>a clock on satellite moves slower than a clock on earth, because the satellite is moving faster relative to earth

>a clock on satellite moves slower than a clock on earth, because the satellite is moving faster relative to earth
>but relative to the satellite, the earth very well might be moving faster, unless you're measuring it against a third object there's no way to tell whether the earth is moving or the satellite is
Explain how the clock on the satellite knows it's moving faster, rather than slower, IQfy. Is there not a universal aether which provides a constant against which motion is measured?

https://en.m.wikipedia.org/wiki/Einstein-aether_theory

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  1. 3 weeks ago
    Anonymous

    For a more concrete example:
    >two balls are floating in a black void
    >one ball floats away from the other on
    >with no background against which to measure the distance between the balls, both balls are accelerating in opposite directions at an equal rate
    If you're picturing a camera angle in your mind, and one ball is rolling off screen, that's not correct. You've just imagined a fixed frame of reference for this ball-universe. Instead imagine you're standing on one of the balls. The other ball grows smaller in the sky. Is your ball moving, or is the other ball?

    • 3 weeks ago
      Anonymous

      In these cases you measure the time to unequivocally establish the speeds of each object.

  2. 3 weeks ago
    Anonymous

    There are models of relativity that use space dilation rather than time dilation but proposing an actual aether is not really helpful.

    • 3 weeks ago
      Anonymous

      The Wikipedia page says it's either stars or black holes

    • 3 weeks ago
      Anonymous

      >proposing an actual aether is not really helpful
      It's extremely helpful. Just call it a field or something.

  3. 3 weeks ago
    Anonymous

    Satellite isn't moving away, it's orbiting and accelerating around gravity well that's objective motion. If you want to be banal about it, you can presume the satellite is stationary and earth is wildly accelerating and then apply the same measurements of the clocks, apply the rules of relativity and find the same adjustments necessary.

    • 3 weeks ago
      Anonymous

      What does this mean? What's the still object against which the other two objects' speed is measured? It's a literal fact that the satellite clock is slower, so how can you "assume the earth is moving faster" when it can't be?

      • 3 weeks ago
        Anonymous

        Motion is measured with respect to the observer. Someone sitting on the Earth sees the satellite moving fast, they would see it's clock tick slowly. The clock on the spacecraft isn't running slow from its perspective.
        Note this is a bad example because there is no symmetry here, one of the objects is accelerating which is not relative. There is a genuine ambiguity in the twin paradox, but using a satellite as an example unhelpful because you add acceleration and gravity.

        Any observer can measure the speed from their location. Different observers don't have to agree. Different observers also don't have to agree on time dilation either.

        • 3 weeks ago
          Anonymous

          Yep

        • 3 weeks ago
          Anonymous

          There isn't an ambiguity in the twin paradox. One twin returns to the other.

          • 3 weeks ago
            Anonymous

            More like Amsmalluity.

          • 3 weeks ago
            Anonymous

            Both can say the other returned, but one has to accelerate. It's not ambiguous if the full physics is considered, but it's called the paradox because it's not trivial.

          • 3 weeks ago
            Anonymous

            It is trivial. A straight path between two spacetime events always takes the most proper time and one twin did not take a straight path. It is not a paradox to anyone that has learned special relativity

          • 3 weeks ago
            Anonymous

            >one twin did not take a straight path
            wich one?

          • 3 weeks ago
            Anonymous

            The one that left and came back

        • 3 weeks ago
          Anonymous

          >Someone sitting on the Earth sees the satellite moving fast
          An orbit is a route/way/trace/path defined by the fact that all it's relative speeds sums up to zero.

          • 3 weeks ago
            Anonymous

            Only if you average the velocity in time, which is meaningless for doing relativity.

        • 3 weeks ago
          Anonymous

          OK, so you are of the opinion that an observer on the satellite would see the clock display literally a different number than an observer on the ground?

          The satellite is accelerated whereas the earth is approximately not on this scale. An accelerated worldline is curved in spacetime so this is an unambiguous concept which doesn't depend on choice of observers or frames (which is early 1900's language for spacetime coordinate systems, but for some reason the latter is never taught at the popsci level).

          So the extent to which a worldline is curved can be measured against some worldline which is not curved, so that which line is curved compared to which is visible?

