# Time Dilation: Gravity's Effect on Time

• penguinraider
In summary, the conversation discusses the effect of gravity on time and the concept of time dilation. It is suggested to ask the question in a different section and a simple explanation is given for how gravity can slow down time. The concept is further explained using the example of two observers and the expression for time dilation in a gravity field is provided.
penguinraider
I'd be very happy if you'd answer this, and I'm looking more for the effect of gravity on time, rather than speed.

penguinraider said:
I'd be very happy if you'd answer this, and I'm looking more for the effect of gravity on time, rather than speed.

I suggest you ask this in the Special Relativity/General Relativity section, since this has nothing to do with QM.

Zz.

ye, this thread should really get moved to SR/GR. But this is how gravity effects time (in simple terms).

when you are in the presence of a gravitational felid, time will slow down. If you which to calculate it, you can use the Lorenz Transformation and replace "v" with the "escape velocity" of the earth. For instance...

The escape velocity of the Earth is 11265.4 meters per second. This means that you will have to travel 11265.408 to escape the gravity of the earth. But this number does not take into consideration air friction and resistance.

So if I am on eath for 1 day, it only took me 0.999999999. You can see that there is not much of an effect on time in even what seems to be a large gravitational field such as that on earth.

Perhaps somebody can explaine in further than what I did.

time dilation is the slowing of time. Ofcourse as seen by someone else, you can never notice that ur time is running slow !? however you can compare its pace with other observers by monitoring something that should run at the same pace. You can quite easily understand why gravity must slow time by considering two oberservers Alice and Bob. If Alice sits at the bottom of the eifeltower and she send photons/light at a certain frequency f straight up to Bob whos sitting at the top of the eifeltower. Since Bob has higher potential energy then Alice the light must "climb" up to Bob and thus looses some energy to the potential, now from QM we have that the energy of a photon is E=hf, where f is the number of oscillications per second. Since energy is conserved Bob will receive a photon with approx. energy E=hf-mgh=hf´ now f´ must be a smaller number then f if Bob is to be above Alice and thus Bob is experiencing "less" gravity then Alice. If Alice claims she sends light with frequency 1, that is one oscillation per second then Bob will receive less then one oscillation per second. Thus Bob will have to conclude that either Alice is lying or her time is running slower then his. Ofcourse he can make other conclusions, such as Alice watch is crazy etc.

If Alice claims she sends light with frequency 1, that is one oscillation per second then Bob will receive less then one oscillation per second.
Wouldn't Bob still receive the light at one oscillation per second?

Expression for time dilation in a gravity field:

$$\frac{\Delta t_r}{\Delta t_{\infty}}=\sqrt{1-\frac{2GM}{rc^2}$$

The equation calculates the ratio between a time interval at radius r and a time interval at infinity. G is the gravity constant, M the mass.
The Schwarzschild radius is at $$r=2GM/c^2$$

## 1. How does gravity affect time?

Gravity affects time by causing a phenomenon known as time dilation, which is the slowing down of time in the presence of a strong gravitational field. This means that time will appear to pass slower in a stronger gravitational field compared to a weaker one.

## 2. What causes time dilation?

Time dilation is caused by the warping of space-time by massive objects like planets, stars, and black holes. This warping of space-time is a result of the strong gravitational force exerted by these objects.

## 3. How is time dilation measured?

Time dilation can be measured using atomic clocks, which are very precise timekeeping devices. By comparing the time on a clock placed in a strong gravitational field with the time on a clock placed in a weak gravitational field, scientists can measure the difference in time and determine the amount of time dilation.

## 4. Is time dilation noticeable on Earth?

Yes, time dilation is noticeable on Earth, but the effect is very small due to the relatively weak gravitational field of our planet. However, it has been observed and measured using highly precise atomic clocks on airplanes and satellites.

## 5. Does time dilation have any practical applications?

Yes, time dilation has practical applications in fields such as GPS navigation and space travel. GPS satellites, which are in orbit around the Earth, experience time dilation due to their high speed and distance from Earth's surface. This must be taken into account when calculating accurate GPS coordinates. Time dilation also plays a crucial role in the accuracy of space travel and communication between spacecrafts.

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