When you travel away from the clock at the speed of light, the clock that is not moving, looks to be running really fast, but your clock seems to be running at normal speed.

When you turn around and fly back to the clock, it still seems to be running really fast.

The clock watching your clock will think that your clock is not running in either case.

It's always interesting to see hypothetical problems presented to explain relativity using incorrect classical physics concepts. You must first define parameters based on special relativity concepts. In your example, you have three inertial frames of reference. (An inertial frame of reference moves at a constant speed without acceleration or rotation.) We'll put your so-called clock-at-rest in inertial frame of reference 1 (IFR1). (Actually, there is no preferred frame of reference in relativity.) The second inertial frame of reference (IFR2) is traveling close to the speed of light away from IFR1. (It’s impossible for an object with mass to travel at the speed of light, because it would take an infinite amount of energy.) A third inertial frame of reference (IFR3) is traveling close to the speed of light towards IFR1.

For grins, let's make IFR2 and IFR3 travel at 0.9C (90% of the speed of light). At 0.9C, relativistic parameters change by a factor of two: mass doubles, length halves, and time slows by one-half. (Actually it's closer to 0.86603C, or one-half the square root of 3 to be exact; but usually everyone just rounds up to 0.9C.)

So what do we see from IRF1? IFR1’s clock is working normally. However, IFR2’s clock and IFR3’s clock have slowed to one-half. Any radiation from IFR2 is red shifted, and any radiation from IFR3 is blue shifted.

What do we see from IFR2? IFR2’s clock is working normally. IFR1’s clock has slowed by one-half, and any radiation from IFR1 is red shifted.

What do we see from IFR3? IFR3’s clock is working normally. IFR1’s clock has slowed by one-half, and any radiation from IFR1 is blue shifted.

The relationship between IFR2 and IFR3 is more complex. It depends on how they are moving with respect to each other. If they are moving exactly away from each other at 0.9C each WRT IFR1, then you must use Einstein’s addition formula for relativistic velocities: w = (u + v)/(1 + u*v/c^2).

To answer your original question, no--the clock in the other reference frame, if it is traveling very fast WRT to your reference frame, will always slow down. Direction doesn't matter.

To answer your original question, no--the clock in the other reference frame, if it is traveling very fast WRT to your reference frame, will always slow down. Direction doesn't matter.

Jim
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Body functions(heart rate,cellular aging, or brain functions),also?

The proof of this is apparently in Particle accelerators. The half-life of a proton at "rest" is some very small part of a second. When it is accelerated up to some significant fraction of the speed of light, it sticks around for much longer.

I think you might mean neutron. (But they have half-lives around 12 minutes. They are also tough to accelerate without a charge.) Protons appear to be quite stable. There are some theories that predict an unstable proton, but so far I know of no experiment that has demonstrated such an effect. If the proton is unstable, it must have a very, very long half-life.

Another test is the muon--a more massive, unstable cousin of the electron. Muons have a half-life so short, that from where they are created in the upper atmosphere most would decay (even if they traveled at the speed-of-light) before reaching the surface of the Earth. The fact that many are found at the Earth's surface demonstrates the clock slowing effect of relativity.

Mmm. The unspoken assumption behind this is that there is an objective reality, "time". I seriously wonder if space and time "really" exist at all, or are just our way of dealing with the world. Things do get very weird at the extremes, don't they?

And reference frames are relevant even and non-relevant speeds.

You just get to use newtonian mechanics to solve your equations.

In engineering school, my dynamics prof solved everything this way. The book taught dynamics using Cartesian coordinates. He just created whatever reference frame suited the question.

It didn't occur to me until now that it might have something to do with reference frames.