Answerer

Okay guys, most of you are claiming that the gravitiational force(or spacetime curvature), like the other forces, has a theoretically infinite range and is extremely small at large distance. But note that I'm not talking about theoretical cases, I'm talking about practical cases. The actual limit of our gravitational force, on whether is it bounded within our universe or does the force extend beyond our universe? And yes, I am talking the 'absolute' upper range of the gravitational force.

SanDiegoAtheist

The answer to that is that we simply don't know.

We MIGHT know someday, but given that we are limited to our universe, and it's unlikely that we'll be able to ever leave it, we can't make any observations about what is 'outside' of our visible universe.

If we can ever put together a Grand Unified Field Theory, we might have an answer, but even then, that theory would have to be able to make absolute deductions about what is outside of our universe to be able to answer your question - and we don't know if that is or will be possible.

Even if we do ever have a unified field theory, and it does make absolute predictions about the outside of the 'universe', if we can't make observations 'outside' our universe, we will never be able to check those predictions - thus, the unified field theory may be correct as far as we can check it in THIS universe, but might be completely wrong as applies outside (much as Newtonian mechanics seemed absolute until this century, since we didn't have the tools or ability to make the observations that would falsify it until recently).

Cheers,

The San Diego Atheist

DNAunion

DNAunion: The upper ranges on the forces are due to the different lifespans of their associated force-carrying particles, which are exchanged between things that respond to that force.

The maximum lifespan of an exchange particle is determined by its rest mass in conjuction with the Heisenberg uncertainty equation. In short, the more massive the exchange particle, the shorter is its maxium lifespan.

Gravity is theorectically mediated by massless gravitons. Being massless, they can exist indefinitely, just as photons can.

On the other hand, the weak force is mediated by W and Z bosons, and the strong force by gluons. Since these particles DO have rest masses - and indeed quite large rest masses - their maximum lifespans are extremely short.

The lifespan determines the maxium range of the force because c limits the speed at which things can exchange particles, so the less time available before the particles "blink out of existence" the closer the things exchanging them have to be.

So, the greater the mass of the exchange particle, the shorter the maximum lifespan. The shorter the maximum lifespan, the shorter is the distance that it can travel before "blinking out of existence" (keep in mind that "Stuff" has to exchange these particles in order to feel the force they mediate).

tronvillain

Do those particles actually have absolute maximum lifespans, or do they have half-lives which impose a practical maxmum lifespan?

DNAunion

DNAunion: They are absoluate maximum lifespans, not probabilitistic ones in which half of the population outlives the halflife.

Exchage particles cannot "exist" for any longer than calculations show or they would be in violation of the Heisenberg uncertainty inequality: the energy "borrowed" to create the exchange particles must be paid back within a span of time dictated by their mass, with the greater the "debt" the shorter the life of the "loan".

Answerer

Just curious DNA, while I know that the gravitons must obey the uncertainity principles, is there a minimum amount of energy that gravitons could carry?

DNAunion

DNAunion: Just to make sure...physics really isn't my forte. I've made several errors here at Infidels and elsewhere when it comes to modern physics, so it wouldn't hurt for people to confirm what I say before repeating it.

Since photons (and even electrons and protons) have a wave frequency, I imagine that gravitons do too, and that it would be quantized according to Planck's E = hf.

DNAunion

DNAunion: What is the range of the weak force? I figured it out by hand a few weeks ago when I needed it for a discussion. The following shows the principles involved in determining the range of a force.

The only input needed is the mass of the particle. For the W bosons that mediate the weak force it is 80.4 Gev/c^2 (found it in a book).

*************

First we need to figure out how long a virtual W can exist. The Heisenberg equation of interest is:

[delta]t = h / (4[pi]E)

Looking up the value of h we find h = 6.63 x 10^-34 Js, so substituting we get:

[delta]t = (6.63 x 10^-34 Js) / (4[pi]E)

pi is approximately 3.14 so 4 times that is about 12.6 (keeping it to three sig figs). Substituting that we get:

[delta]t = (6.63 x 10^-34 Js) / (12.6E)

******************

Second, we need to calculate the energy of a W boson, in Joules. We use Einstein's energy-mass equivalence equation:

E = mc^2

The mass of a W is 80.4 Gev/c^2, so substituting we get:

E = (80.4Gev/c^2)c^2

The c^2's cancel out, leaving:

E = 80.4Gev

The conversion factor we need is 1Gev = 1.60 x 10^-10 J. Substituting we get:

E = 80.4(1.60 x 10^-10 J) = 1.29 x 10^-8 J

************************

Third, we substitute the value for E from step 2 into the final equation from step 1.

[delta]t = (6.63 x 10^-34 Js) / [12.6(1.29 x 10^-8 J)]

The joules on top and bottom cancel out, (and the two decimal values in the denominator can be multiplied together) leaving:

[delta]t = (6.63 x 10^-34 s) / (16.3 x 10^-8 )

Doing the division we end up with:

[delta]t = 4.07 x 10^-27s

Thus, a virtual W boson can exist for no longer than 4.07 x 10^-27 seconds.

***************************

Next, we figure out how far a virtual W boson can travel before it "disappears". We use c for the speed since that is the maxium speed a particle with rest mass can achieve.

Here's the simple distance formula:

d = vt

We know the velocity, v, is the speed of light in a vacuum, or c.

d = ct

d = (3.00 x 10^8 m/s)t

And we know t from out first set of calculations.

d = (3.00 x 10^8 m/s)(4.07 x 10^-27s)

The second cancel out, leaving:

d = (3.00 x 10^8 m)(4.07 x 10^-27)

Doing the multiplication gives us:

d = 1.22 x 10^-18 m

Thus, the maxium distance a virtual W boson can travel before "disappearing" is 1.22 x 10^-18 m (or 1.22 x 10^-16 cm).

Therefore, the maxium range of the weak force is 1.22 x 10^-18 m. Just to get an idea, compare that to the diameter of a proton and you will find that it is much less.

As you can see, once you plug a particle's mass in, the rest follows: the lifespan and maximum distance are functions of mass.


PS: I later found a confirmation for my calcuation:

Answerer

Yeah, your nick seem too biologically to me.

Wiploc

Gravity propagates at the speed of light. Therefore, it has not propagated beyond the "edge" of our universe yet. As it propagates beyond where the edge is now, that moves the edge. If we have an edge. This is about where I go incoherent.

crc