# Time dilation

1. Aug 2, 2009

### jreelawg

I was thinking that as far as I know, an atomic clock, and a mechanical clock, or a tuning fork clock might be affected differently by gravitation and acceleration. Is there any experimental verification of this?

I'm trying to figure out if atoms will decay faster and that is it.

Or if, your body ages faster all together, but your mind is the same age.

Or, if your mind, body and atoms all slow down together?

Are other forces affected by gravity, for example, covalent bonds? Magnetism?

Last edited: Aug 2, 2009
2. Aug 2, 2009

3. Aug 2, 2009

### jreelawg

But is there any experimental proof?

What is the connection between the rate atoms emit electrons, and the natural frequency molecules vibrate at, or how fast salt dissolves in water? Where does the conclusion come from?

4. Aug 2, 2009

### meopemuk

The universality of the gravitational time dilation can be demonstrated on the following simple example.

Take a two-level quantum system in free space. The energies are $E_i$ and $E_f$. The only time-dependent process in this case is the oscillation between the two levels with characteristic frequency $(E_i - E_f)/\hbar$.

To get the energy levels ($E_i', E_f'$) of the two-state system on the Earth surface we need to add the gravitational potential energy

$$E_i' = E_i - \frac{GME_i}{Rc^2} = E_i (1 - \frac{GM}{Rc^2})$$
$$E_f' = E_f - \frac{GME_f}{Rc^2} = E_f (1 - \frac{GM}{Rc^2})$$

where $E_i/c^2$ and $E_f/c^2$ are gravitational masses of the two states, M and R are the Earth's mass and radius.

This means that in the gravitational field the energy separation between the levels and oscillation frequency reduce by the universal factor of $1 - \frac{GM}{Rc^2}$.

For more complex systems (like dissolution of salt in water) the argument is basically the same: All energy separations decrease by the universal factor $1 - \frac{GM}{R}$, and rates of all processes (which are proportional to these energy separations) reduce by the same factor too.

5. Aug 2, 2009

### jreelawg

I am skeptical.

6. Aug 2, 2009

### jreelawg

If you multiply two thing's by the same fraction, they will decreased by the same factor. The question is why is a universal factor assumed without experimental evidence?

7. Aug 2, 2009

### jreelawg

I still assume that if I left earth in a space ship at .9C for a while, and came back, my one one thousand count would stay in sync with my earth twin buddies one one thousand, and I would come back the same biologic maturity of my twin. If you carbon dated me, I would be much older. Is there proof of any change beyond that?

8. Aug 2, 2009

### meopemuk

As I tried to explain, the universality of time dilation comes from the fact that gravitational energy depends on object's mass (or energy divided by c^2) and nothing else. The gravity force does not depend on the chemical composition or other factors. This is the subject of the well-known equivalence principle, and the validity of this principle has been checked by accurate experiments.

Moreover, there are direct experiments in which the action of gravity on two different clocks is compared. For example, people were comparing the rates of an atomic clock and a clock based on an optical cavity oscillator during long time intervals. As Earth spun and moved around the Sun, the gravitational potential in the laboratory changed; nevertheless, both clocks varied their rates in sync. This is the experimental evidence you are looking for.

Here are some references:

S. Bize et al, "Cold atom clocks, precision oscillators and fundamental tests", http://www.arxiv.org/abs/astro-ph/0310112

C. Braxmaier, H. Muller, O. Pradl, J. Mlynek, A. Peters, S. Schiller, "Tests of relativity using a cryogenic optical resonator", Phys. Rev. Lett. 88 (2002), 010401.

9. Aug 2, 2009

### yogi

You can think of it this way - a clock sitting on the surface of the earth is accelerating -The absolute equivalence of gravity and acceleration is the cornerstone of General Relativity - born out by many experiments

10. Aug 3, 2009

### seasnake

Components under gravital pressure are going to run slower than those not under such pressure, regardless of time dilation. I can easily display this by placing my hand on top of the hands of a clock while not doing so on an identical clock. The clock whose hands are being pressurized will run slower than the non-hampered clock. Whether its an atomic clock makes no matter, as gravity pulls on all compents that have mass whether its on the inside or out.

Run this experiment, have a long rod, place a watch on both ends of the rod. Place one end of the rod under extreme pressure, but not the other. See if the increased pressure causes the clocks to run at different rates. If time dilation occurs, when you move the rod after the clock's times run apart from each other, you should notice that the pressurized end stays at its old location longer than the part of the rod that wasn't pressurized (you should see that the pressurized side kind of blurrs when it moves, while the non-pressurized size doesn't as its in a quicker time area). In fact, if time dilation occurs, it may well be hard to move the rod at all until both ends of the rods catch up to each other in time.

At this time, regardless of experimental observations, I don't think anyone has equations that don't involve flaws within in that can prove anything in terms of time dilations. If the formulas aren't concrete, then neither can be the assumptions.

Last edited: Aug 3, 2009