Does gravity actually affect time or just the mechanisms that we use to measure it?

Question

I read somewhere about an experiment where a deep shaft was excavated and a caesium clock was placed at the bottom, with an identical one at sea level. The two clocks were calibrated to the same time at the start of the experiment, and the one at the bottom of the shaft was subsequently discovered to be running at a different rate to the one at sea level (sorry if I have got this wrong - it's been a while since I read this..). Is this a case of gravity actually affecting time itself, or merely the effect of gravity on the caesium atoms used in the clock - analagous to the timekeeping of a mechanical clock being affected by its proximity to a magnetic field. Sorry if this is a stuipid question!

Answer 1

Stronger gravity can cause time dilation, in the same way that near-light-speed travel does.

http://www.iep.utm.edu/ancillaries/time-sup.htm#H15

Answer 2

I wish I could be as sure as Ryan about what gravity is. He seems to be about the only one of all the papers and texts I've read on the subject.

For one, it's not clear that warped space causes the effect we call gravity or gravity causes the warped space. The trampoline anaology is a good example of this.

When putting a bowling ball of mass m on a trampoline, the membrane warps (sags) toward the position of the ball. That represents the warp of space in a gravity field. But wait, was it the mass or the weight of the ball that caused that membrane to warp?

If the warp is caused by the mass, then the sag in the membrane will cause a marble to roll toward the ball like something was pulling it without any further energy gradient. That is, the bend in the trampoline should be enough to get the marble to roll into the bowling ball.

But that clearly is not the case is it? There has to be an energy gradient when the marble rolls toward a lower energy level. This follows because it takes a net force to get things moving and a net force exists only when there is an difference in energy due to some force field...like gravity. Ah ha, gravity has to preexist before the membrane can warp and pull the marble toward the ball. It's the weight of the bowling ball, not its mass that warps the trampoline and causes the marble to move.

Yours was not a stupid question. It is, however, a chicken or egg question...which came first, gravity that causes the warp or the warp that causes the gravity effect? I tend to believe gravity came first and that force warps space. I tend to believe there is as yet undiscovered messenger quanta that have the extraordinary property to reach out from one mass to pull another mass toward it.

There is a similar kind of thing in electro-magnetic forces. Electrons in motion create magnetic lines of flux...a magnetic field. Like magnetic forces come from electrons in motion, I can see gravitational forces coming from the yet unfound gravity particles, which, by the way, are predicted by string/M theory.

But time dialation is caused by extreme gravitational pull, whatever the source. So the higher the gravity pull, the slower time seems to click off as seen by an outside observer...someone outside that extreme gravity pull. Which place has the higher gravity pull is unclear. Gravity force, according to Newton, varies inversely as the square of the distance between two mass (e.g., the clock and the Earth's center).

So by this, one would expect the gravity pull in the hole to be greater than on the surface because the clock is closer to the Earth's center of mass. But as we drill closer, the amount of mass above the clock increases and would offset the pull from the middle of the Earth. And this is not considered by Newton's equation. But one thing is certain, in the center of the Earth, all the mass and its gravity pull would be outward, not inward/downward.

In any case, the two clocks would likely experience two different levels of gravitational pull. So their rates of time passage would differ if only by a very little bit.

This was really a very good question.

Answer 3

Okay, the changes in time are only relative to something else. So for example, if you're orbiting earth very fast, the time taken will only be less relative to someone who is on earth. The affect is caused by the fact that the speed of light is constant relative to the observer. This means that an event can seemingly happen at two different times for two different individuals- therefore time is relative. Your theory about sick people has many problems: getting them to the planet, how they would survive the intense gravity etc. Even from a hypothetical perspective it seems unlikely to have a significant difference- even the largest differences in gravitational strengths of planets will cause time dilation of a few seconds or so. As for time travel, you cannot travel backwards in time using current physics. To travel back in time, you would need to travel faster then the speed of light relative to someone else, which is impossible as it would require more then an infinite amount of energy (another side effect of light speed being constant). However, as you have realised, you CAN end up further back/forward in time relative to someone else, but you cannot travel back in time relative to your own time frame. I hope that all makes sense, it's not a simple subject to explain.

Answer 4

In order to answer your question a person needs to know why a field of gravity forms. First of all, Stephen Hawking in "A Brief History of Time," page 92, paragraph 3, states; "Like light, gravitational waves carry energy away from the objects that emit them." So, a field of gravity is a particular form of energy. This form of energy is described in the physics trilogy, which is: E = mc2, m = E/c2, and c2 = E/m. The last is that of a field of gravity or that of a field of time. It is an energy/mass relationship.

The form of energy spoken of in the equation is that of the heat energy contained within a mass. The greater the heat energy, the greater the field of gravity. Were a mass the size of our planet to have no heat energy within it, then it would have no field of gravity about it. Were the heat energy to increase, the force would increase.

Our sun expends 665 lbs/sec in order to keep the planets in place about it, and our planet expends 0.00444 kg/sec in order to keep us in place about it. There is an experiment that was performed a few weeks ago that proves a field of gravity is able to be formed and collapsed. It is found at http://youtube.com and the name of the experiment is "successful gravity experiment". It had to be posted in segments because of time restrictions, so it needs to be put back together.

Our universe is composed of physical time. It is for this reason that all events move from that of the present into that of the past at the same rate of speed. Notice in the first two parts of the physics trilogy that the "c^2" factor is the basis of each. So, the force of gravity being that of time itself (acceleration) it cannot change. What does change is the frequency of the mass exposed to greater increase of this force.

Answer 5

Dr. Spock superbly answered a very similar question yesterday; link below.

Of course, you are not asking about the effects of gravity on granddad's gravity pendulum clock; but that would be a much greater effect, having nothing to do with relativity. The speed of a gravity pendulum is directly proportional to the strength of gravity.

The relativistic time dilation affects time, itself, as we define time. Of course, we could define time in other ways, but its hard to think of a timelike parameter that would not be affected by gravity.

Answer 6

Not a stupid question at all, this is a very complex, if not somewhat theoretical field of research. But qravity does affect time itself. According to the general theory of relativity, gravity warps the space around us, and since time and space are both part of the 4-dimensional space that we live in, gravity also warps time. Hope this wasn't too confusing.

Answer 7

Gravity isn't a force, gravity is caused by the curvature of space in the presence of a large mass, like a planet the more the mass more the curve and more the gravity (picture a bowling ball on a trampoline), and since (X, Y, Z) are the visible dimensions of space and the fourth dimension is time, (X, Y, Z, Time) ... when this frabric is warped time is effected aswell.

Answer 8

Is it the difference in gravity? or the relative velocities due to the rotation and orbit of the earth that effects clocks? The one with the greater radius travelling at a greater velocity, thus as in relativity theory (my tiny grasp), the time dilation due to different relative velocities.

Answer 9

I don't think so, time is only a measurement, a measurement of the earth to go around the sun, then split into 12 (months), then in two weeks, then days, then hours.

time doesn't accually mean anything, it's just a way of measureing. therefore a clock closer to the earhs core would move at the same speed anywhere because it's still one hour.

Answer 10

It does !