How Gravity Changes Time: The Effect Known as Gravitational Time Dilation

November 16, 2015 | Joanne Kennell

Artist's concept of a probe orbiting Earth to measure the distortion of space-time
Photo credit: NASA

Gravity is not just a force.

Did you watch the movie Interstellar and come out wondering how any of it was possible?  It is mind-boggling to comprehend that one hour can pass by on one planet while seven years pass by on Earth.

The explanation comes down to what scientists call Gravitational Time Dilation.  This effect measures the amount of time that has elapsed between two events by observers at different distances from a gravitational mass.  In other words, time runs slower wherever gravity is strongest, and this is because gravity curves space-time.

Think of it this way — time follows a simple equation:

speed = distance / time

Light (in this case, speed) is always constant and travels at a speed of 180,000 miles per second.  Imagine two beams of light: one in a weak gravitational field traveling between points a and b, and the other in a strong gravitational field traveling between points c and d.


Diagram of Gravitational Time Dialation

The path between c and d is longer due to the curving of space and time so it takes longer for light to travel between the two points.  This effect has been proven by several experiments and is used to run and maintain something most of us use almost every single day: GPS.

Global Positioning System (GPS) satellites are positioned about 12,550 miles above Earth’s surface and therefore are not as close to Earth’s gravitational field.  The clocks on these satellites tick faster than the clocks on Earth’s surface so scientists have put a correction into the satellite programs to ensure that the GPS data sent back to Earth’s surface have matching times.  Without this correction, GPS satellites would not be the useful tool that we know them to be.

Are you hoping that Gravitational Time Dilation will help you live longer if you decided to travel to some distant planet with a strong gravitational field?  Even if that were possible (and it is not with our current technology), you would only be living longer relative to Earth.  Humans still only have a lifespan of 70 – 100 years.

Taking a look at our solar system and the planet with the largest gravitational mass, Jupiter, how much longer could we expect to live relative to Earth if we were able to move to there?  According to Neil deGrasse Tyson, it would only be a few minutes.

You might also like: Is Time Real?

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