# Do all the objects in the universe exert force on all other objects?

Do all the objects in the universe exert force on all other objects? Like a type of gravity; also, how much does it decrease as it gets farther away?

• Curious about your thinking behind the wording "like a type of gravity". Are you seeking a force with infinite reach other than gravity? Sep 24 '13 at 23:51
• The responses given so far have a distinctly "Newtonian" flavour. The appropriate gravitational theory for this question is of course Einstein's and from that we learn that everything within our causal horizon effects us gravitationally. Whether material beyond our causal horizon can have influence is technically far more complex and depends on a number of assumptions about the initial conditions for the cosmic expansion. Anyone care to address that? Jan 13 '15 at 22:48
• Anybody that thinks they can answer this question needs to think back to the days before we knew of the existence of dark energy and dark matter. We detect things (including those mentioned above) by the effect (force) they have on other things. If there was an object in space not exerting any force on another object, we wouldn't know that it is there. Sep 14 '15 at 15:39
• Also, the only known "free" mass-less particle (now that the neutrino is thought to have mass) is the photon which does exert a "force" in the sense that it has momentum p = h/(wavelength). This is what "pushes" solar sails (radiation pressure). Particles with mass, of course, "exert" gravity. Sep 14 '15 at 16:04
• One more thing. We only know of 4 forces. The strong and weak forces fall off with distance so quickly (short lifetime of particles that carry the force) that they are confined to distances around the size of a nucleus. The other two we know well (electromagnetism and gravity). There is no "kind of like gravity" force as far as we know. Sep 14 '15 at 16:21

Yes - this is the formula:

$$F = G\frac{m_1m_2}{d^2}$$

Using this equation, we can say that all atoms in the universe exert force upon eachother. One carbon-12 atom has a mass of $1.660538921(73)\times10^{-27} kg$. That's a crazy small mass.

Now let's say that these two atoms are 100,000,000 light years apart. That's $9.461\times10^{23} m$, which is a very long distance.

Now, if we plug these values into our equation, we get that the force is: $1.709191430132 \times 10^{-59} N$

That's a very, very small amount of force. But it's still force.

No. It's impossible for every object to interact with every other object, due to the assertion by general relativity, that the universe can, and is, expanding faster than the speed of light.

I then assume that the universe initially was expanding at, or close to the speed of light, and that it immediately after the big bang was expanding faster than the speed of light.

Some of the particles/forms of energy that would have reached us are also bound to have been "held back or deflected", even in the young stages of the big bang, and are now at a distance at which they can never reach us. They could have been held back by for example a black hole.

Potentially, if the expansion of the universe at one point was so slow that gravity from every particle had time to propagate to every other particle, then yes - every particle and energy in the universe affects every other particle.

• This is incorrect. The prediction from General Relativity is that the graviton is massless, and therefore travels at the speed of light. Additionally, the universe is not expanding faster than the speed of light within our cosmological horizon. Jan 14 '14 at 19:19
• @astromax But there are objects outside of our cosmological horizon? The diameter of the universe is estimated to be some 93 billion light years. Jan 14 '14 at 23:48
• The graviton is also a hypothetical particle which has yet to be observed, and it will most likely never be observed unless it has mass. Jan 15 '14 at 0:04
• The graviton has not yet been discovered directly, but I don't know why you say it will most likely never be observed unless it has mass. It is believed to be a massless particle, and this is why it travels at the speed of light. However, there is indirect evidence that gravitational radiation (gravitons) do in fact exist, and a nobel prize(nobelprize.org/nobel_prizes/physics/laureates/1993/illpres/…) was awarded for this work. We do not know whether or not there are things outside of our horizon. We can neither see them nor feel their effects since all particles are.. Jan 15 '14 at 0:27
• restricted to traveling at the speed of light. Your original statement remains incorrect. Jan 15 '14 at 0:28