Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: steve on 24/04/2010 14:30:03
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steve asked the Naked Scientists:
If the sun were suddenly to disappear without a trace, would all the planets fly off their orbits simultaneously, or in order of closeness to the sun, i.e. Mercury first, then Venus etc.
What do you think?
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I obviously couldn't give you a text book answer or even a guaranteed correct one but I will try and offer an opinion.
The force with which the sun exerts on all the planets and orbiting bodies i.e asteroids is far greater than the force they all exert on each other. If the sun were to disappear then I would assume all the planets would carry on in their last point of trajectory (like if you cut the string sack of marbles they will at roll away in different directions.) Planets like mars and earth will exert certain forces on each other but not enough to bring them into orbiting each other as they are far apart. Jupiter and saturn may be able to pull certain bodies into orbit around them depending on whats close by. The general effect would be that the majority of the bodies would leave the solar system independantly of each other.
The effect would be instantaneous as gravity is the way in which the universe is bent and warped (according to Einstein's theory of relativity), thus changes happen faster than the speed of light.
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"The effect would be instantaneous as gravity is the way in which the universe is bent and warped (according to Einstein's theory of relativity), thus changes happen faster than the speed of light".
Nothing is instantaneous both theory and experiment show that the force of gravity propergates at the speed of light.
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See that's what gets me, if gravitational waves actually propagate at the speed of light then how do scientists offer one prediction that the universe may collapse on its self nearing the end as the amount of mass may have enough gravity to cause the universe to slow down or contract but how can the waves ever catch up as the universe is expanding faster than the speed of light?
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The problem with answering the question regarding whether planets would fly off instantaneously or after a time delay due to the speed of light limitation lies in the formulation of a question which has an impossible assertion; i.e. that the sun "suddenly" disappears. This can't happen. It could explode or somehow be moved away at finite speed but cannot disappear. From any normal event you can construct a model consistent with the physics. Anything that happens to the sun would propagate away from that event at the speed of light, whether a visual phenomena or some disturbance to its gravity field. I don't think you can formulate any viable solution for an event that has the sun "disappearing".
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How about a black hole swallows the sun. Although that's not instantaneous', crossing the event horizon can't take that long. Now what happens - all the planets fly off simultaneously or one at a time? How long does it take for space-time to 'unbend'?
Steve
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What if, what if, what if.....
I like the idea of infinity and the thinking that leads to probability actually being certainty as a result. So on that assumption lets assume that the question Steve asks leads to some spatial butterfly effect and that a rift in the fabric of spacetime opens up, swallows the sun and closes again in an eyeblink. Do we actually have unequivocal evidence that the resulting missing gravity well would take the 8 minutes or so that light takes to reach Earth to show it effects?
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Yes
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The problem with the black hole idea is it would have a different effect, instead of there being no gravitational force with the sun disappearing it would be the gravity of the black hole plus the sun. Things would be more interesting then with the increased gravity and a definite change in the orbits of all the bodies, although they would not be sucked in like the movies as a black hole does not actually suck things in. Although for the original idea of the sun just disappearing, well I think my original idea was a good approximation although I was wrong about the speed of gravity waves so a slight adjustment would be that each body would shoot off in its own trajectory one after the other with the earth happening about 8 minutes later.
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My question is more of a thought experiment about the nature of gravity. What is the evidence that the "missing gravity well would take the 8 minutes or so that light takes to reach Earth to show its effects",implied by Soul Surfer's 'Yes' to quibitheed's question. Black holes bend space-time completely around so there is no escaping mass, light or radiation (excepting Hawking radiation). What about gravity? If gravity is just how space-time bends and black holes bend it completely, how do they suck in nearby matter or speed up stellar orbits? Their gravity must extend beyond the event horizon which means gravity behaves differently than photons. And this implies gravity is not particle mediated (graviton) or wave mediated(gravity wave). Doesn't that knock out the speed of light limit? Which means either gravity is instantaneous and all the plants would fly off their orbits simultaneously (not withstanding interplanetary gravitational effects)or the planets fly off one by one, nearest first,which means there is a "speed of gravity" which is not necessarily equal to the speed of light. Your thoughts?
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A black hole may prevent photons "escaping" but that does not affect the static field - a charged black hole would still have an electric field. It also has a gravitational field. You cannot have objects magically disappearing and expect to reason a sensible answer consistent with the laws of physics. If a charged object appears or disappears (black hole or not) it would have to cause a change in the associated field which would ripple away at light speed. In practice, you have to move your charge in or out at a permissable rate. The same would be true of a gravity field I think. Any change to the shape of the curvature of space-time would be the result of matter and that can only move within the constraints of relativity.
