[ 3 / biz / cgl / ck / diy / fa / ic / jp / lit / sci / vr / vt ] [ index / top / reports ] [ become a patron ] [ status ]
2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

View post   
File: 43 KB, 500x467, 43 WTF.jpg [View same] [iqdb] [saucenao] [google]
1578119 No.1578119 [Reply] [Original]

WHAT
IS
ENERGY?

There, I asked you the most abstract question in the universe.

>> No.1578127

Sorry.
>There, I asked you the most abstract question in the universe.
Should be.
There, I asked you the most abstract question known to man.

>> No.1578130

It's another form of matter

>> No.1578136

>energy is everything

inb4 etc

>> No.1578139

>>1578130
this

>> No.1578144

sugar!!! its fucking sugar!!

>> No.1578156

Energy is the quantity that is conserved because of invariance under translation in time.

>> No.1578157

>>1578130
>>1578139

Fuck off with your begging the question fallacy.

>> No.1578161

a number that you calculate based on certain measured physical quantities

>> No.1578163

>>1578156
That's not the answer to what it is.

>> No.1578175

>>1578163
It is, actually.
(I can understand very well that you don't like the answer)

>> No.1578181

>>1578175
Dear god, because it is something that stays constant over time, flowing in different forms constantly, doesn't say WHAT it is.
You've only described how it works.

>> No.1578182

>>1578163
It is actually.

>> No.1578187
File: 228 KB, 852x478, Fuckingmagnets.jpg [View same] [iqdb] [saucenao] [google]
1578187

>>1578181
>Implying physics is about WHAT things are not how they work.

HINT

It's fucking magnets HOW DO THEY WORK?
Not fucking magnets WHAT ARE THEY?

>> No.1578194

>>1578156
>>1578175
>>1578182
Explain why the same thing couldn't be said about momentum.

>> No.1578199

>>1578194
Momentum <span class="math">\leftrightarrow[/spoiler] invariance under spacial translation

>> No.1578203
File: 11 KB, 244x343, Noether.jpg [View same] [iqdb] [saucenao] [google]
1578203

>>1578194
But it can, because of Noether's theorem.

Problem?

How do you define what momentum "is"?

>> No.1578206

>>1578187
>Implying we fully understand the flux
>Implying we know how magnets work
>Implying knowing WHAT something is, isn't essential

How can you even begin to have any slight idea about something when you can not form a concrete image about the thing you're studying?

>> No.1578208

>>1578203
Then energy AND momentum are both "the quantity that is conserved because of invariance under translation in time"?

>> No.1578210

WHAT IS CHAIR!

>> No.1578213

energy is the capacity to do work.

Saged, reported

>> No.1578216

>>1578208
energy - time
momentum - space
charge - gauge
angular momentum - rotation

>> No.1578225

>>1578216
Well, but >>1578203 basically said that momentum is also invariant under translation in space. Is it, or is it not?

>> No.1578227

>>1578225
> translation in space
should read "time"

>> No.1578228
File: 77 KB, 799x550, 1270056559369.jpg [View same] [iqdb] [saucenao] [google]
1578228

Energy is a measure of the potential to reverse entropy.

>> No.1578231 [DELETED] 
File: 112 KB, 331x398, James_Clerk_Maxwell.png [View same] [iqdb] [saucenao] [google]
1578231

>>1578206
>Implying we fully understand the flux
>Implying we know how magnets work
<span class="math">\nabla \cdot \mathbf{E} = \frac{\rho}{\epsilon_0}[/spoiler]
<span class="math">\\nabla \cdot \mathbf{B} = 0 [/spoiler]
<span class="math">\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}} {\partial t}[/spoiler]
<span class="math">\nabla \times \mathbf{B} = \mu_0\mathbf{J} + \mu_0 \varepsilon_0 \frac{\partial \mathbf{E}} {\partial t}\ [/spoiler]

>Implying knowing WHAT something is, isn't essential
It isn't to physics. I don't know what the EM field "is", except that it behaves according to Maxwell's equations. You could say that knowing how something behaves is knowing what it is. Sure. It is an entity with these properties. But can I define it in terms of other entities? No, not really.

>How can you even begin to have any slight idea about something when you can not form a concrete image about the thing you're studying?
Spin. Color charge. You try and form a concrete image of that.

>> No.1578237

WHAT
IS
LOVE?

There, I asked you the most abstract question in the universe.

>> No.1578240
File: 112 KB, 331x398, James_Clerk_Maxwell.png [View same] [iqdb] [saucenao] [google]
1578240

>>1578206
>Implying we fully understand the flux
>Implying we know how magnets work
<span class="math">\nabla \cdot \mathbf{E} = \frac{\rho}{\epsilon_0}[/spoiler]
<span class="math">\nabla \cdot \mathbf{B} = 0 [/spoiler]
<span class="math">\nabla \times \mathbf{E} = -\frac{\partial \mathbf{B}} {\partial t}[/spoiler]
<span class="math">\nabla \times \mathbf{B} = \mu_0\mathbf{J} + \mu_0 \varepsilon_0 \frac{\partial \mathbf{E}} {\partial t}\ [/spoiler]

>Implying knowing WHAT something is, isn't essential
It isn't to physics. I don't know what the EM field "is", except that it behaves according to Maxwell's equations. You could say that knowing how something behaves is knowing what it is. Sure. It is an entity with these properties. But can I define it in terms of other entities? No, not really.

>How can you even begin to have any slight idea about something when you can not form a concrete image about the thing you're studying?
Spin. Color charge. You try and form a concrete image of that.

