Gravity?

[Juggernaut]

Re: Not soooo wrong.

Originally posted by Sagacious Dolphin
A greater rate in change of potential (with respect to distance) would.

*cough* Yes, that's what I meant.

[KrazyHorse]

Originally posted by Lancer
What is a 'graviton'?

A figment of the imagination of those who wrongly believe that gravity is a force like any other.

[KrazyHorse]

Originally posted by our_man
Gravity...

I've always wondered - does Archimedes Principle still hold true in space? If so, couldn't the bouyant force it generates offset the effects which the absence of gravity causes in astronauts?

Which Archimedes principle? A floating object displacing its own mas obviously has no meaning, as there is no such thing as floating on the non-existent surface of the liquid. A submerged mass will still displace its own volume, however.

[KrazyHorse]

Note: there is no buoyant force in an inertial frame, as it is caused by a downward pull on the liquid medium.

[TCO]

Just read an old sci fi story about some rocket pilots that had to make a aseveral day run at 3 G's and were wasted by it. Anybody know what the effects of long time exposure to serveral G's is?

[KrazyHorse]

Nope. I doubt they've ever done that to a person. They killed enough people running them up to 20g's and holding them there for 15 seconds. I think there were limits, even for the USAF of the 50s.

[Urban Ranger]

What about magnetic monopoles?

[TCO]

Originally posted by KrazyHorse
Nope. I doubt they've ever done that to a person. They killed enough people running them up to 20g's and holding them there for 15 seconds. I think there were limits, even for the USAF of the 50s.

Yeah, I've heard about the high G work for short periods of time. (for fighter pilots doing a dive pullout.)

Interesting thing about this story, written in 1953 was that it seemed to know about all the pullout research. But the situation poisited was a high speed run (to deliver medicine to Pluto!) at 3.5 G's. (takes about 16 days.) 3 G's for a few minutes is no big deal. Just wonder what the effect would be for days.

[Lancer]

"A figment of the imagination of those who wrongly believe that gravity is a force like any other"

KH, that's interesting. Though I'm sure you can make such a statement based on science, I had the same inclination as a gut feeling. How can a bit of something go out to another bit of matter and pull on it? First it has to go outward, and then when it gets there it has to pull towards itself.

Lots of things push, yes? Light, sound waves, wind... When wind hits you it continues in the same direction as it went in when
it travels towards you. It doesn't blow to you and then, when it gets to you, push you in the direction it came from. That's what gravity does. It seems to obey a different set of laws entirely. I call these laws, the 'WTF' laws.

Also, consider a wind that blows in all directions from every bit of matter in existance...man, it makes my brain hurt.

[Adalbertus]

Just read an old sci fi story about some rocket pilots that had to make a aseveral day run at 3 G's and were wasted by it. Anybody know what the effects of long time exposure to serveral G's is?

About the feeling a woman might have after several consecutive days ****ing with someone of twice her weight

A floating object displacing its own mas obviously has no meaning, as there is no such thing as floating on the non-existent surface of the liquid

partly wrong. Floating requires gravity, sure. But there can be liquids without gravity. If you don't do anything to it the liquid will assume the shape of a sphere, due to the surface tension. Depending of the interactions between the liquid and the object you want to "float" the object will be either dragged into the liquid or be repelled. The same effect as wetting.

[Adalbertus]

Lots of things push, yes? Light, sound waves, wind... When wind

The fundamental forces (gravity, electromagnetism, weak and strong interaction) don't work like a wind. It's, for the last three, an exchange of "virtual" particles which are constantly emitted and absorbed by a charged body. "Virtual", because they locally violate conservation of energy, but the time these particles "exist" is so short that the violation is permitted by the uncertainty relation. Unlike a wind, this can also result in an attraction.
I'm not working in this areas, so I cannot give an explanation on how everything "really" works, even if an explanation exists in a form other than three books of maths.
The best working theory for gravity, General Relativity, explains the gravitational attraction by a curvature of spacetime. So the moon moves along a straight line but the straight line is curved in spacetime (which is one problem many people have with Relativity: It requires a geometry different from what we are used to, with our three space dimensions and one time dimension which are entirely separated. Relativity mixes this up a bit).

What about magnetic monopoles?

Some physicists firmly believe in them, some don't. I don't. We'll have to see.

[Rogan Josh]

KH: Why don't you like the graviton? It seems a nice, perfectly natural extension of the ideas which Adalbertus has already explained (about virtual force carriers) to gravity.

Let me add one point. All of these force carrying particles come about from the requirement that symmetries be local. For example, it was observed that quantum mechanics has a U(1) symmetry: basically, physical observables only depend on the modulus squared of the wavefunction, so you can multiply all the wavefunctions everywhere by a constant phase exp(i*phi) and get exactly the same results. However, since special relativity tells us that we cannot send information faster than the speed of light, we cannot change the wavefunction everywhere at the same time (indeed, what does 'the same time' even mean?). Logically then, the symmetry should be 'local': we should be able to change the phase of the wavefunction locally (at a point) without affecting the results. When you look through the equations, you find that in order to do this you need to have an extra particle, which, in this case is the photon.

Similarly, the insistence of SU(2) symmetry and SU(3) symmetry leads to the requirement of the W and Z bosons and the gluin respectively, all now seen in experiment. Amazing!!!

Now, one of the exciting things in particle physics these days is the search for Supersymmetry: that there is an extra fundamental symmetry of the universe, between bosons and fermions (particles with different spins). Global supersymmtry answers a lot of problems we have with the current models and is present in all string theories. However, the really exciting thing, to my mind, is that in order to make supersymmetry local, we need a new particle (just like before) which is the graviton. We can explain gravity as local supersymmerty!!! Even more amazing!!!

The really intreguing question is: why is gravity so weak?

[Dauphin]

I don't like gravitons because of the equivalence principle.

If gravitons are emitted by mass-energy bearing particles then you can tell the difference between a non-inertial frame of reference and gravitional attraction.

[Dauphin]

Rhetorical questions

we need a new particle (just like before) which is the graviton

If the photon is propogated by Electric and Magnetic fields, the graviton will be propogated by .......???

Gravity is akin to the electric charge (sort of), so is there as yet unmeasured gravity equivalent to the magnetic field? Would a moving mass current generate an ever so weak magneto-gravitional field which repels other mass-currents?

[Solly]

It seems that physicists don't have a clue what makes gravity and make up rules and theories...

How can a force be exerted on me without any other properties at all...