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steve asked the Naked Scientists:
If the sun were suddenly to disappear without a trace, would all the planets fly off their orbits simultaneously, or in order of closeness to the sun, i.e. Mercury first, then Venus etc.
The second you wrote. Gravity perturbations propagate at the speed of light.
Laconic answer because during the years we have already discussed deeply the subject.
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The problem with answering the question regarding whether planets would fly off instantaneously or after a time delay due to the speed of light limitation lies in the formulation of a question which has an impossible assertion; i.e. that the sun "suddenly" disappears. This can't happen. It could explode or somehow be moved away at finite speed but cannot disappear. From any normal event you can construct a model consistent with the physics. Anything that happens to the sun would propagate away from that event at the speed of light, whether a visual phenomena or some disturbance to its gravity field. I don't think you can formulate any viable solution for an event that has the sun "disappearing".
This answer is correct. Unfortunately, simply making the Sun disappear is not compatible with the known laws of physics, and as a consequence physics doesn't give a definitive answer as to what would happen next.
It's certainly true to say, however, that it is the Sun's influence that keeps the solar system 'glued' together; without it, the planets could not carry on orbiting. (But then they wouldn't ever have formed in the first place, either.)
How about a black hole swallows the sun. Although that's not instantaneous', crossing the event horizon can't take that long. Now what happens - all the planets fly off simultaneously or one at a time? How long does it take for space-time to 'unbend'?
Steve
If the Sun were to collapse into a black hole, the planets would keep on orbiting the black hole. From a distance, the strength of gravity is only sensitive to the total amount of mass, not to what particular form that mass is in.
Monthly astronomy podcasts - www.thenakedscientists.com/astronomy
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If the Sun were to collapse into a black hole, the planets would keep on orbiting the black hole. From a distance, the strength of gravity is only sensitive to the total amount of mass, not to what particular form that mass is in.
Monthly astronomy podcasts - www.thenakedscientists.com/astronomy
If we could (somehow) continue to provide energy to keep the world, light and warm, and feed ourselves (I realise it's a big if) - is there any reason why we could not continue to survive orbitting a black hole which had a similar mass to that of the sun?
Matthew
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If we could (somehow) continue to provide energy to keep the world, light and warm, and feed ourselves (I realise it's a big if) - is there any reason why we could not continue to survive orbitting a black hole which had a similar mass to that of the sun?
Matthew
Yep, so long as we could find some way to keep the world warm and grow crops, we could survive on a planet orbiting a black hole!
Monthly astronomy podcasts - www.thenakedscientists.com/astronomy
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A non realistic scenario of the EVENT that gives food for thought… Removing the Sun from existence, like plucking a feather off a dead chicken! This is similar to what Nicolas Copernicus did by changing the sun’s location relative to earth, being the center of all our planetary system.
Let’s take in consideration the position of all the planets relative to each other. Then look at their position within their orbit around the sun at the time of the event. Do not forget any other debris in the solar system which may be attracted to any one of the stellar bodies due to the lack of the sun’s gravity.
All the previously orbiting bodies, relative to their angular acceleration towards the sun by the sun’s gravity, is now being absent, slingshots these bodies to a linear path and their instantaneous velocity is at that moment of the event.
Providing they are not influenced by any other masses that can affect their individual gravity and attraction, Newton says they will continue in a straight line at a constant speed.
Now the moons, of these individual bodies as the polar revolutions of the planets may have a small effect and provide an off balance and provide a wobble or an eccentricity to their linear velocity, like a poorly balanced wheels this will depend on their relative mass ratio between each other. These events may become catastrophic in time and cause them to break apart from their own mass or get sucked in, to create a new mass or an opposite resultant.
Similar to the ancient dual balled ends type slingshots, an off beat axes revolving in flight.
Jupiter, being the biggest having the most mass, may have the influence to attract these bodies sucking them in or providing a center axes to new system's orbiting orientation for our planets. Since we may now have a scenario picked, because balance is needed to sustain, what other objects will this system affect or affect this system? The scenario is as infinite as time and space itself. If man can dream it, it can become reality. All is missing in the formula is the constant variable, which is time. ∫[4ƒx(Α→Ω)/ƒ(α→ω)] let x=(1/∞)=t<[1/(0)]
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Does black holes (maybe the rotating ones)not emit streams of radiation like a pulsar and hence not be healthy to be close to? Also what about the tidal forces that the black hole would emit on the orbiting bodies? Would that also not be very healthy?
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I believe the emitting jets of radiation are 180 from each other and is aprox 90 deg from the event horizon. Sort of like squeezing a bannana out of it's skin.
The tidal wave force? I do not think it would emit but it may attract. I would think that at the orbiting accecleration reaching light speed, well if one has a death wish just getting that close will kill. Yepper not healthy at all! The Angle Hair Pasta theory!