          • 3 weeks ago
            Anonymous

            >OK, so you are of the opinion that an observer on the satellite would see the clock display literally a different number than an observer on the ground?
            The question doesn't really make sense, because it's missing information. When do they each look at the clock? There is no absolute way to syncronise that. And even ignoring relativity there is a delay due to the speed of light.
            The objective thing is that the person on the ground sees the satellite clock ticking slowly. That doesn't require synchronisation. The person on the satellite does not see their clock ticking slowly.
            Not the person talking about worldliness.

          • 3 weeks ago
            Anonymous

            Why doesn't the clock seem to move faster to the person on the ground, rather than slower? Why do GPS companies have to program their satellite clocks to correct in the direction of moving slower, rather than moving faster?

          • 3 weeks ago
            Anonymous

            Time dilation if moving clocks is one of the implications of the speed of light being constant for all observers.

          • 3 weeks ago
            Anonymous

            OK, so the speed of light is the fixed constant which serves as the "aether" against which relative velocity can be calculated. Doesn't this violate Lorentz Invariance?

            In these cases you measure the time to unequivocally establish the speeds of each object.

            I'm not asking how an observer can tell what's moving faster, I'm asking how the universe can "tell" what's moving faster. It's a fact that the satellite is moving faster, but that fact doesn't make sense unless you can answer the question "moving faster relative to what".

          • 3 weeks ago
            Anonymous

            >I'm not asking how an observer can tell what's moving faster, I'm asking how the universe can "tell" what's moving faster.
            Imagine being this moronic

          • 3 weeks ago
            Anonymous

            I asked:
            >if a faster object experiences slower time than a slower object, what is the faster object faster relative to?
            You said:
            >You look at which object is moving faster to tell which object is experiencing slower time
            YOU are moronic.

          • 3 weeks ago
            Anonymous

            Incorrect. I told you to measure the time, not the speed, moron.

          • 3 weeks ago
            OP

            >if a faster object experiences slower time than a slower object, what is the faster object faster relative to?
            To which you claim you replied:
            >The object which experiences slower time is the faster one
            Am I getting this right? Because that doesn't answer my question at all

          • 3 weeks ago
            Anonymous

            >OK, so the speed of light is the fixed constant which serves as the "aether" against which relative velocity can be calculated.
            No it does not do that. For one it's a speed not a velocity, it makes no sense. All observers measure the speed of light as the same. It tells you nothing about which things are moving because it's always the same.
            >I'm not asking how an observer can tell what's moving faster, I'm asking how the universe can "tell" what's moving faster.
            It doesn't. There is no absolute sense of motion. Different observers will see it differently and they will measure time dilation differently. They don't have to agree.
            >moving faster relative to what
            The only answer in relativity is the observers rest frame. That is where the clock is being viewed from so that's the relative velocity that matters.

          • 3 weeks ago
            Anonymous

            OK. Let's say you have an observer on a satellite observing a clock on earth, and an observer on earth observing a clock on the satellite. Would they BOTH see the clock their looking at as slower than their own clock?

          • 3 weeks ago
            Anonymous

            Say instead that there are two spacecraft passing each other in space. Neither is accelerating and there are no gravitational fields.
            Both see the clock in the other spacecraft running slow. Because it's moving with respect to them. They don't have to agree.

          • 3 weeks ago
            Anonymous

            >So the extent to which a worldline is curved can be measured against some worldline which is not curved, so that which line is curved compared to which is visible?

            There is a mathematical object in physics called the "measure" that lets you measure the length of a worldline between two events, and this length is the same thing as the proper time that elapsed. It doesn't depend on frame or coordinates. You don't actually need to compare two worldlines to calculate this length or proper time. I brought up "curved" worldlines because usually in examples like this that are similar to the twin paradox you are comparing one worldline that is approximately a geodesic ("uncurved") with one that is not.

          • 3 weeks ago
            Anonymous

            OK, but if you're measuring the difference between two worldlines without reference to some objective thing how can you tell which is going faster and which is going slower? I'm asking how this answers the central question, which is why the satellite's clock moves slower rather than faster.

          • 3 weeks ago
            Anonymous

            One clear way is to synchronize the clocks on Earth, send the satellite up, and then bring the satellite back to Earth and test how much time has elapsed. In spacetime this is like two worldlines that begin and end at the same point.

