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Question about gravity

Tumbleweed said:
Put an Existence Switch on the sun and flip it off. It takes several minutes for it to go dark on Earth, right?
BUT- does the Earth immediately spin out of orbit or does it wait until things get dark
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Fredrik said:
This question was answered earlier in this thread.
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Tumbleweed said:
Oh I know the answer: The Earth would indeed immediately spin out of orbit
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Is that the answer you found earlier in this thread? How hard can it be to go through a few pages looking for the answer? If you can't be bothered to do that, then why should anyone bother replying to you?
 
ponderingturtle said:
So things propagating at C is the one thing every reference frame can agree on.
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We got a decent treatment of SR in my sophomore year, but I didn't have room for the GR/intro to cosmology course. Moreover, that class (from what I'm told) doesn't get much into String Theory. That seems to be left for grad studies in my dept.

So anyway, I was just wondering if there was some sort of neato cosmology trick thingy that I didn't know about which would somehow allow for 'instantaneous' gravity effects...
 
Jimbo07 said:
So anyway, I was just wondering if there was some sort of neato cosmology trick thingy that I didn't know about which would somehow allow for 'instantaneous' gravity effects...
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There's not, but the question of causality in gravity is actually a very tricky one. If you allow strange sources of energy you can easily end up with spaces in which it's possible to travel along a closed loop in time. That's bad - very bad! - so most people think those strange energy sources don't exist. But actually no one has ever managed to prove that such a thing is impossible with normal energy sources.

Still, at least locally the cone of influence of gravity (and everything else) is always identical to what it would be for light in flat space.
 
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The trouble with things like an "existence switch" on the Sun is that it falls foul of the First Law of Thought Experiments, which says that if you have to break the laws of physics to perform the experiment, it won't tell you anything about reality. This is probably most commonly seen when people come up with questions like "What would happen if you spun a perfectly rigid rod so that the end was moving faster than light?". The answer is that there is no such thing as a perfectly rigid rod, so the question is irrelevant.

Asking what would happen if the Sun, or any object, suddenly disappeared is the same. The answer is "The Sun can't suddenly disappear.". Even the usual answer as given by Sol Invictus doesn't really make sense. Sure, we can say that there wouldn't be an instantaneous effect because we know nothing propagates faster than light, but it still doesn't actually mean anything because it isn't possible for it to happen. Mass can move, and the effects of the movement propagate at the speed of light, but the whole process is always continuous, with existing matter and energy changing but never appearing or disappearing.
 
Cuddles said:
Asking what would happen if the Sun, or any object, suddenly disappeared is the same. The answer is "The Sun can't suddenly disappear.". Even the usual answer as given by Sol Invictus doesn't really make sense. Sure, we can say that there wouldn't be an instantaneous effect because we know nothing propagates faster than light, but it still doesn't actually mean anything because it isn't possible for it to happen. Mass can move, and the effects of the movement propagate at the speed of light, but the whole process is always continuous, with existing matter and energy changing but never appearing or disappearing.
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That's true, and it's a good point. It's better to modify the question a little - you can ask, what would happen if the sun suddenly accelerated like crazy and flew off in some direction at high speed (which doesn't violate any laws - it might have had a giant heat-proof rocket attached to it).

But the point is that no matter what physical situation you concoct, no influence ever propagates faster than light (at least locally).
 
sol invictus said:
That's true, and it's a good point. It's better to modify the question a little - you can ask, what would happen if the sun suddenly accelerated like crazy and flew off in some direction at high speed (which doesn't violate any laws - it might have had a giant heat-proof rocket attached to it).

But the point is that no matter what physical situation you concoct, no influence ever propagates faster than light (at least locally).
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I am happy with my relativity of simultaneity answer.
 
Tumbleweed said:
A good background in sub atomic particles ( that I don't have) would have been very helpful, but I grasped the basic concepts they were getting at: that various and sundry types of vibrating and spinning strings make up the four fundamental forces of nature, and that one may be tranformed into another by, basically plucking the strings. Photons are considered electromagnetism's string, gravitons, gravity's, and I forget the ones for the weak and strong nuclear forces. Boson?
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A basic primer for sub atomic particles and a couple of links for those willing to educate themselves.


Boson – A particle with integer spin or some whole number (1, 2 ,3…, -1, -2, -3…). These particles obey Bose-Einstein statistics and do not obey the Pauli Exclusion Principle

Fermions – Particles with half integer spin or some whole number plus 0.5 (1.5, 2.5, 3.5…, -1.5, -2.5, -3.5…). These particles obey Fermi-Dirac statistics and obey the Pauli Exclusion Principle


http://en.wikipedia.org/wiki/Boson

Particles composed of a number of other particles (such as protons, neutrons or nuclei) can be either fermions or bosons, depending on their total spin.
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Lepton – Bosons or Fermions that do not interact via the strong nuclear force or only interact via the electromagnetic and weak nuclear forces. The Electron is a Fermion and a Lepton. The Proton and the Neutron are also Fermions but not Leptons as they also interact via the strong nuclear force.

Photon- A Boson and Lepton that mediates the electromagnetic force.

