/sci/ - Science & Math

[Anonymous No.5829198]

If I'm correct in thinking, doesn't the effects of gravity travel faster than the speed of light ?

If the universe consisted of nothing but two solar masses 1 light year apart.

Then surely gravity would begin pulling them together the very second they came into being, while it would take year for light from one star to reach the other...

[Anonymous No.5829203]

>>5829198
>doesn't the effects of gravity travel faster than the speed of light ?
It doesn't.

[Anonymous No.5829202]

Nope, speed of light. This is measurable to several decimal places. Sorry, can't build a gravity-powered ftl communication device.

[Anonymous No.5831140]

>>5829203
But then if the gravitational force is due to the interaction of virtual gravitons how does gravity escape a black hole?

[Anonymous No.5831146]

>>5831140
gravitons aren't affected by gravity, they simply carry the force.

[Anonymous No.5831192]

>>5829198
this is wrong... if you would remove the sun from the solar system, for 8 minutes we would still have light AND the earth would orbit a now non-existing star

'gravity' travels at the speed of light

[Anonymous No.5831204]

>>5831140
Why would they be constrained by it? They're virtual particles. And virtual particles communicate instantaneously. Virtual photons, gravitons, gluons, and W/Z bosons communicate their interactions instantaneously. However, obviously Electroweak, Strong, and Gravitational effects propagate at the speed of light.

[Anonymous No.5831226]

Gravity propagates at the speed of light op, but it's effects are felt 'as if' it traveled instantaneously, for example the earth is pulled by gravity form the suns current position not where the source of light appears to be 8 min ago

[Anonymous No.5831236]

>>5831226
This is FALSE, you fucking idiot. You even contradicted yourself in your own sentence.

Gravity propagates at the speed of light. In absolute time as measured by a distant observer, the earth is influenced by the Sun's position 8 minutes ago.

Otherwise you could transmit information faster than the speed of light, and causality would be undefined

[Anonymous No.5831256]

>>5831236
>This is FALSE, you fucking idiot
no it is not false.

>You even contradicted yourself in your own sentence.
No there is no contradiction

>the earth is influenced by the Sun's position 8 minutes ago.

nope sorry that is wrong

>Otherwise you could transmit information faster than the speed of light, and causality would be undefined
nope sorry that is also false, you cannot use gravity to transmit infomration faster than teh speed of light, becasue gravity propagates at the speed of light, but it's affects are still felt as if it was acting instantly form the mass' current position.. this is baby tier astronomy stuff here kid

if this is confusing to you.. imagine the gravitational field as moving and not a static propagation from a single point like light.

[Anonymous No.5831259]

>>5831256
God damn you're retarded, you can't spell correctly and you're spouting utter nonsense.

Gravity propagates at the speed of light.

>>5831204
No, photons still travel through space, gravity bends space so that it is not Euclidean. Gravitons would still have to travel through space, so they would be effected by the curvature of spacetime. It's one of the major reasons gravity is irreconcilable with the standard model.

[Anonymous No.5831267]

>>5831259
Kid you should at least read wikipedia before spouting of nonsense.

"The consequence of this is that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay that is due to any "signal" traveling (or propagating) from the charge, over a distance to an observer"

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

>protip.. nasa uses instantaneous Newtonian gravity model for planning spaceflight.

[Anonymous No.5831268]

>>5831256
>idiotic words

You're absolutely, painfully wrong. If gravity propagates at the speed of light, then how the fuck would the Earth experience the sun's INSTANTANEOUS position? Answer: it wouldn't.

If the sun were to vanish, the planets would continue to orbit the sun's former location for several minutes, before this information propagated to them. In the Earth's case, it'd take ~8 minutes. For 8 minutes, even though the sun didn't exist anymore (as measured by a distant, comoving observer) the Earth would still be illuminated by sunlight, and would still centripetally orbit the former star.

>becasue gravity propagates at the speed of light, but it's affects are still felt as if it was acting instantly form the mass' current position
These are contradictory statements. The effect of the sun's mass IS GRAVITY, you stupid shit. learn2physics and learn2english

We APPEAR to see the sun's current position and brightness, but that's not the case. Light and gravity travel at a finite speed. For all we know, the Sun could have literally vanished between now and 8 minutes ago.

