Time dilation in freefall?

[losfomot]

When you are in freefall or in orbit around a planet, you no longer feel gravity... you become weightless. Do you still experience time dilation at the same rate as you would if you could feel gravity.

 

For clarity....

 

John is standing on a platform on the moon. Jane is orbiting the moon at the same height as the platform that John is standing on. Does time pass at the same rate for both Jane and John?

 

Damn... I can see I'm going to get into some trouble with the fact that Jane and John are moving WRT one another... hopefully you know what it is I am asking.

[BlackHole]

I think time should pass faster for Jane.

 

The difficult question is whether the gravitational field is producing such effects independent from the machines used to observe the effect, or is the gravitational field simply altering the machines that observe a specific physical scenario and the field is not actually altering the physical scenario as predicted by a time-dilation derivation?

 

The location of gravitational time dilation effects is somewhat controversial.

[swansont]

In a GPS satellite there is a gravitational term as well as a kinetic term in the timing correction. Does that answer your question?

[losfomot]

In a GPS satellite there is a gravitational term as well as a kinetic term in the timing correction. Does that answer your question?

 

 

Not entirely, no.

 

The gravitational term in the timing correction could be because:

 

A- A GPS satellite is in freefall, and therefore does not experience time dilation (from the Earth's mass) while we on Earth's surface do... hence a timing correction.

 

Or

 

B- A GPS satellite is further away from the surface than we are, and therefore experiences less time dilation (from the Earth's mass) than we do... hence a timing correction.

[swansont]

Not entirely' date=' no.

 

The gravitational term in the timing correction could be because:

 

A- A GPS satellite is in freefall, and therefore does not experience time dilation (from the Earth's mass) while we on Earth's surface do... hence a timing correction.

 

Or

 

B- A GPS satellite is further away from the surface than we are, and therefore experiences [b']less[/b] time dilation (from the Earth's mass) than we do... hence a timing correction.

 

B

[geistkiesel]

Not entirely' date=' no.

 

The gravitational term in the timing correction could be because:

 

A- A GPS satellite is in freefall, and therefore does not experience time dilation (from the Earth's mass) while we on Earth's surface do... hence a timing correction.

 

Or

 

B- A GPS satellite is further away from the surface than we are, and therefore experiences [b']less[/b] time dilation (from the Earth's mass) than we do... hence a timing correction.

B

 

From teh question and answer here it appears that the time dilation experienced from a SDAT ior any orbiting object will approach the sutrface clock rate the farther from teh surface the clock is located.

 

Swansont picked the answer B, which is functionally unrelated to "velocity" the onetime definitive mark of SRT. If what the B answer implies is true then a clock originating on the earth surface and synchronized to an earth standard clock will experience a spell of dilation, from some unknown force, perhaps the acceleration force that produced the orbiting object in the first place; then some maximum state, or rate, is achieved, and from then on as the clock moves away from the earth surface and gravitational effects, the clock rate will approach, increase to match, the earth surface standard clock rate?

 

Weirder than weird. I would like to see some mathematical SRT structure that produces this gem of a result.

 

I don't believe it, but then belief is nothing . . .si it?

 

Geistkiesel

[geistkiesel]

When you are in freefall or in orbit around a planet' date=' you no longer feel gravity... you become weightless. Do you still experience time dilation at the same rate as you would if you [b']could[/b] feel gravity.

 

For clarity....

 

John is standing on a platform on the moon. Jane is orbiting the moon at the same height as the platform that John is standing on. Does time pass at the same rate for both Jane and John?

 

Damn... I can see I'm going to get into some trouble with the fact that Jane and John are moving WRT one another... hopefully you know what it is I am asking.

If you look closely at SRT postulates, SRT does not apply in accelerating frames. As the orbit around earth is not a straight line SRT cannot be used to analyze any orbital motion. I suppose SRT should be versatile enough to handle curved motion that cannot be measured as such; Meaning that there is no physical measurment that can detect a curve in the apparent local straight line motion.

 

But SRT will not allow this, will it?

Geistkiesel

[swansont]

If you look closely at SRT postulates' date=' SRT does not apply in accelerating frames. As the orbit around earth is not a straight line SRT cannot be used to analyze any orbital motion. I suppose SRT should be versatile enough to handle curved motion that cannot be measured as such; Meaning that there is no physical measurment that can detect a curve in the apparent local straight line motion.

 

But SRT will not allow this, will it?

Geistkiesel[/indent']

 

But GR does, and SR is a subset of GR. There is a kinetic term of v

²

/2c

²

along with the potential term GM/rc

²

[swansont]

I don't believe it

Regardless of your belief, it is true.

 

When the first satellite with a cesium clock went up, there were those that did not think the clocks had to be corrected. So they sent up the satellite with the ability to change the oscillator frequency from the ground value to the nominal orbit value.

 

They launched the satellite that was operating at the correct frequency on the ground and sure enough it ran fast when in orbit, by the amount predicted by relativity (the kinetic dilation term is smaller than the gravitational term in that orbit), to about 1%. So they switched on the frequency correction, and it was fine. (more)

[geistkiesel]

In a GPS satellite there is a gravitational term as well as a kinetic term in the timing correction. Does that answer your question?

