Where does energy come from?

  • #26
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You are correct jarekipe in saying that we use it to predict.
 
  • #27
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Does anybody have a theory on what existed before the big bang and what caused the big bang? There must have pre-existed energy to create that kind of a bang!
 
  • #28
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Yes they do. Try mathematician George Spencer Brown's Laws of Form(1969). I'm not sure it would be right to say that he himself agrees with BB theory, but his theory of cosmogenesis is consistent with it. It is fundamentally based on the idea of symmetry-breaking, but is a psychophysical theory rather than a strictly physical one. There are others.
 
  • #29
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Perhaps Before the Big Bang is the wrong way to think about it, because that's like saying North of the North Pole. And there's some very fundamental underlying concepts here such as What Is Time? and What Is Energy? I could give you my views, but they aren't physics, and this is a Physics Forum. So you'll have to wait for somebody who can give you an authoritative answer. Meanwhile you could search Google on "Before the Big Bang".
 
  • #30
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Farsight said:
There's another thread about "Hawking radiation":

https://www.physicsforums.com/showthread.php?t=125554

The idea is that "virtual particle pairs" are created near the event horizon. The negative energy fluctuation falls into the black hole, and the positive energy fluctuation is freed into the Universe. So in this respect black holes would be creating energy.

I have to say I'm not utterly convinced by this myself.
from what i understand of this the black hole is not creating energy it is substituting some of it's mass for energy. just like a nuclear reaction does.
 
  • #31
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Good point.

Edit: I wish I'd thought of that.
 
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  • #32
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Irresistible_Force said:
Ok, from the big bang, to the Stars, as radiation to the plants, eaten by animals that I just had for supper...no really.

So really, where does it come from?
From the big bang. The energy of the universe is the sum of the kinetic energy of each particle, and the potential energy interactions. Mass is equivalent to energy via E = mc^2, so throw that in too. There is the same amount now as there was 1 sec following the big bang. Why/How all this energy was created is not known. It should be noted that net energy is what's conserved, so a particle and it's antiparticle both created out of nothing doesn't violate any conservation laws. That's the basis of Hawking radiation (black holes radiating energy). My personal theory, which is not backed up by observations at all, as that there is another universe which consists of what we'd call anti-particles. The fact that there is much more matter than anti-matter in the observable universe hasn't been explained.

Energy/mass which falls into a black hole isn't lost. It's in the black hole, and will eventually be radiated out. There are entropy issues involved in black holes (information loss) which haven't been resolved, but not energy.

There's a book out now called "The Final Theory" by Mark McCutcheon. Don't read it, except to test your physics muscle in pointing out his errors. Terrible book, everything in it is wrong. He brought up a similar point to the magnetic field argument, involving gravity: How can the moon be held in orbit indefinitely, having a seemingly inexhaustible gravitational force act upon it, meaning the Earth has infinite energy?

The answer, which is always the case for orbits, is that the force is perpendicular to the change in velocity. The speed of the moon doesn't change in its orbit, hence its kinetic energy stays the same. It's (roughly) the same distance from Earth, so V = -GM/r is constant. The velocity of the moon is changing though, since velocity is a vector quantity, even though its magnitude stays constant its direction changes. Because of this acceleration the moon radiates energy away. In this case, the energy radiated is extremely small, and is almost unnoticeable. Qualitatively, the same thing would happen in an atom, if QM weren't true.
 
  • #33
This is a question I find fascinating and have no answer. I have read the answers but I believe there is more to a magnet than meets the eye. I believe there is another force at work that we have not discovered. I am not referring to magnetism itself as I belief a magnet may simply act as a lens for another energy source that we know little about such as gravity. Notice the mathematical formulas for gravity and magnetism are similar. Some of the answers refer to work and state that a magnet does not perform work therefore does not expend or require energy; I say it does work when it is stuck to another object as it defies gravity without any external energy source. In fact magnets can support holding weights many times their own mass. I have no answer for this but who ever unlocks this mystery will be worth a fortune.
 
  • #34
diazona
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This is a question I find fascinating and have no answer. I have read the answers but I believe there is more to a magnet than meets the eye. I believe there is another force at work that we have not discovered. I am not referring to magnetism itself as I belief a magnet may simply act as a lens for another energy source that we know little about such as gravity. Notice the mathematical formulas for gravity and magnetism are similar. Some of the answers refer to work and state that a magnet does not perform work therefore does not expend or require energy; I say it does work when it is stuck to another object as it defies gravity without any external energy source. In fact magnets can support holding weights many times their own mass. I have no answer for this but who ever unlocks this mystery will be worth a fortune.
umm... "defying gravity" to you evidently just means not falling down. It doesn't take any energy not to fall down.

There's nothing special about a magnet holding up something many times its own mass. In fact the mass of the magnet itself has nothing to do with how much it can hold; only the strength of the magnet does. The magnet itself is just like a chain link between the thing being held up, and the thing holding the magnet up. Surely you can imagine a very lightweight yet very strong link in a chain...