What we experience is NOT the sun's current status, but it's status time-delayed by the finite speed of light. This is true of every star in the universe. The furthest stars are some 13 billion years before us, and we see them and experience their gravity as of their status 13 billion years ago.

This isn't even GR. This is the very essence special relativity, which you obviously never took.

[Anonymous No.5831272]

>>5831267
>static fields
static fields you fucktard, meaning no change in time.

[Anonymous No.5831276]

>>5831259
>Gravity propagates at the speed of light.
Correct, in the face of that one's utter stupidity.

> No, photons still travel through space, gravity bends space so that it is not Euclidean. Gravitons would still have to travel through space, so they would be effected by the curvature of spacetime.
We are talking about virtual photons and virtual gravitons, dicktard. The ones in Feynman diagrams. They travel instantaneously, and are lords unto themselves. You're thinking of real photons and gravitons (like energy emissions from quantum transitions). Those travel at the speed of light, and follow the geodesics of the local spacetime metric.

>It's one of the major reasons gravity is irreconcilable with the standard model.
Absolutely false. Please read this: http://arxiv.org/pdf/gr-qc/0004005v1.pdf
for the correct reasons.

[Anonymous No.5831281]

>>5831272
>>5831268
I'm afraid you are just confused.. if you learn more about gravity you will start to understand yes gravity propagates at the speed few light, but prorogation does not limit it's affects fro radiating form the current position of a mass, because the gravitational field and the mass are both moving. Not one or the other by itself.

"The finite speed of gravitational interaction in general relativity does not to lead to the sorts of problems with the aberration of gravity that Newton was originally concerned with, because there is no such aberration in static field effects. Because the acceleration of the Earth with regard to the Sun is small (meaning, to a good approximation, the two bodies can be regarded as traveling in straight lines past each other with unchanging velocity), the orbital results calculated by general relativity are the same as those of Newtonian gravity with instantaneous action at a distance"

[Anonymous No.5831282]

>>5831192
>>5831204
>>5831236
>>5831259
>>5831268
>>5831276
Y'all are correct, despite others' sheer stupidity and inability to comprehend the difference between static and dynamic fields.

>>5831226
>>5831256
>>5831267
kill yourselves

[Anonymous No.5831290]

>>5831282
Properties of Gravity

Gravity has some curious properties. One of them is that its effect on a body is apparently completely independent of the mass of the affected body. As a result, heavy and light bodies fall in a gravitational field with equal acceleration. Another is the seemingly infinite range of gravitational force. Truly infinite range is not possible for forces conveyed by carriers of finite size and speed -- a point we will elaborate in Part II.

Another curious property of gravity is its apparently instantaneous action. By way of contrast, light from the Sun requires about 500 seconds to travel to the Earth. So when it arrives, we see the Sun in the sky in the position it actually occupied 500 seconds ago rather than in its present position. (Figure 1.) This difference amounts to about 20 seconds of arc, a large and noticeable amount to astronomers.

From our perspective, the Earth is standing still and the Sun is moving. So it seems natural that we see the Sun where it was 500 seconds ago, when it emitted the light now arriving. From the Sun's perspective, the Earth is moving. It's orbital speed is about 10-4 c, where c is the speed of light. So light from the Sun strikes the Earth from a slightly forward angle because the Earth tends to "run into" the light. The forward angle is 10-4 radians (the ratio of Earth's speed to light speed), which is 20 arc seconds, the same displacement angle as in the first perspective. This displacement angle is called aberration, and it is due entirely to the finite speed of light. Note that aberration is a classical effect, not a relativistic one. Frame contraction and time dilation effects are four orders of magnitude smaller, since they are proportional to the square of the ratio of speeds.

[Anonymous No.5831292]

>>5831282
Now we naturally expect that gravity should behave similarly to light. Viewing gravity as a force that propagates from Sun to Earth, the Sun's gravity should appear to emanate from the position the Sun occupied when the gravity now arriving left the Sun. From the Sun's perspective, the Earth should "run into" the gravitational force, making it appear to come from a slightly forward angle equal to the ratio of the Earth's orbital speed to the speed of gravity propagation.