Where in the GPS algorithims is the gravitational and kinetic term corrected re the timing circuits? Kinetic, you mean velocity, or energy, what, I am not clear on this?

 

Geistkiesel

[swansont]

Where in the GPS algorithims is the gravitational and kinetic term corrected re the timing circuits? Kinetic' date=' you mean velocity, or energy, what, I am not clear on this?

 

Geistkiesel [/indent']

 

 

Please read the information before responding. Post #8 and the link in post #9.

[geistkiesel]

In a GPS satellite there is a gravitational term as well as a kinetic term in the timing correction. Does that answer your question?

Swansont,

 

It isn't quite as simple as you may suggest.

Here is a quote.

 

"Second, the effect is also demonstrated by the reference clocks in the GPS tracking stations. The tracking stations provide the data which are used to compute the predicted GPS orbits for uploading and subsequent broadcast of the estimated GPS satellite position. It is observed that all clocks at sea level in an earth-centered non-rotating frame run at the same rate. A clock at sea level at the equator runs slower because of the earth's spin, but that same spin via centrifugal force causes the earth to assume an oblate shape so that the clock at the equator is located at a higher gravitational potential. At this higher gravitational potential, the clock runs faster per equation (3). The net result is that the velocity effect and the gravitational-potential effect exactly cancel, and the equatorial sea-level clock runs at the same rate as the polar sea-level clock."

 

Geistkiesel

[geistkiesel]

In a GPS satellite there is a gravitational term as well as a kinetic term in the timing correction. Does that answer your question?

Swansont,

These effects canel each other.

 

Geistkiesel

[geistkiesel]

But GR does, and SR is a subset of GR. There is a kinetic term of v²/2c² along with the potential term GM/rc[sup']2[/sup]

Swansont,

SR may be a subset of GR, but this does not fix the fact that SR is an inertial system. Also, it seems you missed the part where the gravitational and kinetic terms cancel out.

 

The fact that GPS uses a preferred frame doesn't bother SR people much because SR doesn't apply , say some. In any event time dilation is a relative motion effect and the fact that the GPS uses the ECEF places any dilation questions into the camp of Lorentz transformations, not SRT. This means of course that SRT depends on the relative motion of inertial fframes, which sxcludes SRT from any consideration as being applicable to GPS.

 

There us a significant difference in the two theoretical systems.

Geistkiesel

[swansont]

Swansont' date='

 

[indent']It isn't quite as simple as you may suggest. Here is a quote.

 

"Second, the effect is also demonstrated by the reference clocks in the GPS tracking stations. The tracking stations provide the data which are used to compute the predicted GPS orbits for uploading and subsequent broadcast of the estimated GPS satellite position. It is observed that all clocks at sea level in an earth-centered non-rotating frame run at the same rate. A clock at sea level at the equator runs slower because of the earth's spin, but that same spin via centrifugal force causes the earth to assume an oblate shape so that the clock at the equator is located at a higher gravitational potential. At this higher gravitational potential, the clock runs faster per equation (3). The net result is that the velocity effect and the gravitational-potential effect exactly cancel, and the equatorial sea-level clock runs at the same rate as the polar sea-level clock."

 

Geistkiesel

[/indent]

Yes, I've noted in several posts that in the ECI frame, all ideal clocks on the geoid run at the same rate. You do realize that by "at sea level" this is referring to terrestrial clocks, right?

[swansont]

Swansont' date='

These effects canel each other.

 

Geistkiesel

[/indent']

 

Not on the GPS satellites they don't. Refer to the link - the effects cancel at about 9545 km. The GPS orbit is higher, about 20,000 km.

[geistkiesel]

Not entirely' date=' no.

 

The gravitational term in the timing correction could be because:

 

A- A GPS satellite is in freefall, and therefore does not experience time dilation (from the Earth's mass) while we on Earth's surface do... hence a timing correction.

 

Or

 

B- A GPS satellite is further away from the surface than we are, and therefore experiences [b']less[/b] time dilation (from the Earth's mass) than we do... hence a timing correction.

losfomot

 

What exactly do you mean " ...hence timing correction."

 

GHeistkiesel

[swansont]

losfomot

 

What exactly do you mean " ...hence timing correction."

 

GHeistkiesel

 

 

GPS clocks' synthesizers must run at a different frequency in orbit than when they are on the ground in order to run at the same rate as the ground clocks. It's in the link I provided.

[geistkiesel]

In a GPS satellite there is a gravitational term as well as a kinetic term in the timing correction. Does that answer your question?

Swansont, There may be terms in SRT, but these effects cancel each other. I understand that there is no software correction to the kinetic and so-acalled ghravitational effects on GPS clock timig circuits.

[swansont]

[indent']Swansont, There may be terms in SRT, but these effects cancel each other. I understand that there is no software correction to the kinetic and so-acalled ghravitational effects on GPS clock timig circuits.[/indent]

 

 

No, on the GPS satellites they don't cancel. I already pointed this out in post #16.

 

The v²/2c² term does not equal the change in the GM/rc² term. This is really pretty simple algebra, and there's a graph (although it's really small for some reason) in the link I gave, that shows the overall correction as a function of orbit size.