the concept of "tick rate" at all, we need to have the concept of an "ideal" clock, one whose tick rate is not affected by any environmental factors like changes in the gravitational field. When we say the tick rate of other clocks, like a pendulum clock, is affected by changes in the environment, we mean that we can see the change by comparing those other clocks to an ideal clock. But in order to make that comparison, we have to have an ideal clock--we have to have at least one kind of clock which we treat as not being affected by changes in the environment.
So, while I get what you mean, I just feel that to someone like the OP there may not be a clear enough difference between that and the previous passage. As long as we can make sure that they are clear that that "affected by gravity" means something different for the atomic clock than for the pendulum clock, I guess that would be ok. But I prefer not having a difference because I'm not sure in other, similar contexts we'd use that framing. Consider:But if we then take two such ideal clocks, and send them on different paths through spacetime between the same pair of events, they will, in general, register different elapsed times. That means that even ideal clocks are "affected by gravity" in the sense that their elapsed times depend on the paths they take through spacetime.
Exactly.Yes, this is a good way of describing the distinction between a non-ideal clock and an ideal clock. An ideal clock is only affected by the length of the path it takes through spacetime, which is a global property; a non-ideal clock is affected by other things, which are locally measurable properties.
Muons seem to qualify. They were subjected to accelerations of something like 10^18 g and still kept time as we would expect from ideal clocks in relativityPeterDonis said:t in order to make that comparison, we have to have an ideal clock--we have to have at least one kind of clock which we treat as not being affected by changes in the environment.
DaleSpam said:Muons seem to qualify.
Thank you, I will research this topic more.DaleSpam said:Muons seem to qualify. They were subjected to accelerations of something like 10^18 g and still kept time as we would expect from ideal clocks in relativity
OK, here is a reference to help get you started.Edriven said:Thank you, I will research this topic more.
There are a lot of factors involved but it seems plant life happens is not affected.DaleSpam said:OK, here is a reference to help get you started.
Bailey et al., “Measurements of relativistic time dilation for positive and negative muons in a circular orbit,” Nature 268 (July 28, 1977) pg 301.
That shows that plants grow differently and better under conditions of weightlessness. This effect is so large as to overwhelm (by many orders of magnitude) the relativistic effects that we've been discussing in this thread.Edriven said:There are a lot of factors involved but it seems plant life happens is not affected.
http://www.nasa.gov/vision/earth/technologies/aeroponic_plants.html