This slightly forward angle will tend to accelerate the Earth, since it is an attractive force that does not depend on the mass of the affected body. Such an effect is observed in the case of the pressure of sunlight, which of course does depend on the mass of the affected body. The slightly forward angle for the arrival of light produces a deceleration of the bodies it impacts, since light pressure is a repulsive force. Bodies small enough to notice, such as dust particles, tend to spiral into the Sun as a consequence of this deceleration, which in turn is caused by the finite speed of light. This whole process is called the Poynting-Robertson effect.

But observations indicate that none of this happens in the case of gravity! There is no detectable delay for the propagation of gravity from Sun to Earth. The direction of the Sun's gravitational force is toward its true, instantaneous position, not toward a retarded position, to the full accuracy of observations. And no perceptible change in the Earth's mean orbital speed has yet been detected, even though the effect of a finite speed of gravity is cumulative over time. Gravity has no perceptible aberration, and no Poynting-Robertson effect -- the primary indicators of its propagation speed. Indeed, Newtonian gravity explicitly assumes that gravity propagates with infinite speed.

[Anonymous No.5831295]

>>5831281
Don't assume you know more about gravity than me. You're wrong. lrn2spell, faggot

You also missed the point of this discussion entirely. We're not talking about observer effects on static fields. We're talking about dynamic fields. Like the Sun *magically* disappearing, or SIGNIFICANTLY moving. You wouldn't notice for 8 minutes.

Otherwise, in principle, I could take a heavy Mass, and move it back and forth to transmit a message. And if the gravitational field at YOUR location depended on my Mass's instantaneous position (rather than propagation-delayed position), then you could receive messages instantaneously, i.e. faster-than-light.

You are confused, and stupid (or young) enough not to realize it.

[Anonymous No.5831302]

>>5831295
>You wouldn't notice for 8 minutes.
Yes it's true that you would not notice for 8 minutes if it disappeared.

>And if the gravitational field at YOUR location depended on my Mass's instantaneous position (rather than propagation-delayed position), then you could receive messages instantaneously, i.e. faster-than-light.

yes everything you guys are saying is correct, In fact I am not disagreeing with anything said in this thread, but here is what you are missing.. say the sun was traveling "left to your current position at 1,000,000 mph, then suddenly started traveling right at 1,000,000 mph.. well you would still detect the sun moving left at 1,000,000 mph for as long as it took the gravitational waves to reach you, you would feel the suns gravity from a position it never reached! While it was traveling in the other direction, until it's new wave came from the travel to the right at the speed of light.

[Anonymous No.5831303]

>>5831290
>gravity is independent of mass
yeah, except you are totally wrong.

g = G*m1*m2/r^2

the whole thing about two objects of different falling at the same speed is only an approximation, because the earths mass >> the mass of either of the two objects.

technically, in a vacuum and with unbelievably high precision instruments, the larger mass would be seen to accelerate towards the earth faster.

[Anonymous No.5831305]

>>5831303
where g is the gravitational acceleration felt between the bodies, G is the gravitational constant, r is the distance between the two bodies, and m1,2 are the masses of the respective bodies.

[Anonymous No.5831310]

>>5831302
>you would feel the suns gravity from a position it never reached!

no you wouldnt. you will always feel the suns true position, just 8 minutes after it was there. if the sun is moving left and then stops, and moves right, you will feel it move left, stop, and then move right, 8 minutes after it had done so.

stop outsmarting yourself, you need something more challenging than that.

[Anonymous No.5831311]

>>5831303
Nigga you better be trolling or it's time to redo highschool

[Anonymous No.5831315]

>>5831311
google it. bachelors in engineering physics, masters in nanotech.

Or if you knew how to do math, you would see immediately that I am correct. Equal acceleration of two different masses on earth is an approximative effect.

If m1 is mass of the earth and m1 >> m2 (or m3), then the equation reduces to:

g = G*m1/r2

at which point the acceleration is independent of the mass of the falling object, and dependent only on the mass of the earth, instead.. which is gallileo's discovery.

[Anonymous No.5831316]

>>5831315
even then, making a blanket statement that "gravity is independent of mass' is just undeniably wrong on all counts.

