Time Dilation & Frame of Reference: Who's Time Slows Down?

[ostren]

You got me with that riddle! My answer would have to be an emphatic NO -- it doesn't accelerate, as gauged in the frame of onboard occupants and instruments. It sits motionless in space and the Earth accelerates up to meet it... and no meticulous study of the behavior of light would reveal differently.

 

[juju]

Hi DocAL,

I think I have found a way to reconcile our two points of view on the basic twin paradox as given without invoking any other similar experiment.

The fact that the distance to be traveled is defined on the rest frame of the earth, points unequivocably to the fact that it is the spaceship that has been accelerated.

However, it is also this fact of the distance being in a specific rest frame that allows one to determine which clock is actually running slower. (who counts less ticks in his own reference frame with his own counter.)

juju

 

[geometer]

Geometer's assertion in his post #66 is laughable, especially since kawikdx225 just raised the very same objection in post #61 and I refuted him handily in my post #64. Please to open eyes.

You didn't refute anything, handily or otherwise. You made some kind of comment that accelerometers measure g forces? Well, that's true, but it's also trivial. Any acceleration can be expressed as some multiple of Earth's gravitational acceleration, i.e. so many gs'. They're all accelerations.

kawikdx's response was right on. Assuming that by hovering, you mean the e rocket is stationary with respect to the suface of the Earth at some point above the surface of the earth, and the only forces acting are the rockets and the Earth's gravity, the rockets produce an acceleration exactly equal to but opposite in direction to the acceleration generated by Earth's gravity. These two accelerations add to 0 then and the hovering rocket is NOT accelerating.

 

[ostren]

...accelerometers measure g forces?

.. I think you are confused about how an accelerometer works.

Well I found the definition of the device at http://www.britannica.com/eb/article?tocId=9003472&query=accelerometer&ct= and you saw the relevant passage from it I quoted. Accelerometer is a device to measure G-forces, like those felt by an occupant of a lurching car, or like those felt by astronauts during lift-off. Read it again for the first time, that definition.

It's the same principle as a bathroom scale; how much you weigh on it is an indirect measure of how many G's of downward pseudo-force you're experiencing, gravity or acceleration.. they're equivalent. If you were in freefall, ie. my clock A, the bathroom scale would indicate zero. If you were hovering, ie. my clock B, or just standing on Earth, the scale would read your usual weight, indicating that you are experiencing ONE GEE of pseudo-force.

 

[kawikdx225]

You got me with that riddle! My answer would have to be an emphatic NO -- it doesn't accelerate, as gauged in the frame of onboard occupants and instruments. It sits motionless in space and the Earth accelerates up to meet it... and no meticulous study of the behavior of light would reveal differently.

lol
An accelerometer on the falling clock will measure 9.8m/s² while an accelerometer on the street below will measure 0m/s² therefore you can conclude it was the clock that accelerated. In theory the Earth and clock both accelerate toward each other but the mass of the Earth is so big that it's acceleration is way too small to be measured.

Anyway, we seem to be at a standstill so I will disappear for a while unless a third or fourth party joins in with their opinion.

HEY MENTOR'S, can someone clear this up please!

 

[ostren]

lol
An accelerometer on the falling clock will measure 9.8m/s² while an accelerometer on the street below will measure 0m/s²

No, just the reverse is true.

 

[kawikdx225]

OK, I'm back already.

It's the same principle as a bathroom scale; how much you weigh on it is an indirect measure of how many G's of downward pseudo-force you're experiencing, gravity or acceleration.. they're equivalent.

Here is the definition of acceleration:
Acceleration is a vector quantity which is defined as "the rate at which an object changes its velocity." An object is accelerating if it is changing its velocity.

When I stand on my bathroom scale my velocity doesn't change.

If you were in freefall, ie. my clock A, the bathroom scale would indicate zero. If you were hovering, ie. my clock B, or just standing on Earth, the scale would read your usual weight, indicating that you are experiencing ONE GEE of pseudo-force.

I agree that you are experiencing one g of pseudo-force when standing on Earth but since your velocity isn't changing then you are not accelerating.

 

[chroot]

There are a number of problems with this thread.

The most significant problem is ostren's tirade that "All physical motion, bar none, is relative, with zero favoritism attached."

This is quite simply not true in relativity theory. It's a strawman. This misconception is actually one of the most common I've seen -- people seem to think that everything is relative in relativity. That's just silly, of course. There are many invariants in relativity -- quantities which appear the same for all observers.

Acceleration is not relative.

Second, I firmly suggest that you not use the Encyclopedia Brittanica as a scientific reference. It is not rigorous. You would do better to actually learn relativity from a reputable, properly rigorous book before attempting to preach to others about it.

osten, if you wish to continue posting this sort of uneducated tripe, you will need to post it to a different website.

- Warren