# Is Time Compression possible?

## Main Question or Discussion Point

Time Compression - the opposite of Time Dilation.

Similar to Lorentz Length Expansion

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ghwellsjr
Gold Member
Time Compression - the opposite of Time Dilation.

Similar to Lorentz Length Expansion
Ignoring gravity, in an inertial reference frame, stationary clocks tick at the same rate as the coordinate clocks. Moving clocks tick slower than the coordinate clocks. The faster they move the slower they tick. So in an inertial reference frame, clocks can only experience time dilation.

This means that any inertial clock will observe all other clocks to be ticking at its same rate (if there is no relative motion between them) or ticking slower than its rate (if there is relative motion).

However, a non inertial clock can observe other clocks to be ticking faster than its rate. A simple example is a clock that is traveling in a circular path. Its time will be slowed down compared to any coordinate clock which means that it will observe those clocks to be ticking faster than it own rate.

It's only when you have two inertial clocks that they each see the other one as ticking slower than their own.

Does this make sense to you?

Simon Bridge
Homework Helper
As in the resolution to the Twin's Paradox ... it's how the travelling twin ends up younger.

pervect
Staff Emeritus
Time Compression - the opposite of Time Dilation.

Similar to Lorentz Length Expansion
Lets add one important clarification/assumption. I'll assume that you want one observer to be on the Earth, and a second observer to start and end co-located with the Earth observer, but to experience more time on their wristwatch than the earth observer experiences.

With this assumption about what you're asking, you can get an inisgnificant amounts of "time compression" by going on a rocket trip into deep space, as far away from any gravity wells as you can get. Insignificant being time compression by a factor of 1.00000001

In theory you might get larger time compression if you could find a large enough quantity of exotic matter and use it to create a sufficiently steep gravity "hill" (the opposite of a well). It's unclear if such exotic matter actually exists in the real universe, though, and especially unclear if it exists in a form usable to create time-compression.

Lets add one important clarification/assumption. I'll assume that you want one observer to be on the Earth, and a second observer to start and end co-located with the Earth observer, but to experience more time on their wristwatch than the earth observer experiences.

With this assumption about what you're asking, you can get an inisgnificant amounts of "time compression" by going on a rocket trip into deep space, as far away from any gravity wells as you can get. Insignificant being time compression by a factor of 1.00000001
Here is a version of the "travelling twin" ageing more, without using gravity. The stay at home twin remains at the rear of Rindler rocket while the travelling twin is launched towards the nose of the rocket. The travelling twin is inertial in this case (after launch) and turns around when he reaches apogee near the nose of the rocket and free falls back to the rear. Upon his return the travelling twin will have aged more than the twin that remained at the rear of the rocket.

Ignoring gravity, in an inertial reference frame, stationary clocks tick at the same rate as the coordinate clocks. Moving clocks tick slower than the coordinate clocks. The faster they move the slower they tick. So in an inertial reference frame, clocks can only experience time dilation.

This means that any inertial clock will observe all other clocks to be ticking at its same rate (if there is no relative motion between them) or ticking slower than its rate (if there is relative motion).

However, a non inertial clock can observe other clocks to be ticking faster than its rate. A simple example is a clock that is traveling in a circular path. Its time will be slowed down compared to any coordinate clock which means that it will observe those clocks to be ticking faster than it own rate.

It's only when you have two inertial clocks that they each see the other one as ticking slower than their own.

Does this make sense to you?
So...it IS POSSIBLE. Just depends on your frame of reference.

But this is weird, now we need to figure out exactly when Time Dilation or Compression would occur.

If Time Compression is possible, is Length Expansion also possible?