TRUTH - What is it? ...The Quantum Vacuum Flux?

[PolyHedral]

Thx PolyMan - nice "avatar",

Thank you.

I don't understand the underlined portion above - it should be positive grav. PE - by definition. I guess I'm not following your logic, if you can bear with me a bit here. If I am pushing the mass so that it travels at a constant speed, there is no KE imposed upon it. And when that object accelerates toward the earth it's gaining KE from an apparent source - its grav. PE.

If you are pushing the mass through a gravitational field at a constant speed, you will be adding kinetic energy to it. After all, if you pushed it once, and then let it move, it would slow down.

Two masses have zero PE if they are infinitely far apart based on Newton's universal gravitational law (F = product of masses divided by the square of distance separating them times the universal gravitational constant - 6.673 * 10 -11 Nm2/kg2) They have a positive grav. PE otherwise. Where does the zero grav. PE come into play here? It has to have something to do with the black hole.

The equation you have just quoted describes the gravitational force. This will tell you how the masses will accelerate. What you're looking for is gravitational potential, which isn't the same thing. To get potential from force, calculus can be used. (Specifically, integrating GMmr^-2dr.) The result is that the gravitational potential is actually -GMm/r. As you can see, that equation includes a negative sign, hence negative gravitational potential.

I don't agree with the bold text above. Two pieces of matter which are close to each other have greater grav. PE (not less) than the same masses farther apart - based on Newton's universal gravitational law. :thud:

But remember that they gain energy when they fall together. Two pieces of matter closer together will collide sooner then if they were further apart, and so can "fall" for less time, and so gain less energy. That is why potential energy increases with distance.

The energy he's talking about cannot be gravitational PE. Also, the third law of thermodynamics says that the total energy of the universe is constant, and not zero. (The third law of thermodynamics states that the entropy of a system at absolute zero is a well-defined constant [and not "0"]. Hence "it is impossible by any procedure, no matter how idealized, to reduce any system to the absolute zero of temperature in a finite number of operations.") So how can the total energy be zero, if we are not, and can never be, at absolute zero? ...based upon Newton and thermodynamics.

The third law of thermodynamics tells us that the energy content of a closed system is constant, and that the temperature is not zero. This is not quite the same as "Energy is not 0," since there are some mechanics that generate negative energy.

This has to be based on some quirk of black holes... classical and even relativity physics don't allow for the total energy of the universe to be "0".

There are many solutions in Relativity that allow for zero total energy, even with non-flat spacetime and non-empty universes.

Hawking seems to be suggesting the 'zero energy' concept perhaps because it is attractive since it avoids the obvious problem of a universe that sprang from nothing to something. The only way our universe does not require a God to have come into existence is if the total energy is and always has been "0". But it still has issues since we cannot then reconcile where the impetus to initiate the BB came from. Even with a total zero energy, we still need an uncaused cause.

In quantum mechanics, uncaused causes are commonplace.

If we have a zero-energy universe, then all one needs is just a tiny bit of energy to get the whole thing started (that is, a tiny volume of energy in which inflation can begin). The universe then experiences inflationary expansion, but without creating net energy. But we still must ask, "What produced the energy before inflation at the initial period of the BB?" That is the real question. All these ideas still require an uncaused cause - cannot get away from that - we keep pushing it back farther and farther into "time" - but it is still there, staring back at us.

Actually, the Big Bang does not require an uncaused cause at all. It does this by saying that there is a first moment of time, at which point the universe already existed. Talking about what came before the first moment in time is nonsensical.

 

[BadDog]

Thank you.


If you are pushing the mass through a gravitational field at a constant speed, you will be adding kinetic energy to it. After all, if you pushed it once, and then let it move, it would slow down.

BD: Actually, as I said if you are pushing it at a constant speed, there is no change in KE.


The equation you have just quoted describes the gravitational force. This will tell you how the masses will accelerate. What you're looking for is gravitational potential, which isn't the same thing. To get potential from force, calculus can be used. (Specifically, integrating GMmr^-2dr.) The result is that the gravitational potential is actually -GMm/r. As you can see, that equation includes a negative sign, hence negative gravitational potential.

BD: Of course -you're right. The PE (grav.) = mgh - directly proportional to the distance of separation. So the PE = 0 when touching and increases as you get further apart. Correspondlingly, the work needed to separate them = Fd.


But remember that they gain energy when they fall together. Two pieces of matter closer together will collide sooner then if they were further apart, and so can "fall" for less time, and so gain less energy. That is why potential energy increases with distance.

BD: Actually, the energy changes form. Energy cannot be created/destroyed. Agreed about PE increasing w/ distance.


The third law of thermodynamics tells us that the energy content of a closed system is constant, and that the temperature is not zero. This is not quite the same as "Energy is not 0," since there are some mechanics that generate negative energy.

BD: It says that we cannot reach absolute zero (0 K). Name a mechanic that generates "negative energy." I'm not disputing you, but the issue is that the total E does not change. And the third law of thermodynamics states that "the entropy of a system at absolute zero is a well-defined constant." [and not "0"] Entropy is energy related to disorder of disorder.

There are many solutions in Relativity that allow for zero total energy, even with non-flat spacetime and non-empty universes.

BD: Can you give an example? Thx.


In quantum mechanics, uncaused causes are commonplace.

BD: ?? Example?


Actually, the Big Bang does not require an uncaused cause at all. It does this by saying that there is a first moment of time, at which point the universe already existed. Talking about what came before the first moment in time is nonsensical.

Comments in green above.

Thx,

Gotta go. I'll address the last comment when I have time. (Class now.)

BD

 

[BadDog]

Well, I'll be going out of town during our Spring break, and don't know if I'll be back here soon. take care,

BD