>>1578208
Momentum in one direction is conserved if the laws of physics are independent of position in that direction. (x-momentum is conserved if nothing changes if everything moves in the x-direction). Energy is conserved if the laws of physics are independent of time.
>>1578225
>Momentum invariant under translation in space
>Implying momentum is a function of space coordinates and not an aggregate property of a system.

Lrn2 Lagrangian mechanics.

>> No.1578239

>>1578225
Emmy didn't say that.

>> No.1578245

>>1578239
So that other guy was spouting bullshit?

>> No.1578247

>>1578237
It's not the most abstract question in the universe if it isn't a statement in category theory, the branch of mathematics so abstract even mathematicians refer to it as "highly abstract nonsense".

>> No.1578255

>>1578245
Kind of, yes, but I think he just mixed something up.

>> No.1578256

Energy is a quantity that can be assigned to any particle, object, or system of objects as a consequence of its physical state

>> No.1578257

>>1578245
I'm that other guy, and no, I wasn't spouting bullshit, but maybe I wasn't 100 % clear. Emmy's little brilliant theorem says that if the laws of physics are independent of some variable, then there is a conserved quantity associated with that variable. If the variable is time, the quantity is energy. If the variable is a coordinate in space, it's momentum in that direction. If it's an angle the quantity is angular momentum. And so on.

>> No.1578263

>>1578256
Momentum can be assigned to particles too.

>> No.1578273

>>1578257
Your reply arguably implied that momentum<->time, that's where the confusion came from. Just forget about it.

>> No.1578274

>>1578255
>>1578257
Okay, because reading this I got the impression that energy = the quantity that is conserved because of invariance under translation in time, AND momentum = the quantity that is conserved because of invariance under translation in time.

You know, if that were the case, and you were on Jeopardy, and the answer was "This is the quantity that is conserved because of invariance under translation in time", you might lose depending on whether you say "What is energy?" or "What is momentum?".

But now that's sorted out.

>> No.1578279

>>1578263
So?

>> No.1578281

Maybe we need to clear up some terms.
A quantity is CONSERVED if its value doesn't change over time. The energy of a system doesn't change over time, so energy is a CONSERVED quantity.
The laws of physics are INVARIANT under some transformation if the transformation doesn't affect the form of the equations. (You can formulate it more formally with Lagrangians.) If you perform an experiment you should get the same result at one side of the room as on the other side, if all other conditions are the same. Then the laws of physics are INVARIANT under translation in that direction. If the result is the same in the morning as in the afternoon then the laws of physics are INVARIANT under time translation. (Of course it has to hold for any translation, but as examples...)

Noether's theorem states that for each invariance there is a conserved quantity.

>> No.1578289

>>1578273
Yeah I can see how you can get that impression now. I meant to refer to "the same could be said about momentum" in a more abstract sense, as momentum too can be defined as "the quantity that is conserved because X".

>>1578279
So how do you tell the difference between energy and momentum? Just saying it can be assigned to any particle isn't enough to separate out energy. It's like saying Germany is a country. Ok, it is, but which country is Germany? It's an accurate description but not a precise definition.

>>1578274
Yeah I can see why you were confused now.

>> No.1578300

>>1578289
Momentum is mass * velocity (* lorentz factor when dealing with relativistic speeds)

>> No.1578311

>>1578156
The momentum of an object at rest or moving at constant speed is also conserved under translation in time.

So obviously that's not enough to define energy.

>> No.1578331

>>1578311
See
>>1578281
The quantity momentum does not change over time. But momentum is the quantity associated with spatial translational invariance (the Noether charge).

>> No.1578569

>>1578331
space current = momentum
Haha. Nice way of saying it :)

>> No.1578576

energy is just a word. It doesn't have any units or anything.
Stuff like momentum, electron volts, current, and work are more what you're looking for.

>> No.1578647

>>1578576
>energy is just a word. It doesn't have any units or anything.
What about Joule?

>> No.1578665

Energy is the ability to use a potential.

Before you fuckoffs tell me about potential energy, try and fucking obaserve it, it is a mathematical construct.

>> No.1578686

>>1578647

Or for that matter, how about British Thermal Units, foot-pounds, or calories.

>> No.1578687

>>1578665
>potential different from potential energy
Wait what?

>> No.1578709
File: 35 KB, 527x747, richardfeynman.jpg [View same] [iqdb] [saucenao] [google]
1578709

Well the text book definition is "the ability to do work" where work is "Force = Mass * Distance", so in a nut shell, energy is just the ability to cause a change in something else really.

Although I'm going to give you the Richard Feynman description. I read this in a book called The Character of Physical Law a long time ago and will butcher the crap out of his analogy, but here goes.

Imagine a little kid has a bunch of blocks, and the mom is obsessed with keeping track of them. One day the mom counts too few blocks, but she notices the toy box is heavier so the missing blocks are accounted for. Another day, she notices her kids bathwater is higher and knows the blocks must be in there, so she can count them by measuring the bath water. Another day the toilet is stopped up and she has to get a plumber to fix it, the plumber finds blocks jammed in it and charges her $5 for each block, so now she can count the blocks based on the plumbing bill. Feynman then goes on to say that the blocks are like energy, except energy we cant see or touch, but we can measure it using a whole bunch of different means like the mom measured the blocks using weight, water, and money, without ever actually having to count or touch the blocks.

Basically what the analogy means, is energy is a real thing, but we can only see it by measuring the effects it has on other things that arent energy.

>> No.1578715

>>1578709

oops, "Energy = Force * Distance" fucked that bit up hard

>> No.1578726

Energy is a clever mathematical constructs that makes drawing connections between different observations easier.