In any small region of space (technically, a "coordinate chart" in general relativity), the laws of physics themselves propagate information only at the speed of light. Meanwhile, objects passing right by you have well-defined speeds, that can easily be measured with two synchronized stopwatches held a short distance apart any process that the laws of physics propagates past you will be moving at most at the speed of light. The issue, as I understand it, is that speeds of objects far away from you (the observer) may be ambiguous or ill-defined, if space-time is doing strange things in between you and the object. General relativity tells you we are attracted to the position the Sun would have now if it wouldn't have accelerated within the last 8 minutes. The gravitational influence comes from the Sun as it was 8 minutes ago, but if you care about this then you also have to take into account the effect of its motion. Number 4 doesn't seem to follow from the first three, can someone explain why gravity can't propagate faster than the speed of light?įor the same reason as (1), the speed of light is the limit on every actual speed of propagation of anything.įor example, I've heard it said that the earth doesn't orbit the Sun's current location, it orbits where the sun was 8 minutes ago. Gravity waves are things like waves on the surface of an ocean. Gravity/gravity waves travel at the speed of light The distance between things nearby (where absolute speed values would be a more useful concept) does not. The distance between things with a large distance can increase faster than the speed of light. It doesn't make sense to call it a speed. The expansion of the universe can happen faster than the speed of light Thus it would be about eight minutes before we knew that the Sun's gravitational field has disappeared.Unlike light, gravity is not a force carried by particles traveling through space, it's caused by the distortion of spacetime itself Dr Mike Wheatland, School of Physics, University of SydneyĪ: Although gravitational waves have not yet been observed, we think that such a change in gravitation fields will travel in much the same way as light or other electromagnetic waves travel, and with the same speed. There isĬurrently a concerted effort to try to detect these waves experimentally.īasically, if the Sun were to disappear, we would only know about it eight minutes later. According to General Relativity, changes in distributions of mass produce gravity waves, which communicate the changes. Prof John Lattanzio, Director, Centre for Stellar and Planetary Astrophysics, Monash UniversityĪ: Gravitational influences also propagate at the speed of light. So if the Sun were to suddenly disappear then space-time would react to that at the speed of light and in about 8 minutes the Earth would head off in a straight line, along a tangent to its orbit at the time that the gravitational force from the Sun disappeared - ie about 8 mins after the Sun itself disappeared, and at the same time that things suddenly got very dark! Formally the effects of gravity are manifested through its effect on the shape of space-time, and this distortion moves at the speed of light. This was postulated by Einstein, and was first measured in 2003 by scientists at National Radio Astronomy Observatory in Charlottesville, Virginia. The gravitational force also travels at the speed of light. A: No, gravity does not travel faster than light.
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