How does a body "know" how to move??!!

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Not wrong if length dilation does not require time to observe... ("practical" time doesn't count does it? Or if it does then you should say that it is the practicality of measuring length dilation that requires time to perform, rather than a theoretical necessity...which is an interesting discussion in itself ..)

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Not wrong if length dilation does not require time to observe... ("practical" time doesn't count does it? Or if it does then you should say that it is the practicality of measuring length dilation that requires time to perform, rather than a theoretical necessity...which is an interesting discussion in itself ..)

Curiously enough, length has no meaning without time, on account of simultaneity

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I am prepared to believe it, if it is explained....

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rasher null

I am prepared to believe it, if it is explained....

To measure or specify a length you have to know where the other end (in relation to the first) is at the same time.

In other words the above sentence must have meaning.

So you cannot do this without time.

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mmmm .... this is the weak form of time involvment in measuring .. a practical consideration tather than a theoretical one.

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mmmm .... this is the weak form of time involvment in measuring .. a practical consideration tather than a theoretical one.

Not really its fundamental in relativity. You must have a standard ruler (ct)(with t being proper time, not coordinate time) which equates your length. As c is invariant and t being time measured on the same frame of teference (at rest) is the only ruler all observers can agree on.

Now I want you to think about the units of velocity.... Does those units suggest you don't need time or does those units indicate time is involved... Then think about different observers measuring the velocity of some massive object.

1) Do all observers agree on the velocity measurement?

2) If not why?

3) What was it about time that caused different observers to measure different velocities?

Edited by Mordred
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I am not saying all observers agree on velocity - only that RELATIVE VELOCITY can be measured without time.

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How? You need to determine the amount of time dilation to determine the relative portion.

Even without relativity the units metres/second indicate velocity requires time by the very definition of velocity.

Velocity=the rate at which an object changes its position. Rate itself is time.

Edited by Mordred
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If I can instantaneously snap an object (from severl vantage points and collate the images) and observe length dilation in 3D then I have a vector ... call it "relative velocity"

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Your still involving time in merely taking snapshots. Regardless all that means is your measuring the same object at different measurement times nothing profound about that. Its done all the time in Astronomy.

Even more important, the velocity value must be in units of metres/sec or equivalent to. Its inherent in the definition.

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WIth the doppler effect, say, you are measuring the effect of speed in an obvious way. One knows how speed (velocity) is causing the measurement by following the wave in time. The measurement is a known consequence of motion through space and time.

With length dilation, this is not so (I think...). One could therefore argue that there is a property of the object , measured by dilation, that CAUSES velocity, and is not merely an effect of it. Perhaps...

Edited by Rasher Null
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"Time is not needed to measure velocity".

Profound? Promising? Provocative? Probably neither?

The passage of time is, of course, necessary - but I could measure the velocity of a test object passing a point without any measurement of time.

I would have to stop the object to do it - but if I were allowed to fire small objects at it in the opposite direction to travel I could measure the force used over a certain distance to accelerate these objects , I would already know their mass, and thus their velocity when I launch them. I would then use how many of my fired objects were required to stop the test object.

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mmm but you are using the properties of motion to measure velocity, just like for the Doppler effect, as I mentioned in my previous post.

To clarify, I am proposing that dilation causes an object to move through space, and not vice versa.

Edited by Rasher Null
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nope doesn't work that way as there are examples of motion without any dilation

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mmm but you are using the properties of motion to measure velocity, just like for the Doppler effect, as I mentioned in my previous post.

To clarify, I am proposing that dilation causes an object to move through space, and not vice versa.

We seem to have moved on to relativistic motion from the original specification of newtonian physics.

OK

But the above proposal should be in speculations since it runs contrary to current knowledge.

It is the whole of space in a particular direction along with everything in it, that is viewed as undergoing a particular contraction (why say dilation? that is confusing).

when measured in any particular frame.

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nope doesn't work that way as there are examples of motion without any dilation

Relativity rules without exception surely?

It is the whole of space in a particular direction along with everything in it, that is viewed as undergoing a particular contraction (why say dilation? that is confusing).

when measured in any particular frame.

Given that different objects within view will be moving in different ways that seems a wrong headed way of ermmm - "viewing" things. Does anything change by abandoning that conception?

Fair point re terminology - was getting influenced by "time dilation" I guess...

Edited by Rasher Null
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Relativity rules without exception surely?

Given that different objects within view will be moving in different ways that seems a wrong headed way of ermmm - "viewing" things. Does anything change by abandoning that conception?

Fair point re terminology - was getting influenced by "time dilation" I guess...

Then perhaps you should study it more closely.

Look at the exchange between myself and Strange in this thread which already covers this exact point.

Posts 80, 82,86,87,88

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Which exact point?

