What is energy exactly?

[questionposter]

I don't know what energy is exactly. I mean I can get how it would just be like this mathematical tool or result, but I just don't see that. Saying that seems like saying time doesn't exist, which exists, just not in the same spacial dimensions we can perceive. And then to confuse things even more, scientists, even though its not technically science even with all the mathematics, predict the existence of strings, which are suppose to be vibrating strands of energy, which means energy its a physical tangible thing in the same sense as a rock. I don't really know how to think of it. AND THEN, there's even photons, which are somehow pure "EM force", which I've heard described as pure energy AND pure momentum AND pure EM radiation.

Edited August 11, 2011 by questionposter

[J.C.MacSwell]

I don't know what energy is exactly. I mean I can get how it would just be like this mathematical tool or result, but I just don't see that. Saying that seems like saying time doesn't exist, which exists, just not in the same spacial dimensions we can perceive. And then to confuse things even more, scientists, even though its not technically science even with all the mathematics, predict the existence of strings, which are suppose to be vibrating strands of energy, which means energy its a physical tangible thing in the same sense as a rock. I don't really know how to think of it. AND THEN, there's even photons, which are somehow pure "EM force", which I've heard described as pure energy AND pure momentum AND pure EM radiation.

 

Welcome to the Club. We are over 6 billion strong and growing everyday.

 

However if you stick to one local (very local in a relative sense) inertial frame we have a pretty good idea, and some pretty good insights beyond that.

 

For the photons, that sounds about right, depending on what you might mean by "pure" in each case.

Edited August 11, 2011 by J.C.MacSwell

[questionposter]

Welcome to the Club. We are over 6 billion strong and growing everyday.

 

However if you stick to one local (very local in a relative sense) inertial frame we have a pretty good idea, and some pretty good insights beyond that.

 

For the photons, that sounds about right, depending on what you might mean by "pure" in each case.

 

Well can you say or can some expert agree that it is in fact a physical thing? And if so, how in what senses? Like what are the best educated guesses?

[DrRocket]

Well can you say or can some expert agree that it is in fact a physical thing? And if so, how in what senses? Like what are the best educated guesses?

 

The best available definition, which is none too satisfactory, is that energy is the conserved quantity associated with the time translation symmetry (Google Neother's theorem). Unfortunately this is all but useless in general relativity.

 

J.C. McSwell is right.

[questionposter]

The best available definition, which is none too satisfactory, is that energy is the conserved quantity associated with the time translation symmetry (Google Neother's theorem). Unfortunately this is all but useless in general relativity.

 

J.C. McSwell is right.

 

So as far as we know, is energy only a purely mathematical consequence of our math, or is it a real thing that exists in reality? Or at the very least, is it a real phenomena?

[DrRocket]

So as far as we know, is energy only a purely mathematical consequence of our math, or is it a real thing that exists in reality? Or at the very least, is it a real phenomena?

 

Pick up a brick. It gains potential energy.

 

Drop it. The potential energy is converted to kinetic energy.

 

Let it land on your foot, where the kinetic energy is absorbed.

 

Is that real or imagined pain ?

[questionposter]

Pick up a brick. It gains potential energy.

 

Drop it. The potential energy is converted to kinetic energy.

 

Let it land on your foot, where the kinetic energy is absorbed.

 

Is that real or imagined pain ?

 

Well that's not what I was getting at exactly. The spin of an electron is purely mathematical because an electron isn't actually spinning, its just a mathematical tool to help find its wave function, like the number 2. The number 2 is just a symbol to help us calculate patterns, its not an existent thing. There can be a value of 2, but 2 itself is just a concept. Is that what energy is as far as we know?

 

 

 

[ajb]

The spin of an electron is purely mathematical because an electron isn't actually spinning,

 

But we can observe physical phenomena that rely on the notion of spin. We can measure spin doing this in reverse. So spin is real.

 

DrRocket's point is that one can also observe phenomena that relies on energy, like dropping a brick on your foot.

 

DrRocket gives the best definition of energy as the property of a system that does not change with time. (Loosely).

[swansont]

Like many quantities in physics, it's a concept that is a convenient bookkeeping quantity. As DrRocket already said, it's conserved because of time-translation symmetry, which makes it useful for the models we construct. There are situations where we can predict what will happen, or not happen, because we know energy is conserved. It represents something real — there are consequences — but physics doesn't pretend that energy is any physical thing.

 

!

Moderator Note

Farsight's response split off; he should know better

http://www.scienceforums.net/topic/59122-energy/page__pid__621381#entry621381

[ajb]

— but physics doesn't pretend that energy is any physical thing.

 

What swansont says is important, energy is a property of a system rather than a physical entity itself.

[mississippichem]

Physicists: I've always casually thought of energy as the thing that makes stuff go (be it vibration, translation, orbital excitation...). Is this compatible with our current understanding? Enlighten an ignorant chemist please.

 

I'm thinking zero point energy might not be compatible with my "street-definition" of energy.

Edited August 11, 2011 by mississippichem

[ajb]

The ideas are compatible.

 

A nice exercise in Newtonian mechanics is to show that the energy defined as

 

[math]E = \frac{m}{2} \left( \frac{dx}{dt} \right)^{2} + V(x)[/math]

 

is constant in time,

 

[math]\frac{dE}{dt}=0[/math] ("on-shell" anyway, that is when the equations of motion hold).

