If there's nothing in space or say free space the time would move on faster than in region with gravity because gravity bends space-time. Isaac Newton saw time as passing at the same rate for all observers. This was not quite true. Relativity says that time is the fourth dimension of spacetime. This has some profound consequences.
He also showed that mass and energy cause spacetime to curve. Gravity is the effect of this curvature. Both velocity and mass cause time to slow. An observer on a fast moving ship or in a strong gravitational field will experience time passing normally.
An external observer will see time passing more slowly on the fast moving ship or in the gravitational field. Something curious happens to time when in orbit around Earth or anything else. The orbital speed causes time to slow. The reduced gravity by being in orbit rather than on the surface causes time to speed up. These effects cancel out at an altitude of half of the radius of planet. So, astronauts in low orbit on the ISS age slightly slower than people on the Earth's surface because the velocity component of time dilation is greater than the effect of reduced gravity.
The clocks on GPS satellites in high orbit run faster than on the Earth's surface because of the reduction in gravity has a bigger effect than orbital speed. These satellites have to have their clocks slowed down to match surface time. The theory of relativity explains gravity as the effect of mass on the space time continuum. The effect of mass on space predicted that light would be bent as it entered a gravitational field.
The latest video from MinutePhysics addresses a famous conundrum known as the Twin Paradox , where both an observer on Earth and an observer on a rocket would consider time to be going more slowly, because each would believe the other person to be doing the relative movement.
In the example of a rocket flying out and returning to Earth, it's the rotation of time as the rocket turns that solves the paradox, as well as the acceleration and deceleration of the returning traveller the charts in the MinutePhysics video help explain this principle more clearly. These ideas have been backed up by some solid scientific experiments - including flying atomic clocks above Earth's surface on planes, where, sure enough, the recorded times are different to those logged on Earth.
Of course, the fact that Mark and Scott Kelly are twins is significant for reasons other than examining time dilations while out in space. General relativity theory makes various predictions about the behavior of space and time. One of these predictions, put in everyday terms, is that the stronger the gravity, the slower the pace of time. Such a statement goes very much counter to our intuitive sense of time as a flow that we all share. Time has always seemed the most democratic of concepts: all of us, regardless of wealth or status, appear to move together from the cradle to the grave in the great current of time.
But Einstein argued that it only seems this way to us because all humans so far have lived and died in the gravitational environment of Earth. We have had no chance to test the idea that the pace of time might depend on the strength of gravity, because we have not experienced radically different gravities. Moreover, the differences in the flow of time are extremely small until truly large masses are involved.
An ingenious experiment in used the most accurate atomic clock known to compare time measurements on the ground floor and the top floor of the physics building at Harvard University. For a clock, the experimenters used the frequency the number of cycles per second of gamma rays emitted by radioactive cobalt.
This is precisely what the experiments observed. Later, atomic clocks were taken up in high-flying aircraft and even on one of the Gemini space flights. In each case, the clocks farther from Earth ran a bit faster. Every smartphone or device that synchronizes with a GPS must correct for this as we will see in the next section since the clocks on satellites will run faster than clocks on Earth.
It takes longer because spacetime is curved in the vicinity of the Sun. The smaller the distance between the ray of light and the edge of the Sun at closest approach, the longer will be the delay in the arrival time. In November , when the two Viking spacecraft were operating on the surface of Mars, the planet went behind the Sun as seen from Earth Figure 1.
Scientists had preprogrammed Viking to send a radio wave toward Earth that would go extremely close to the outer regions of the Sun.
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