Gluon- A Boson that mediates the strong nuclear force

Intermediate Vector Boson- A Boson which mediates the weak nuclear force, the weak nuclear force and electromagnetism are combined under electroweak theory

Higgs particle- a theoretical Boson that is proposed to be responsible for mass (based on Electroweak theory).

Graviton- a theoretical Boson that is proposed to mediate the gravitational force

For a more complete list and explanation of particles


http://en.wikipedia.org/wiki/List_of_particles


An interesting coincidence of science and language is that all of the force mediating particles (or the particles tying things together) are Bosons, due to their integer spin. On a ship the warrant officer in charge of the rigging, anchors, cables, and the deck crew is the Boatswain or "Bosun", although that officers “total spin” is not considered.
 
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The Man said:
Lepton – Bosons or Fermions that do not interact via the strong nuclear force or only interact via the electromagnetic and weak nuclear forces. The Electron is a Fermion and a Lepton. The Proton and the Neutron are also Fermions but not Leptons as they also interact via the strong nuclear force.

Photon- A Boson and Lepton that mediates the electromagnetic force.
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There's a minor error in terminology here - all leptons are fermions. There are six of them - electron, muon, and tau, each with its respective neutrino. Photons and other gauge bosons are not leptons.

Also, if you wanted to make a full list of all the known elementary particles, you need to add the quarks.
 
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sol invictus said:
There's a minor error in terminology here - all leptons are fermions. There are six of them - electron, muon, and tau, each with its respective neutrino. Photons and other gauge bosons are not leptons.

Also, if you wanted to make a full list of all the known elementary particles, you need to add the quarks.
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Correct, that was my mistake. Although Photons mediate the electromagnetic force they are not charged and do not interact via the electromagnetic force so are not Leptons.

I really did not want to make a complete particle list including all the Hadrons (Baryons and Mesons) but I should have at least mentioned the quark if not mentioning all the types of quarks that make up all the different Hadrons.

Another omission on my part is that I failed to mention that all of these particles interact via the gravitational force, which can lead to some problems when considering a theoretical mediating particle such as the graviton.
 
Picture two fruit sellers in the not so distant past. The first one measures using kilograms, the second has a scale using grams. The second seller, using grams, has more selling options but takes more time since the units he is working with are smaller. Likewise, the first seller, using kilograms, has fewer selling options but is quicker. Even though the second seller has more precision than the first, it doesn't make the first seller "wrong" in any way. In fact his way in this case is faster.

This analogy closely relates to the Newton/Einstein argument taking up a large chunk of this thread.
 
Not really. Parts of the discussion can be described like that, but Robinson claimed that many scientific laws have been proven to be exactly true (yeah, right), and that people who don't understand that are ignorant, stupid or crazy.
 
Fredrik said:
Not really. Parts of the discussion can be described like that, but Robinson claimed that many scientific laws have been proven to be exactly true (yeah, right), and that people who don't understand that are ignorant, stupid or crazy.
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Nobody said anything like that, except for you, just now in your post. Making up stuff will not help your case. Providing real scientific articles, papers or studies will.
 
robinson said:
Nobody said anything like that, except for you, just now in your post. Making up stuff will not help your case. Providing real scientific articles, papers or studies will.
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It would, except that when we provided them you ignored them. Since you're also the only one that doesn't understand this, there's no point.

Sorry.
 
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I understand that you and a few others think you can define words, and you disagree with the vast body of scientist about what words mean, and how they are used. Repeating yourself without a shred of evidence does not improve your position. But don't stop, it is amusing.

Now about Gravity ...
 
Jimbo07 said:
Is this correct? I thought gravitic "information" also travelled no faster than c.

I know no cosmology...

:(
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You are likely thinking of what are referred to as "gravitational waves" - these are a consequence of Einstein's theory of general relativity. They are predicted to travel at the velocity of light (c) and are generated during, pardon the pun, massive disruptions in space-time such as two neutron stars or black holes colliding and merging. Here's more info...

http://en.wikipedia.org/wiki/Gravitational_waves

To my knowledge, gravity waves haven't yet been detected. This is one aspect of GR which hasn't yet been tested, though there are experiments (most famously LIGO) in the works to check it out...

http://en.wikipedia.org/wiki/LIGO

Cheers - Mattus
 
MattusMaximus said:
You are likely thinking of what are referred to as "gravitational waves" - these are a consequence of Einstein's theory of general relativity. They are predicted to travel at the velocity of light (c) and are generated during, pardon the pun, massive disruptions in space-time such as two neutron stars or black holes colliding and merging. Here's more info...

http://en.wikipedia.org/wiki/Gravitational_waves

To my knowledge, gravity waves haven't yet been detected. This is one aspect of GR which hasn't yet been tested, though there are experiments (most famously LIGO) in the works to check it out...

http://en.wikipedia.org/wiki/LIGO

Cheers - Mattus
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Actually, I think jimbo was right (Tumblehome was wrong). You're also right about gravitational waves, of course, but gravitational "information" also goes no faster than c.
 
robinson said:
Nobody said anything like that, except for you, just now in your post. Making up stuff will not help your case. Providing real scientific articles, papers or studies will.
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So would you care to comment on the fact that I provided a quote and link about how the inverse square law as false something you claimed no one else had ever claimed before?
 
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