            This isn't so easy in practice to retrieve the satellite, but you can design the satellite to send a pulse at some predetermined proper time interval. If the satellite is staying a fixed distance from Earth there will be no Doppler effect and the rate at which you receive signals is a good indicator of the relative scaling of proper time. If the person on Earth sends signals the satellite will also receive them sped up rather than slowed down, so there is no paradox, despite the naive application of time dilation formulas.

          • 3 weeks ago
            Anonymous

            I'm not asking how the results of the experiment are obtained, I'm asking how your explanation accounts for the fact that the satellite clocks move slower, rather than moving faster. What does the use of worldlines tell us about why the satellite is moving faster, instead of the earth moving faster?

          • 3 weeks ago
            Anonymous

            In ordinary 3D space if you have two paths that begin and end at the same point the more curved one will have more path length. A "straight" path can be defined as the path of minimum length connecting two points.

            In spacetime there is similar geometry. A worldline is a path in spacetime, and its path length is the same thing as the proper time. But spacetime is not quite the same as ordinary 3D space (it has "Lorentzian signature" if you want to hear some jargon), and there is a sign flipped so that the straightest path has the most proper time rather than the least.

            Worldlines makes things clear that the proper time is something geometric that doesn't depend on frame (so there can be no paradox), and it also makes it clear that the more you move around between two fixed points the less proper time you will have

          • 3 weeks ago
            Anonymous

            So the satellite is moving faster because it has a more curved worldline, and an object has a more curved worldline if it's moving faster? That's just a tautology.

          • 3 weeks ago
            Anonymous

            I never said anything like that. You only spent 2 minutes reading my post, and I spent longer than that writing it. If you want to ask me a good question after taking the time to understand what I wrote, then I might answer again.

          • 3 weeks ago
            Anonymous

            Your explanation is gobbledyasiatic, are you ESL? What is "proper time", how can something "have proper time"? How can time belong to something? I asked a simple question and you gave me a bunch of jargon as an answer and then got frustrated that I don't immediately understand it.

          • 3 weeks ago
            Anonymous

            Proper time is a basic term in special relativity. It means the time a clock moving along a path actually measures. It is something that is obviously physical, whereas often in naive treatments of special relativity people are dealing with some unphysical coordinate time.

          • 3 weeks ago
            Anonymous

            OK, so the satellite "has more proper time", and the clock on it moves slower, because it's taking a straighter line through spacetime than earth. Why is it taking a straighter line through spacetime than earth?

          • 3 weeks ago
            Anonymous

            >OK, so the satellite "has more proper time", and the clock on it moves slower, because it's taking a straighter line through spacetime than earth
            You have the details wrong, but yes this is roughly what I am saying. (The earth is the one taking the straighter line but the clock on the satellite moves slower)

            >Why is it taking a straighter line through spacetime than earth?
            This is where you have to appeal to physics. If you can plot the paths in spacetime in any coordinate system, there is a way to calculate the length along the path (which again is equal to the time that has actually elapsed) using something called a "metric."

            This metric is the closest analogy to the universal aether you are looking for in the sense that it gives a clear answer to how much time elapses, but it is a little different since it takes the same form in boosted inertial frames.

  4. 3 weeks ago
    Anonymous

    The satellite is accelerated whereas the earth is approximately not on this scale. An accelerated worldline is curved in spacetime so this is an unambiguous concept which doesn't depend on choice of observers or frames (which is early 1900's language for spacetime coordinate systems, but for some reason the latter is never taught at the popsci level).

  5. 3 weeks ago
    Anonymous

    Time is just a illusion and doesnt exist, and relativity is not what ~~*they*~~ made you think

  6. 3 weeks ago
    Anonymous

    A clock on satellite moves at the same speed as the clock on earth

  7. 3 weeks ago
    El Arcón

    The clock moves at the same speed, but time goes slower, and that effects the clock's speed because speed is distance divided by time.

    • 3 weeks ago
      Anonymous

      Why doesn't time go slower here on earth, rather than on the satellite?

  8. 3 weeks ago
    Anonymous

    I really like this video.

    • 3 weeks ago
      Anonymous

      Yeah, watching now and it's basically the argument on the Einstein aether theory wiki page, which I agree with. I was curious what the refutation of it might be.

      Say instead that there are two spacecraft passing each other in space. Neither is accelerating and there are no gravitational fields.
      Both see the clock in the other spacecraft running slow. Because it's moving with respect to them. They don't have to agree.

