# Time dilation at zero velocity (and zero gravity)

From what I've learned, the more an object travels closer and closer to the speed of light, the more time will slow down for that object.. at least from an outside perspective..

It was shown that atomic clocks run slower in high speed orbit than clocks on earth.. I assume that the rate of radioactive decay (for example) is also slowed down at high speeds (correct me at any time, please).

We are moving through space right now at 760 miles per second (0.40771% the speed of light), which I can only assume is our current "cosmic clock", which also regulates how fast radioactive decay happens on earth (if we continue with that example).

When an astronaut is traveling at high velocity, his/her velocity is being added to the overall velocity of our galaxy moving through space, right?

So my question is this:

What will happen if an object were to stay completely stationary in space-time? Far away from any galaxy.. Will time go infinitely fast for that object? Will it instantly decay?

Since space is expanding, I realize you can't really stay "stationary".. but I mean: not having velocity of moving through space.

Thanks :)

• What people don't understand about relativity is that speeds are relative. And that time dilation is for an externar observer. Ansewer you question: you don't have to go far away to see a stationary object, my chair is stationary wrt the floor. And time goes at the same rate of any object in the Univers (proper time is always the same). – jinawee Mar 23 '14 at 9:37
• Your entire question seems premised on the existence of an absolute rest frame (e.g., "not having velocity through space) but there is no absolute rest frame. Motion is relative thus we can properly speak of the relative motion of two objects but not the motion of an object so the notion of a "completely stationary" object isn't meaningful. – Alfred Centauri Mar 23 '14 at 16:04

You're messing up with simple time dilation. Time intervals are relative quantities. Two observers may not be agree with measured time intervals of an event. You see other moving observer's time dilated. Also, you see other observer's time dilated if she is deep in Gravity well than you are. Meaning, you find other observer's measured time interval more than your own measurement result of the same event. That's it.

Now, come to Radioactive decay: You measured half-life of a substance on Earth. Another observer who is independent of motion of Earth etc and far from any Gravity well (the notion of stationary is irrelevant), would find your measured half-life more than hers.

• Would she find the OP's measured half-life of a substance to be more than her's because the OP (and his substance) is experiencing more time dilation? So since time runs slower for the OP and his substance, it will take longer for the substance to expire. If the substance's life is thought of as a "timeline", does time dilation cause it to move slower through this timeline? – Inertial Ignorance Mar 4 '18 at 21:33

There is no absolute stationary object, an object may only be stationary with regard to an observer. If e.g. the relative velocity of an object is zero in our reference frame, we observe an object which is not moving with regard to our own reference frame. In this case Lorentz factor is 1, that means that there is no time dilation at all.

by definition, any object is stationary relative to itself, regardless of any other frame. from the perspective of that object, no dilation exists, and time is experienced at it's full normal rate rather than a fractional amount as relative to another objects perspective.

the rate of time doesn't increase to infinity, but rather can decrease by a fractional amount (aproaching infinity as a denominator). Dilation is not a linear scale, but a fractional one, so all observations are a fraction of the whole due to dilation, rather than increasing to infinity.

Theoretically speaking, of course, if your true linear speed with respect to the true center of the universe was zero, you would be experiencing true time. Even on Earth, who's movement is what we base our time (e.i. seconds, days, years, etc) off of, we theoretically would be experiencing time dilation based on Lorentz, assuming that at a true zero velocity is possible. However, zero velocity and zero gravity are both impossible due to the fact that no matter where you are, there is always gravity acting upon you, and because there is alway gravity, you will always have a velocity. Theoretically speaking though, zero velocity is a concept which would require an object to cancel all gravities acting upon it by having a thruster of sorts pushing it equal and opposite of all gravities, therefore having velocity via canceling all gravity. However, as interesting of an idea that is, it would be impossible to calculate every single gravity acting upon it due to the expansion of the universe never stopping and never predictable. Also, all of this may or may not be correct due to the fact that I am a highschooler without connection to any major person in the physics world, so all of this is just my own speculation and my own theory, as far as I know. Thank you.

• with respect to the true center of the universe - Not only is there no center of the universe, but there is no absolute frame of reference. I would also advise not writing answers based on speculation. – HDE 226868 Nov 7 '15 at 23:02
• My bad on the second part. However, assuming that the big bang is correct, there would have had to have been a center point in the Oth dimension because it would have no length, width, or height, then the bang would cause the universe to be created exponentially from the center point in whatever shape it expands as. Also, if it were possible to watch the universe from a third person point of view and rewind every, it would eventually reach a point which it started from. And again, my apologies because this is all speculation from a highschooler but sometimes think out of the box, Thank you – MstrKyleX Nov 8 '15 at 5:32
• I appreciate the contriteness; there's still one thing you missed: The Big Bang didn't happen at a point. – HDE 226868 Nov 8 '15 at 14:25

Lorentz factor, the speed-dependent dilation function, is $$\lim_{v \rightarrow 0} \sqrt{1-v^2/c^2} = \sqrt{1-0^2/c^2} = \sqrt{1} = 1.$$ We see a considerable time dilation at v=0.

• $1$ means no time dilation at all. – jinawee Mar 23 '14 at 9:37