Dark Energy/Zero-Point Energy/Tesla

[Az]

OK, now we're getting into the "damn disturbing" area.

[Provost Harrison]

Originally posted by Bill3000
*Pops back into Apolyton roughly 4 or 5 years after he last posted*

First of all, gravity is really differenty from the other fundamental forces; In General Relativity, it is caused by the curvature of spacetime being warped by the presence of matter. (For instance, the acceleration due to gravity on earth is mostly because of time dialation rather than an actual force.) Thus, it cannot have a real potential energy function. However, it is theorized that like electromagnetism, there can be a form of radiation caused by the flucutation of the spacetime fabric. Still, gravity is the weakest fundamental force, and thus it's very hard to even remotely observe this time of radiation (Actuall, it would be a form of length contration and such rather than radiation like light.)

The idea of the rest energy (Don't confuse this with the energy from the rest mass; I mean the energy when the temperature is at absolute zero) was theorized, rather easily using quantum mechanics. But I'm not getting to the point.

The modern version of the "ether" is ironically, the vacuum itself. Quantum field theory is based on the fact that particles can be created from vacuum flucuations (And it is these particles, called virtual particles because they cannot be observed by definition, that cause the forces) The vacuum energy does exist, but still - the point is that even when you include all of the normal mass of the universe and its energies, it only accounts for 5% of the total mass/enegy of the universe. The vacuum energy is actually very small (Believe it or not, 10^-120 smaller than originally predicted) so it cannot account for dark matter and dark energy.

Jesus Bill, where did you get all that from?! Welcome back BTW...all that is needed is the return of The Brain and then armageddon will have commenced

[Bill3000]

*Waves to PH*

When I gave up hope regarding all forms of politics in the 12th grade, I focused myself into the sceinces. actually I've always been a science person, and planned to do something regarding it, but I never actually read into it until I took my first physics course as a senior. Now I'm an absolute nerd when it comes to physics.

[Provost Harrison]

Welcome to science geekdom Bill

[Ramo]

Well, the ZPE comes from the idea that over short times, there's uncertainty in energy (which is a result of the Hamiltionian operator not commuting in general with an arbitrary observable, rather <[H,A]> = i(hbar)d< A>/dt, if you were curious ), causing particles to pop in and out of existence. So, there's a vacuum energy density due to these particles that permeates space. Because pressure can be thought of as -dE/dV, and because energy actually increases when the volume of a given vacuum increases, the pressure due to the vacuum energy density is negative. Now, Einstein's field equations impose a dependence on pressure as well as mass, so imply that the vacuum energy density, in the absence of mass or positive pressure, would cause an outward acceleration.

ZPE is a form of "dark energy." Another form is called quintessence, which is somehow based on temporal variation some scalar energy field, and something I know nothing about.

Dark matter is the stuff theorized to account for what's seen as missing mass.

I've never heard of a Telsa energy.

[Kuciwalker]

Originally posted by Dauphin

Then we have the general observation that contrary to what was generally theorized, at the temperature of 0 Kelvin, atoms do not come to rest

That's a general theory?

I've never heard that theorised in quantum theory, which predicts that nothing is ever at rest.

It predicts that a particle with no definite position is at rest

[Dis]

holy cow, talk about long lost posters.

[KrazyHorse]

Originally posted by DanS
Thanks for your contribution.

With the dolphin, he was the first person to post something with some basis in fact in this thread.

[Lorizael]

Wait wait wait. Did stargate use a real term?

[KrazyHorse]

Originally posted by Ramo
Well, the ZPE comes from the idea that over short times, there's uncertainty in energy (which is a result of the Hamiltionian operator not commuting in general with an arbitrary observable, rather <[H,A]> = i(hbar)d< A>/dt, if you were curious ), causing particles to pop in and out of existence.

It's hard to describe vacuum energy as being due to the uncertainty principle. You need quantum field theory to describe it. Anything else is facile, and should give you an expection value of 0 for the vacuum energy.

[Ramo]

Fair enough. My field theory class ended up being particle taxonomy.

[KrazyHorse]

Originally posted by Bill3000



Who, me? I'm just a freshman undergrad, BME major. Physics just happens to be my passion.

I'm pretty sure he wasn't talking about you. Sorry, dude.

I can think of: 1 physics PhD
2 physics grad students
4 people with an undergraduate degree or most of one in physics...

[KrazyHorse]

Originally posted by Ramo
Fair enough. My field theory class ended up being particle taxonomy.

Same think happened to the undergrad particle course I took.

Part of the reason I decided on CM...

That and he fact that HE theoists have no ****ing clue what they're doing.

[DanS]

Dark matter is the stuff theorized to account for what's seen as missing mass.

Was I incorrect in implying that energy has mass? If so, insert "which composes some 75% of the universe's contents" instead of "which composes some 75% of the universe's mass."

[Bill3000]

Gravity is more accurately described in General relativity by energy rather than mass; e.g. the gravitational effects that we observe on Earth are approximately caused by the Earth's rest energy. (E_0 = mc^2 as the famous equation states) However, energy doesn't have to have mass. The quantum of light, the photon, has energy and momentum, but no mass; (E = m^2c^4 + p^2c^2; reduces to E = pc for the photon) by no mass I mean it has no inertia, travels at the speed of light, etc. Energy is a quantity of measurement, not a "thing" in the sense that it must have matter. Speaking of which, light is effected by gravity.