And there's really no mystery about magnetism. If you want to think it's mysterious, then I suppose that's your right, but physics has a perfectly good explanation for why magnets work the way they do. (Of course, there is the open question of "unifying" gravity and everything else - you're not the only one who's noticed the similarity between the equations of gravity and magnetism. But that's just about making the theories look nice; it doesn't change the fact that they work.)
 
  • #35
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This is a question I find fascinating and have no answer. I have read the answers but I believe there is more to a magnet than meets the eye. I believe there is another force at work that we have not discovered. I am not referring to magnetism itself as I belief a magnet may simply act as a lens for another energy source that we know little about such as gravity.
Many of the fundamental forces that initially seem separate have been shown to be manifestations of the same force. For example, the electric force and the magnetic force have been discovered to be caused by the same thing. That's why we now refer to it as one force, the electromagnetic force. If I recall correctly, you can actually derive the magnetic force from the electric force + special relativity...but I could be wrong about that. Since then they discovered that the weak nuclear force is also caused by the same thing as the electromagnetic force, so all three together are called the electroweak force. It seems that the strong force and gravity are not part of the same force. However, according to the standard model all forces are mediated by gauge bosons which is why their formulas may look similar. The difference is that they use different kinds of bosons.

Some of the answers refer to work and state that a magnet does not perform work therefore does not expend or require energy; I say it does work when it is stuck to another object as it defies gravity without any external energy source.
Actually permanent magnets can do work and then do have stored energy. A permanent magnet can be demagnetized from the magnetic load put on it. Have a look at the demagnetization curve: http://femm.foster-miller.net/wiki/PMEnergy
 
  • #36
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Notice the mathematical formulas for gravity and magnetism are similar.
What formulas?
 
  • #37
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According to our current knowledge of physics, energy can never be created or destroyed, merely changed in form. So mass can be converted to energy, if you move an object in a positive direction in a gravitational field will transfer energy from yourself to the energy, where it is stored as gravitational potential energy. If the object is then allowed to fall, this will be converted by the gravitational field into kinetic energy, etc etc.

Moving a charged object or magnetic object in an electromagnetic field is the same principle. You need to use your own energy to move the object in the field and this has a corresponding effect of inducing a current (which will be in the opposite direction to your movement in order to resist said movement). Your energy will come from chemical reactions from plants and animal products that you have ingested, these will have gotten energy from the fusion reaction of the sun and the sun got it's energy from hydrogen atoms, and so on back to the big bang.

As for destroying energy... this definitely doesn't happen, but it can be 'effectively' destroyed through heat loss, as this is a loss of energy into heat dissipation that is essentially unusable by anything. This is, AFAIK, the way entropy increases in thermodynamics.

And a black hole can evaporate from hawking radiation. I think our current standard theories on the matter reckon it would take longer for a black hole to evaporate like this than there is predicted time left in the universe. Otherwise a black hole could conceivably become an entropy reducing mechanism in the universe, with energy being 'wiped clean' by the process of being sucked into the black hole and released again as hawking radiation. This is acceptable on a local scale (entropy and thermodynamics is after all statistical. Local fluctuations in the opposite direction to entropy are possible) but not on a massive scale such as an entire black hole disappearing into negative entropy.
 
  • #38
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Actually permanent magnets can do work and then do have stored energy.
There is no stored energy in a permanent magnet. Poorer quality magnetic materials become demagnetized with use because the magnetic domains don't hold the magnetized positions under stress as well as the newer magnetic materials do. Given the same initial magnetization, old fashioned hardened steel will lose it's magnetism relatively quickly with use, but the average ferro-ceramic magnet, as in an audio speaker, a newer, better material, will stay magnetized indefinitely despite constant use. In the case of the former no energy is being expended by the magnet with each use, rather, the orientation of the magnetic fields of its "domains" are all going out of alignment. In the latter, better, material the orientation is not subject to slippage like this.

Again: a magnet is not using up some fraction of the energy used to magnetize it when it interacts with something else. The process of magnetization is simply to align the magnetic fields of the tiny "domains". How fast they go out of alignment has nothing to do with the strength of the magnetic field that aligned them, it has to do with the material used.

We can use a magnetic field to store energy, but only in the sense we can use a spring to store energy. A magnetic field is not an energy source any more than a spring is an energy source.

If I tie a string to a magnet and hang it from a tree then stick a piece of steel to the magnet the magnet is doing no more work holding the steel up than the tree is doing holding the magnet up. The force in play here ("working against gravity") is just the resistance of molecules and molecular bonds to deformation. As diazona said, the magnet is no different than a piece of chain link here.
 
  • #39
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To express things really crudely we can say that if it moves or if it can make things move it is energy.Matter is the stuff and energy the thing that can move the stuff.We can define energy and we can discover conservation laws and come up with theories and all the rest of it but these things are just summaries and descriptions of what we are able to observe.Observations,which are severely limited, are key to what is done in physics and with a small amount of confidence we might be able to state ,for example that mass/energy is conserved justifying this on the basis that with the limited observations made so far this always seems to be the case.
Why is it conserved and where does mass/energy come from are really big questions but I am fairly confident with my answer;
I haven't got a clue.

:uhh:
 
  • #40
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nuclear explosions ,
 

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