How Fast Is Gravity?
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How long would it take for the gravitational well created by the Sun to disappear, and the Earth and the rest of the planets fly off into space? Support us at: http://www.patreon.com/universetoday More stories at: http://www.universetoday.com/ Follow us on Twitter: @universetoday Follow us on Tumblr: http://universetoday.tumblr.com/ Like us on Facebook: https://www.facebook.com/universetoday Google+ - https://plus.google.com/+universetoday/ Instagram - http://instagram.com/universetoday Team: Fraser Cain - @fcain Jason Harmer - @jasoncharmer Susie Murph - @susiemmurph Brian Koberlein - @briankoberlein Chad Weber - weber.chad@gmail.com Kevin Gill - @kevinmgill Created by: Fraser Cain and Jason Harmer Edited by: Chad Weber Music: Left Spine Down - “X-Ray” https://www.youtube.com/watch?v=4tcoZNrSveE&feature=youtu.be In the very first episode of the Guide to Space, a clean shaven version of me, hunched over in my basement explained how long it takes for light to get from the Sun to the Earth. To answer that question, it takes light about 8 minutes and 20 seconds to make the trip. In other words, if the Sun suddenly disappeared from space itself, we’d still see it shining in the sky for over 8 minutes before the everything went dark. Martians would take about 12 minutes to notice the Sun was gone, and New Horizons which is nearly at Pluto wouldn’t see a change for over 4 hours. Although this idea is a little mind-bending, I’m sure you’ve got your head wrapped around it. We’ve sure gone on about it here on this show. The further you look into space, the further you’re looking back in time because of the speed of light, but have you ever considered the speed of gravity? Let’s go back to that original example and remove the Sun again. How long would it take for the gravitational well created by the Sun to disappear. When would the Earth and the rest of the planets fly off into space without the Sun holding the whole Solar System together with its gravity? Would it happen instantly, or would it take time for the information to reach Earth? It sounds like a simple question, but it’s actually really tough to tell. The force of gravity, compared to other forces in the Universe, is actually pretty weak. It’s practically impossible to test in the laboratory. According to Einstein’s Theory of Relativity, distortions in spacetime caused by mass - also known as gravity - will propagate out at the speed of light. In other words, the light from the Sun and the gravity of the Sun should disappear at exactly the same time from the Earth’s perspective. But that’s just a theory and a bunch of fancy math. Is there any way to test this out in reality? Astronomers have figured a way to deduce this indirectly by watching the interactions with massive objects in space. In the binary system PSR 1913+16, there’s a pair of pulsars orbiting each other within just a few times bigger than the width of the Sun. As they spin around each other, the pulsars warp the spacetime themselves by releasing gravitational waves. And this release of gravitational waves causes the pulsars to slow down. It’s amazing that astronomers can even measure this orbital decay, but the even more amazing part is that they use this process to measure the speed of gravity. When they did the calculations, astronomers determined the speed of gravity to be within 1% of the speed of light - that’s close enough. Scientists have also used careful observations of Jupiter to get at this number. By watching how Jupiter’s gravity warps the light from a background quasar as it passes in front, they were able to determine that the speed of gravity is between 80% and 120% of the speed of light. Again, that’s close enough. So there you go. The speed of gravity equals the speed of light. And should the Sun suddenly disappear, we’ll be glad to get all the bad news at the same time. Gravity is a harsh mistress. Tell us a story about a time gravity was too fast for you. Put it in the comments below. Thanks for watching! Never miss an episode by clicking subscribe. Our Patreon community is the reason these shows happen. We’d like to thank Danny Yarborough, Terrence Branscombe and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenangians with Jay, myself and the rest of the team. Want to get in on the action? Click here.
Comments
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So if I am standing on the earth with the sun right above my head, I will first be attracted by the part of the earth close to me, a little bit later by the part of the earth roughly at a distance of the radius, and a little bit later by the part of the earth which was most far away from me, the other side of the earth.
In the meantime the earth has traveled some distance in its orbit around the sun, so if I would measure where the gravity would want me to go to, this would not be exactly to the center of the earth, but, if earth is traveling to the left for me, a little bit right of it. Is this correct? -
If the speed of gravity was instantaneous, surely it would be near impossible to construct an experiment to determine this?
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Gravity isn't a force, it's a state.
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Another problem with the idea that gravity travels at light speed would be that the nature of gravity and the nature of light are the same. However there is no indication anywhere that gravity is any sort of electromagnetic radiation. So why should two very different processes travel at he same speed? Something very fishy there!
NickS -
I understand that the effect (communication) of gravity between two bodies is instantaneous. If this is true, and if the two bodies are greater than a light year apart, doesn't that gravity effect (again communication) have to be faster than the speed of light?
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Doesn't mass fall faster than light across the event horizon of a black hole? Or do we not know?
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The problema still continues: why the speed of gravity and the speed of light are the same ???
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I believe the speed of light is exceeded when the attraction of the mass becomes extreme enough to prevent light itself from escaping, The Inside of Black Hole because the speed of light is limited but do we know the limits of the gravitational pull from inside of the black hole? There can be theories by putting a limit on known laws outside of it. But do we truly know what really makes a black hole work as it does? I think black holes break the limits and laws the we set with light. What speed would be achieved of something just prior to hitting the singularity of a supermassive black hole?
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Gravity exists as the result of EM energy. All matter has this energy. The larger in mass and weight, the more energy, therefore larger objects of greater weight have a greater gravitational pull. The exception would be a collapsed star, with it's tremendous weight would have a greater pull than a larger object of less weight.
This follows the equation for energy (e=m/c sq). I feel that gravity or EM energy must travel at the speed of light to leave or enter dimensions hence the flash of light often reported in the past when things dissappear.
Now the force of gravity, different from it's speed, could vary based on the source and distance objects effected. Therefore gravitational force based on speed is also interdimentional. -
There is something fishy here! If you measure the direction of suns gravity it points to where the sun will be in 8 minutes. This sort of tells me that gravity is much faster!
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Itd be so nice if this was wrong. David Webber sci fi warfare implications on faster than light communications was awe inspiring (Honor Harington series gravity measurememts were instant.). It is worth noting that we dont have confirmed visual observations, however the grave wave testing teams are looking for collaboration.
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Im sure if we master gravity we can beat the speed of light.
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I guess when the sun burns out it would become a black hole. At that time would earth move away from its orbit around sun or would it fall into the black hole
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If you were running away at the speed of light from the Sun I guess you can't see the Sun. So if gravity propagates at the speed of light how the black hole can trap light?
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What's that thing in your hand that you keep clicking?
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I thought that as gravity is bending time and space, it will not be limited by space and so limited by maximum speed in space. So when Sun disappear it would instantly release all objects in Solar system.....
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If light can't escape from a black hole then gravity (which travels at the same speed) shouldn't escape either?
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You're theory doesn't hold up. Ever heard of something called aberration?
If gravity would propagate at c, the orbits of the planets (including Earth) would become so unstable that you would even notice a difference during a human lifespan. Do the math and in a few 100 years the orbit of the earth would be twice as far from the sun as it is today. And we know from our history books that this is not the case..
So: gravity moves MUCH faster than c, probably millions of times faster. -
If an asteroid was going to hit the Earth going like 40,000 mph would we see it before it hit? Example, like in the movie Deep Impact? I know it wouldn't take long to hit the ground but would it be visible?
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but what abaut black holes the grawity there sucks in even light , dosent that mean that gravity there is faster than speed of light ?
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