 

But this does not directly show that energy is the "conserved charge" associated with time translations. To do that you need to know a little about the Lagrangian and Hamiltonian formulations of mechanics.

[Greek_Geek]

So as far as we know, is energy only a purely mathematical consequence of our math, or is it a real thing that exists in reality? Or at the very least, is it a real phenomena?

 

I think part of the problem in trying to conceptualize energy is by explaining it as something "physical". That gets dicey when you delve into quantum mechanics where the concept of "physical" starts to lose meaning. Energy is definitely real. Just because you can't conceptualize doesn't mean it doesn't exist. To this day I still have some difficulty understanding gravity. Warping space-time? Well how? Warping with respect to what? How can you warp something when space is the largest frame of reference. Doesn't mean I don't believe it. At some point we have to believe empirical data.

 

I do however know exactly how you feel because I was thinking exactly the same thing once. Best way to put it, energy is the "stuff" that makes everything go into motion, whether it opposes a force, or is induced by a force, or is transferred into a moving object, etc. It is much more than that, but that is a simplistic way to look at it.

[michel123456]

There are a lot of concepts in physics that are like energy: do they "exist" or not?

 

For example: distance.

Do "meters" or "kilometers" exist when you measure a distance? Or what is existing is only 2 objects and some measurement of "space" between them? Then, do "space" truly "exist" by meaning there is "something" between the 2 objects (an aether?)

Another example: time.

Do "seconds" or "hours" exist?

Are they tangible, or are they only a measurement?

 

IOW, do measurements like distance & time, (or energy) truly "exist"?

[ajb]

Best way to put it, energy is the "stuff" that makes everything go into motion...

 

I would agree with this. The standard definition of energy from mechanics is "the capacity to do work". That is energy is the "thing" related to movement and change.

[Mike Smith Cosmos]

Energy Makes things happen !

 

Quite where this - making happen stuff - comes from is an interesting question .

 

 

 

 

N.B

 

 

What does " You must enter a post. " mean ?

Edited September 17, 2011 by Mike Smith Cosmos

[Mystery111]

Energy in Einstein's Relativity is simple a diffused state of matter. That is to say, Einstein's Relativity makes energy and matter as different fascets of the same thing. So energy is a fluctuation and it is a diffused state of matter.

[swansont]

Energy in Einstein's Relativity is simple a diffused state of matter. That is to say, Einstein's Relativity makes energy and matter as different fascets of the same thing. So energy is a fluctuation and it is a diffused state of matter.

 

The m in E=mc^2 refers to mass, not matter.

[Greek_Geek]

The m in E=mc^2 refers to mass, not matter.

 

What is the difference? Matter has mass.

[swansont]

What is the difference? Matter has mass.

 

Mass is a property of matter. They are not interchangeable.

[StringJunky]

What is the difference? Matter has mass.

 

All matter has mass but not all Mass is matter.

Edited September 18, 2011 by StringJunky

[csmyth3025]

All matter has mass but not all Mass is matter.

To expand on StringJunky's comment, the following may be helpful:

 

Under the "quarks and leptons" definition, the elementary and composite particles made of the quarks (in purple) and leptons (in green) would be "matter"; while the gauge bosons (in red) would not be "matter". However, interaction energy inherent to composite particles (for example, gluons involved in neutrons and protons) contribute to the mass of ordinary matter.

 

-and-

 

...definition of ordinary matter is more subtle than it first appears. All the particles that make up ordinary matter (leptons and quarks) are elementary fermions, while all the force carriers are elementary bosons.^[57] The W and Z bosons that mediate the weak force are not made of quarks or leptons, and so are not ordinary matter, even if they have mass.^[58] In other words, mass is not something that is exclusive to ordinary matter.The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see dynamics of quantum chromodynamics) and these gluons fields contribute significantly to the mass of hadrons.^[59] In other words, most of what composes the "mass" of ordinary matter is due to the binding energy of quarks within protons and neutrons.^[60] For example, the sum of the mass of the three quarks in a nucleon is approximately 12.5 MeV/c², which is low compared to the mass of a nucleon (approximately 938 MeV/c²).^[56][61] The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.

(ref. http://en.wikipedia....tons_definition )

 

I could have just provided the link, but I really like the colors they used in the graphic.

 

There's an old song entitled "Dust in the Wind" (Kansas, 1977) with the refrain "...all we are is dust in the wind..." Modern science tells us that we're actually about 1.5% "dust" and 98.5% energy. Kinda blows your mind, don't it?

 

Chris

[DrRocket]

All matter has mass but not all Mass is matter.

 

You now have the unenviable task of formulating a precise definition of "matter'. Good luck.

[StringJunky]

You now have the unenviable task of formulating a precise definition of "matter'. Good luck.

 

Before consulting WIKI I would have said that which occupies space and has the the property of mass but in reality, it would seem, is a quite grey term that has meaning depending on the context and field of physics it's used in:

 

The term "matter" is used throughout physics in a bewildering variety of contexts: for example, one refers to "condensed matter physics",[42] "elementary matter",[43] "partonic" matter, "dark" matter, "anti"-matter, "strange" matter, and "nuclear" matter. In discussions of matter and antimatter, normal matter has been referred to by Alfvén as koinomatter.[44] It is fair to say that in physics, there is no broad consensus as to a general definition of matter, and the term "matter" usually is used in conjunction with a specifying modifier.

 

So, no I can't give you a universally applicable definition of "matter"...I'm sure you would do a much better job than I.

[forumreader]

Energy is something intangible but have power.