      OK, that's an answer to my original question. Both objects perceive the other object as moving faster than themselves. So if you brought the two clocks to the same place, would the one from the faster spaceship (the one with engines that provided more thrust) be behind, or would they tell the same time?

      • 3 weeks ago
        Anonymous

        >So if you brought the two clocks to the same place, would the one from the faster spaceship (the one with engines that provided more thrust) be behind, or would they tell the same time?
        The one which accelerated in order to meet would be slow.

        • 3 weeks ago
          Anonymous

          Accelerated relative to what? If the two ships are judged relative to each other, and don't use a third object to triangulate, it's impossible to say which is accelerating and which is not.

          • 3 weeks ago
            Anonymous

            Acceleration is not relative. It's quite easy to measure acceleration, e.g. with an accelerometer which measures the fictitious force on some objects. You feel the acceleration when a car goes round a corner.

          • 3 weeks ago
            Anonymous

            Are you high? You don't feel acceleration in a vacuum. You feel acceleration in a car because the car is slowing down and you're still moving forward, or vice versa. If you don't physically touch anything accelerating at a different rate than you, you can't perceive whether you're accelerating, or it is. Imagine you're standing on a ball in space. Another ball in the distance gets smaller. Are you moving away from it, or is it moving away from you?

          • 3 weeks ago
            Anonymous

            You're mistaken

          • 3 weeks ago
            Anonymous

            An accelerometer measures the force applied to a separate piece within itself, then divides it by the pieces's mass. Imagine that separate piece is the passenger, and the accelerometer is the car. If the piece was tightly fixed to the accelerometer then you wouldn't measure any force. It's because it moves inside the accelerometer that you can get the force.

          • 3 weeks ago
            Anonymous

            >If the piece was tightly fixed to the accelerometer then you wouldn't measure any force. It's because it moves inside the accelerometer that you can get the force.
            You would still measure a force. If there was no force the piece would not accelerate with the rest of the device.

          • 3 weeks ago
            Anonymous

            >You feel acceleration in a car because the car is slowing down and you're still moving forward, or vice versa.
            Yes that is what a fictitious force is.
            >If you don't physically touch anything accelerating at a different rate than you, you can't perceive whether you're accelerating, or it is.
            If you don't touch it you aren't accelerating. The fact that your body will slam into the floor of the rocket is proof it is accelerating. Drop a ball, if it falls to the floor the rocket is accelerating.
            >Imagine you're standing on a ball in space. Another ball in the distance gets smaller. Are you moving away from it, or is it moving away from you?
            We're talking about measuring if you are accelerating.

          • 3 weeks ago
            Anonymous

            So how can you determine whether the ball you're standing on in my example is accelerating, or if the other ball is?

          • 3 weeks ago
            Anonymous

            Never mind, I get what you're saying

          • 3 weeks ago
            Anonymous

            >You feel acceleration in a car because the car is slowing down and you're still moving forward, or vice versa.
            Yes that is what a fictitious force is.
            >If you don't physically touch anything accelerating at a different rate than you, you can't perceive whether you're accelerating, or it is.
            If you don't touch it you aren't accelerating. The fact that your body will slam into the floor of the rocket is proof it is accelerating. Drop a ball, if it falls to the floor the rocket is accelerating.
            >Imagine you're standing on a ball in space. Another ball in the distance gets smaller. Are you moving away from it, or is it moving away from you?
            We're talking about measuring if you are accelerating.

            I mean I get how you'd be able to tell. The ball you're on would be exerting forces on you

  9. 3 weeks ago
    Anonymous

    Wait a minute, how could you tell whether the ball is accelerating into you or you or accelerating into the ball?

    • 3 weeks ago
      Anonymous

      If you're not touching anything then you shouldn't accelerate. Hence it's the ball.

  10. 3 weeks ago
    OP

    It turns out the thing I was talking about is the twin paradox and the idea that there's a absolute inertial frame of reference isn't that controversial. Some sources think it's aether but others think it's the sun total of all the other stuff in the universe. Some physicists doubt it and instead say it's "acceleration" that makes the slow-aging twin or the slow-running clock run slow, but they have to specify acceleration relative to what and that's where they run into difficulties.

    https://en.m.wikipedia.org/wiki/Twin_paradox

  11. 3 weeks ago
    Anonymous

    Maybe what you're talking about is reciprocity
    https://en.wikipedia.org/wiki/Time_dilation#Reciprocity

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