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Energy
- Thread starter Tangata
- Start date
michabo
reason, evidence
The same amount of energy has existed forever. The most common formulation of the Big Bang theory actually describes the universe as having no net energy. The energy tied up in matter is balanced by the negative energy of gravitational fields. You can read up on this in Alan Guth's "The Inflationary Universe".
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J
Jet Black
Guest
as the equation really implies, it has existed since the beginning of time (since without time the equations are meaningless), and is conserved in all classical and quantum interactions. Note that this does not take curved space, or string theory into account.
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Very well put, but I believe Gravitation is a negative force, not negative energy. (I may be wrong, I'm not exactly educated in Quantum Physics as I am in the more familiar sciences.)michabo said:
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Fascinatingmichabo said:
The next time I visit the library, I'll take a look at "The Inflationary Universe".
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Deamiter
I just follow Christ.
I have not read this book, but my understanding on the subject of negative energy is that it is purely hypothetical. Granted, a universe with 0 net energy has some theoretical perks, but from what I've read, I assumed that as gravity is entirely unexplained as yet, these ideas are just that: speculation.
If I am wrong, PLEASE correct me, but if I'm not mistaken, I simply think it's important to identify the difference between speculation and real evidence for a given theory. We talk about truths so often that it could be easy for some to miss the fact that this part of the Big Bang theory is purely theoretical. In the future, the results that this hypothesis predicts will be examined, and then we will know for sure.
If I am wrong, PLEASE correct me, but if I'm not mistaken, I simply think it's important to identify the difference between speculation and real evidence for a given theory. We talk about truths so often that it could be easy for some to miss the fact that this part of the Big Bang theory is purely theoretical. In the future, the results that this hypothesis predicts will be examined, and then we will know for sure.
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michabo
reason, evidence
If I understand you correctly, you are asking why we should accept such a crazy idea, one which seems to contradict our ideas of the world. Instead of making up such stuff, shouldn't we just accept that the conservation of energy is broken? To borrow an analogy, we might propose the law of conservation of height in children, saying their height is conserved as Total Height = Current Height + Potential Height. This offers us no useful predictions as there is no way of measuring potential height, so we reject the idea. On the other hand, the conservation of energy makes many useful predictions, and when we incorporate the idea of negative energy, we can calculate all sorts of things: trajectories of artillery shells, the motion of a long jumper, the motion of the planets, and so on. And so, from a positivist viewpoint we say that children's height is not conserved, and energy is. We also say that, even though negative energy isn't immediately intuitive, it also exists.
As it happens, negative gravitational field energy isn't as counterintuitive as it sounds. We're probably all familliar with the idea of gravitational potential energy, right? Whenever we describe the motion of a ball being thrown into the air, we always subtract the potential energy, TE = KE - GPE (Total energy = Kinetic Energy - Gravitational Potential Energy), so we're used to the idea that some forms of energy are additive, while others are subtractive. When we ask "what is the total energy of this ball", we sum up all of the energy of motion, mass, electric charge and then *subtract* the energy tied up in its gravitational field. So really, this isn't such an unusual idea, it's just likely not something we've thought of before.
As it happens, negative gravitational field energy isn't as counterintuitive as it sounds. We're probably all familliar with the idea of gravitational potential energy, right? Whenever we describe the motion of a ball being thrown into the air, we always subtract the potential energy, TE = KE - GPE (Total energy = Kinetic Energy - Gravitational Potential Energy), so we're used to the idea that some forms of energy are additive, while others are subtractive. When we ask "what is the total energy of this ball", we sum up all of the energy of motion, mass, electric charge and then *subtract* the energy tied up in its gravitational field. So really, this isn't such an unusual idea, it's just likely not something we've thought of before.
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Negative energy is not so counterintuitive as you might think - its just the result of where you put your baseline.
(Just gonna restate what michabo said a bit more formally now, sorry if its over-egging the pudding...)
For example, take the surface of the Earth as height = 0. Gravitational potential energy (g.p.e.) is (mass)*(gravitational field)*(height), so a ball weighing 1 kg on the surface of the Earth has zero g.p.e.; however if we define our coordinate system with height = 0 at a level 10 metres above the ground, the ball has 1kg*10Nkg^-1*-10m = -100 joules g.p.e.! So the absolute value of energy is not so interesting as it depends on where we put our zero-point (I'm aware this is a v simple Newtonian model, but the principle still applies). The interesting part is that whatever the value of the total energy of the universe is, it always remains the same
EXCEPT
when we consider the Heisenberg uncertainty principle. This can be recast from the position/momentum principle to a time/energy principle:
delta(energy)*delta(time) ~ hbar
where hbar is Planck's constant divided by (2 * PI). This basically states that a particle, or particle pair, of total rest mass energy delta(energy) may exist for a period delta(time) defined by the above relation (note that this time will be of order 10^-14 seconds = 0.00000000000001 seconds for a very low energy particle). This means that on the quantum scale consevation of energy may be violated! It is all very interesting
In answer to your question, I don't know. If by "forever" you mean since the Big Bang, then yes, energy has always been conserved in a macroscopic sense (as far as we know) i.e. not including the short-lived particles mentioned above. If you mean before that, then I really don't know. My personal belief is that, as conservation of energy may be violated (albeit on very short timescales), energy must be a manifestation of a deeper, more fundamental quantity that is ALWAYS conserved. But that is just what seems logical to me.
(Just gonna restate what michabo said a bit more formally now, sorry if its over-egging the pudding...)
For example, take the surface of the Earth as height = 0. Gravitational potential energy (g.p.e.) is (mass)*(gravitational field)*(height), so a ball weighing 1 kg on the surface of the Earth has zero g.p.e.; however if we define our coordinate system with height = 0 at a level 10 metres above the ground, the ball has 1kg*10Nkg^-1*-10m = -100 joules g.p.e.! So the absolute value of energy is not so interesting as it depends on where we put our zero-point (I'm aware this is a v simple Newtonian model, but the principle still applies). The interesting part is that whatever the value of the total energy of the universe is, it always remains the same
EXCEPT
when we consider the Heisenberg uncertainty principle. This can be recast from the position/momentum principle to a time/energy principle:
delta(energy)*delta(time) ~ hbar
where hbar is Planck's constant divided by (2 * PI). This basically states that a particle, or particle pair, of total rest mass energy delta(energy) may exist for a period delta(time) defined by the above relation (note that this time will be of order 10^-14 seconds = 0.00000000000001 seconds for a very low energy particle). This means that on the quantum scale consevation of energy may be violated! It is all very interesting
Tangata said:
In answer to your question, I don't know. If by "forever" you mean since the Big Bang, then yes, energy has always been conserved in a macroscopic sense (as far as we know) i.e. not including the short-lived particles mentioned above. If you mean before that, then I really don't know. My personal belief is that, as conservation of energy may be violated (albeit on very short timescales), energy must be a manifestation of a deeper, more fundamental quantity that is ALWAYS conserved. But that is just what seems logical to me.
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