# Infinitesimal gravitation pull

1. Oct 9, 2004

### Zuryn

If you have two particles that are even billions of light years away from each other, is there any gravitational pull between then? (Considering the possibility that there is nothing else in the universe)

2. Oct 9, 2004

### arildno

There's no evidence to the contrary..

3. Oct 9, 2004

### Tide

Yes, the attraction would be minuscule though not infinitesimal in the strict mathematical sense! Newton's Law of Gravitation, however, would have to be modified over such long distances since it doesn't take into account the finite time required for one object to know about changes in the other.

4. Oct 9, 2004

### Rocko

my understanding

ah yes but does it take a finite time for that object to know about the other? cause if it did then i would assume they would no longer be a billion light years apart correct? what i mean is the particle, photon whatever will have travelled at lightspeed to the other.

Last edited: Oct 9, 2004
5. Oct 10, 2004

### rcgldr

So if a particle changes (like annihilated), how fast does the change in gravtation field move, or how long before the remaining particle no longer experiences the gravitation field it once experienced?

What about the other forces, say like magnetic, the weak, or the strong force, if there is a change, what is the "speed" of the change in the field?

6. Oct 10, 2004

### Nereid

Staff Emeritus
First, it's very difficult to think of a situation in which, even in principle, the 'source' of a gravitational field 'disappeared' (or 'appeared'); for example, in GR, an annihilation event doesn't result in a loss of 'space-time curving stuff', just a change in its form (two, or more?, photons instead of two - or more? - particles).

Second, all forces carried by massless 'force carriers' 'propogate' (or 'travel') at c; this includes EM and the strong force. In GR, gravity also 'propogates' at c; a consistent 'force carrier' view of gravity posits the 'graviton', which would be massless. The weak force carriers (Z and W particles) are anything but massless, so this force doesn't propogate at c. Note that the weak and strong forces are short-range forces, so it would be quite difficult to directly test their 'propogation speed' experimentally; indirectly we could conclude that as there are no good experimental or observational results inconsistent with QCD and the electro-weak theory (theories?), and as these theories predict c as the propogation speed, we could say that 'experiments are consistent with c being the speed of propogation of the strong field'.

7. Oct 10, 2004

### Rocko

Ok, i am thinking about some basic experiments i have read about like the double slit experiment where the interference pattern cause buy 1 photon suggests that that photon is in 2 positions at the same time. This being true the time for it to get from say A to B to me seems to be zero. Another phenomenon i remember way back from first year chem was the idea of the electron shell and its probability orbital, i mean they can predict with fairly accurate reliabilty where that electron may be but never 100%. So it is possible that it could be a billion light years away from its own nucleus just not probable. And what about anti particles same thing if my anti particles where destroyed on the other side of the universe then would i not also be simultaneously destroyed?

8. Oct 10, 2004

### cepheid

Staff Emeritus
What??? There are no anti-particles specific to you that could be called "your" anti-particles! There are anti-protons, and anti-electrons (i.e. positrons) etc. If a subatomic particle comes into contact with it's antimatter counterpart, they will be mutually annihilated. Furthermore, if you come into contact with any antimatter in any form, I think you would probably be annihilated. But there is no "anti-Rocko" somewhere on the other side of the universe who is mystically tied to you so that if he is destroyed, so are you, no matter how far apart you are.

However, there was a whole episode of Star Trek (the original series) based on this misconception. Anyone remember that one?

Last edited: Oct 10, 2004
9. Oct 10, 2004

### Rocko

oh i certain realize there is no anti-Rocko in all probability its still just probability, there are anti-particulates of me somewhere, no? they just have not all conglomerated to make a negative of myself. However this is not my point. I was merely tryin to get clear what an idea of simultaniety really is and if it constitutes faster than light speed information exchange (events).

10. Oct 10, 2004

### cepheid

Staff Emeritus
NO

What did I say before? Particles are just particles...protons, electrons, etc. and their antimatter counterparts. For instance, if something were to destroy you, leaving nothing but your constituent atoms, there would (unfortunately) be nothing about them that would indicate that the particles came from you, and not from something else. They would be no different from any other atoms of the same elements in the universe.

To answer the second part of your question. Instantaneous transmission of information, or even faster than light transmission of information is impossible. No information can be transmitted faster than the speed of light. For instance, if the sun were to somehow magically disappear, the earth would nevertheless continue in it's elliptical orbit for another eight minutes, because the sun is a distance of eight light minutes from us. That's how long it would take before we perceived any change in gravitational effects.

To answer the first part, even simultaneity is not as simple as it first appears. Simultaneity is relative. Events that appear simultaneous to one observer may not appear simultaneous to another observer if the two are in relative motion. This is a consequence of the Special Theory of Relativity.

11. Oct 13, 2004

### Zuryn

What if, no matter the distance, gravity will exist?

12. Oct 15, 2004

### LURCH

Weather or not these antiparticles exist is not known for certain, but the evidence seems to be pointing toward "no". You are correct in claiming that they had to exist at some point in time, because the creation of any particle (according to all theory and observation so far) results in the creation of an anti-particle. So, when the particles that comprise you were first created, an equal mass of anti-particles also came into existance. For every electron in your body, a positron nust have been created at some time.

This has long been one of the great mysteries of particle physics, as well as Cosmology, because there should be an equal amount of matter and anti-matter in the universe, and we just don't see the anti-matter anywhere. Some theories propose that antimatter's shorter lifespan ahs resulted in the atrition of nearly all antiparticles in the universe, while soem say that the antimatter is out there, and we just don't see it, while another suggests that matter and antimatter can be created assymetrically, and for we haven't seen it happen yet, because it takes billions of "creation events" (I just invented that term) to see one in which matter is created without an accompanying antimatter. Thsi latter is especially itneresting as it implies that the Big Bang generated nearly equal, but not exactly equal amounts of matter and antimatter particles, like for every hundred billion antimatter particles, a hundred billion and one particles fo normal matter came into being. Then, nearly all of the hundred billion antimatter particles collided with matter particles and anihilated. Everything that currently exists in the universe is that one/one hundred million partice;s that did not have antiparticles with which to anihilate.