[Anonymous No.5831321]

>>5831311
itt: retards who think they are smarter than actual physics majors.

too bad you stopped with highschool, anon

[Anonymous No.5831349]

>>5831140
>how does gravity escape gravity?

[Anonymous No.5831432]

>>5831315
It's the acceleration that's independent, because:

G * Mz*m/r^2 = ma, so:

a = G Mz/r^2

[Anonymous No.5831443]

>>5831146
Nope, gravitons couple to gravitons.
I've heard of people modelling gravitons as pairs of gluons, and it's well known that gluons will scatter gluons.
>>5831140
>virtual gravitons
>virtual

[Anonymous No.5831444]

>>5831311
>>Can't into basic highschool physics yet insults others about it

[Anonymous No.5831497]

>>5831315
You are correct, but for all the wrong reasons [the force equation does not simplify in the manner you are describing]. The reason it works out is because the falling objects do not exert sufficient force on the Earth to cause noticeable acceleration and thus the Earth acts as a fixed reference frame. If you were to do this with several similarly sized objects well outside the influence of other objects, then their acceleration would be more complicated as a result of both objects undergoing measurable acceleration due to the gravitational field of the other.

[Anonymous No.5831501]

>>5831443
Given that interactions are mediated by exchange of virtual particles, I don't really see what you are saying.

[Anonymous No.5831505]

>>5831302
this guy is so unbelievably wrong.
>>5831310
correct

[Anonymous No.5831539]

>>5831290
>that picture
>what is relativity

[Anonymous No.5831542]

The speed of gravity has not been measured to any reasonable accuracy, all experiments that claimed to have done so were shown to be roundabout ways of measuring the speed of light

[Anonymous No.5831544]

>>5831349
>Doesn't know what black holes are

[Anonymous No.5831546]

>>5831544
Gravity isn't something that affect itself.

[Anonymous No.5831550]

>>5831546
>Still doesn't know what black holes are

[Anonymous No.5831565]

I'm sorry to interrupt this argument, guys, but gravitons don't exist. That's the undeniable truth. We've managed to track down even the Higgs Boson, but the graviton is still beyond our reach- despite its certain prevalence on Earth. There's simply no empirical evidence for its existence, so we have to turn to other solutions. Could we have massively misunderstood gravity?

Unfortunately, yes. Professor Erik Verlinde managed to derive the laws of gravitation from the laws of thermodynamics, displaying that it could, indeed, be an entropic force without need for a subatomic particle. With this explanation, indeed, the necessity of dark matter and dark energy is brought into doubt. This is the clear model that we need to be investigating. It's reductionist and mathematically sound - two key aspects of great scientific theories.

So I'm sorry, everyone, but you're all wrong. It's just entropy,

[Anonymous No.5831575]

>>5831501
Virtual particles are not bound to move slower than the speed of light.

[Anonymous No.5831578]

>>5831546
Yes it does. That's why the EFEs are highly non-linear.
Gravity is caused by energy, and gravitational fields contain energy. Gravity causes more gravity, and this is why the sum of two solutions to the EFEs isn't, in general, another solution.

[Anonymous No.5831583]

I'm always thinking about questions correlating to gravity, here's my most recent i'm hoping someone with more knowledge on physics than I can explain to me: Can empty space inbthe universe be the direct result of gravity itself?

[Anonymous No.5831584]

>>5831565
http://en.wikipedia.org/wiki/Graviton#Experimental_observation

We will never find gravitons directly. That doesn't mean they don't exist - if they existed with exactly the predicted properties, we would never be able to find them.
We need to look for indirect evidence.
I'm still doubtful of their existence, but a lack of direct experimental evidence is exactly what we'd detect if they were real.

[Anonymous No.5831590]

gravity is caused by quantum entanglement you don't have to be a highlight to see that

[Anonymous No.5831592]

>>5831583
>noko
>2013
Entropic gravity ftw btw

[Anonymous No.5832155]

>>5831303
no, G*m1*m2/r^2 is the formula for the gravitational force, not the gravitational acceleration

[Anonymous No.5832197]

>>5831575
And yet all the forces which they transmit are restrained to slower than light transmission.