Are you saying that observing length contraction can establish a line of movement, but not which of the two directions of the line the object is moving in?

Edited by Rasher Null
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Curiously enough, length has no meaning without time, on account of simultaneity

That's the reason why I have been arguing that length doesn't commute in spacetime.

To measure or specify a length you have to know where the other end (in relation to the first) is at the same time.

In other words the above sentence must have meaning.

So you cannot do this without time.

There will be only one case (condition) where the length from the first end to the other is the same as the length from the other end to the first. This would be analogous to the hairy ball thing.

If spacetime is isotropic then there cannot be multiple instances of a null field (in any particular reference frame), i.e. where a length measures the same in both directions, or where it commutes.

Which exact point?

Are you saying that observing length contraction can establish a line of movement, but not which of the two directions of the line the object is moving in?

This sounds like an argument that direction does commute in spacetime, which sounds correct to me. Distance appears to be the property that is affected by time, not direction.

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That's the reason why I have been arguing that length doesn't commute in spacetime.

There will be only one case (condition) where the length from the first end to the other is the same as the length from the other end to the first. This would be analogous to the hairy ball thing.

If spacetime is isotropic then there cannot be multiple instances of a null field (in any particular reference frame), i.e. where a length measures the same in both directions, or where it commutes.

This sounds like an argument that direction does commute in spacetime, which sounds correct to me. Distance appears to be the property that is affected by time, not direction.

Can you provide some simple example calculations to show what you mean?

Edited by studiot
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Can you provide some simple example calculations to show what you mean?

Unfortunately I can't do that without a lot more help. The best that I can offer without having some help with the algebra is a few more thought experiments and a few more analogies and abstractions.

Using the standard abstraction of an elastic surface stretched over the opening of a cylinder with a weight placed on it, we can construct a set of surface normals that include every point on the surface. We make each surface normal a vector having a magnitude equal to the gravity at that point.

Mathematically, we can define the separation between two points (in this model of spacetime) by utilizing the new 3D identity which expresses a cone as a two dimensional graph. It goes something like this:

At one of the two points we construct a cone having its axis normal to the elastic surface. The surface of this cone will bend back toward the elastic surface at a rate that is determined by the magnitude of gravity between the surface of the cone and the surface of the elastic sheet. This would be like a water fountain that sprays at a particular angle in a conical pattern in your front yard. The water will land in the yard in a ring pattern. If we construct a similar cone at the second point then it will also create a similar ring pattern in the yard.

If we can adjust the aperture of the two cones in such a manner that they both share the same angle and where they also both have a ring that lands on the other point then we have created a condition where the two points are separated by a common direction, synchronously, or absent the distortion due to time. This would be the equivalent of the geodesic of direction as opposed to the geodesic of length. Note that if your yard is not perfectly flat that this ring made by the fountain will not be a circle. This is where the idea of length falls apart with regard to time (I know... maybe it takes a leap of faith to see it, but once you see it you somehow know that it's correct.)

My experience has been that the algebra is a lot more complicated to derive than coming up with the basic theory. I don’t really have the necessary skills required to write the algebra myself, but I think that I can help with it if anyone who does possess the skills finds this to be an interesting area of inquiry.

These abstractions are merely that, abstractions, and they don’t really reflect the way that 3D space is structured in its entirety. There’s a lot more to it than this. A whole lot more. This is especially true when we get into some of the lesser understood areas of relativistic spacetime such as the question of how to go about modeling the transverse Doppler effect. I’m pretty confident that when this effect is modeled correctly that it will explain the 2$\pi$ relationship regarding dark matter.

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• 4 months later...

I don't understand why you think there is any information, code or knowledge needed for motion to occur. The information only exists in our minds when we make some observation about it. It is not inherent, or required, for motion to happen.

boy am I surprised, I found a statement from strange I agree with.

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• 4 weeks later...

Glad to see this topic is getting a bit of traction still

I felt some progress was made in satisfying my personal puzzlement over the "nature" of motion when reminded of the existence of length contraction. By observing the length contraction of an object one can, in principle at least, calculate the relative velocity of the object. although the direction will be ambiguous by 180 degrees, it seems. ??

Edited by Rasher Null
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Glad to see this topic is getting a bit of traction still

I felt some progress was made in satisfying my personal puzzlement over the "nature" of motion when reminded of the existence of length contraction. By observing the length contraction of an object one can, in principle at least, calculate the relative velocity of the object. although the direction will be ambiguous by 180 degrees, it seems. ??

I don't think observing length connection (which is not easy) would tell you anything about direction. Doppler shift could, though.

Or just measuring the velocity...

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Surely a metre cube ,say, would yield an image with different edges contracted by different amounts, for some arbitrary motion of the cube?

Edited by Rasher Null

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