
Physics Has Demoted Mass - AliCollins
http://nautil.us/issue/54/the-unspoken/physics-has-demoted-mass
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SAI_Peregrinus
It's very helpful to use natural units (or QCD units) when working with
particle physics. Set the speed of light, the reduced Planck's constant, and
Boltzmann's constant equal to 1. For QCD units also set the mass of the proton
equal to 1. Then compute all the other units based on this. (There are several
other systems of "natural" units also in use. All of them set the speed of
light to 1, but differ in what other units are included.)

A particular advantage to intuition comes with the famous e=mc^2. Since c is
1, and 1^2 is 1, e=m. Energy and mass are completely equivalent. Strong force
binding energy in a proton is mass. The only bit that's not straight from
binding energy is from the Higgs mechanism, which is where the mass of the
electron (and the quarks themselves) comes from. Matt Strassler has an
excellent explanation of that: [https://profmattstrassler.com/articles-and-
posts/particle-ph...](https://profmattstrassler.com/articles-and-
posts/particle-physics-basics/how-the-higgs-field-works-with-math/)

~~~
davidmanescu
Equalities that involve units aren't straightforward. Not a physicist of any
sort but don't all the 1's still fundamentally change the equality since they
change the units? I would guess they therefore implicitly change the intuition
behind these equations?

~~~
psyc
I would say it's the opposite. A unit conversion is not fundamental at all,
but a matter of arbitrary convention. 0C and 32F are exactly the same
temperature. Mass and energy are exactly the same property. c^2 is a constant,
so E doesn't even vary as the square of anything - it's just a linear unit
conversion. If you follow it further, you find c is only even in there because
some other units are defined in terms of it. That is, the ME equivalence
doesn't really have anything to do with the speed of information propagation
per se - but our chosen unit conventions do.

It's because of people's fondness for legacy and backwards compatibility that
we don't use natural units all the time, and still write "e=mc^2". I find this
insane, personally, but that's just the way it goes.

I guess I should add that apparently this is still controversial? But in my
mind, the only reason for this is that people find meaning in units. In this
case, ME being the same property implies duration being exactly the same as
length, which implies spacetime is a unified, regular 4D manifold. ME _not_
being the same property implies time is special. I've been fully persuaded
that duration is fundamentally exactly the same thing as length, so I've
chosen my side, in case there's any serious controversy.

~~~
jessriedel
Mass and energy are not the same property at all. E=mc^2 is only applicable at
the limit of zero speed.

~~~
jschwartzi
...In the same frame of reference as the observer.

------
ComputerGuru
I love reading about quantum mechanics at all different levels, and have read
and appreciated articles well beyond what I could properly comprehend in
fullness; but _man_ was this article all over the place.

I've never seen an author use metaphors or similies so poorly before. To draw
parallels between something hard to grasp and something made up and vaguely
defined in an effort to explain the former is.. ill advised at best. Then
there's the fact that the author spends forever to explain basic chemistry
then jumps into color charge in such a way that anyone not already intimately
familiar with at least the terminology of quantum physics would never be able
to understand, then the author jumps from topic to topic seemingly in a race
to drop references to as many different concepts as possible without actually
explaining any of them, almost like a student writing an essay then going back
and swapping words with a thesaurus to seem better informed.

Even the science aside, the writing itself is rather atrocious. The author
"answers" mysteries he never even asked or previously posed, and expects
readers to already know what he's trying to say so he can refer to that in his
explanations of why he said it.

Then the author has a tendency to jump from field to field, converting apples
into oranges with the help of a long-dead scientist only so he can add them
together in the most basic way and then convert them back to apples again. But
he got to prove that he knows of Avagdro, so obviously there's that.

Usually Nautilus articles are written much better than this. If you value your
sanity or actually care to understand the topic discussed, do yourself a favor
and look elsewhere.

~~~
hamilyon2
I respectfully disagree. He is imprecise, metaphorical, and offers
entertainment, rather than knowlege.

And jet, he knows his reader very well, and he delivers important bits of
knowlege in very digestable form. Sure, this is not a substitution for reading
a book.

But his target audience will never read that book, nor perform any research on
their own.

Now i firmly remeber what QCD exist and firmly believe I don't know what it is
about. Isn't it good, by itself?

------
ars
For some reason people are still caught up in finding some difference between
mass and energy.

There is no difference. They are two words that mean the same thing.

There are different _kinds_ of mass-energy, some types are easy to convert
into others, some types move at the speed of light, some don't. But there is
nothing distinguishing mass from energy.

It was a revelation to see photons attracted by gravity - but once you realize
it's energy that has a gravitational field [not just the particles we call
mass], it would be surprising if photons were not attracted by gravity.
(Although photons moving only at the speed of light have different equations
governing their motion under acceleration.)

Now, all that said,

There is a distinction between things that only move at the speed of light,
and things that never do. But the words energy and mass [as commonly used] do
not properly fit those two categories.

~~~
dukwon
Meanwhile, in real physics, there's a well-defined difference between the norm
of a vector and one of its components. Mass is Lorentz-invariant, energy is
not.

~~~
ars
> Mass is Lorentz-invariant, energy is not.

That's not completely accurate. Chemical energy and binding energy are also
Lorentz-invariant.

The only type of energy is not Lorentz-invariant is velocity energy, so you
are putting your distinction in the wrong place.

On top of that, there are other violated invariants.

The weight of a lump of iron near a magnetar is greater than the weight of the
same lump of iron near an identically massing neutron start.

This is because the potential energy of the iron is greater near the magnetic
field, so its mass (as seem by the magnetar) is greater, and so is the
gravitational attraction between them.

This means you can't just say "No velocity, the mass is identical", it's not -
the extra potential energy means extra mass.

Or in other words there is no such thing as mass as distinguishable from
energy.

~~~
evanb
I haven't thought about it carefully, but since magnetic fields don't do work,
my initial reaction to your example of iron near a magnetar is surprise. But,
I also expect that the iron magnetizes in a strong field. Wouldn't that be
lowering its energy (compared to an unmagnetized lump in a background field),
however?

~~~
ars
It's not a conservation of energy question, obviously you would have to deal
with the energy of getting it there in the first place.

The question is once it's there: Do the magnetar and the neutron star see
different masses for the lump of iron?

Imagine the magnetar and the neutron star at the tips of an L, and the iron at
the vertex.

------
dude01
I was just explaining to my teenage son what quarks are -- he hadn't learned
about them yet. So I have to upvote this.

tl;dr If you decompose matter all the way down, mass doesn't just "add up the
parts to the whole". Not by several orders of magnitude!

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cyberfart
Veritasium had a video explaining this a few years back, it's one of the
videos responsible for sparking my interest in physics and cosmology.

[https://www.youtube.com/watch?v=Ztc6QPNUqls&feature=youtu.be...](https://www.youtube.com/watch?v=Ztc6QPNUqls&feature=youtu.be&t=4m47s)

------
rurban
I would rather describe as a very weak, long-ranging, attracting force.

A force of a very special kind, because all other forces are strong, short-
ranging (they need to interact, the only not-mechanical force) and repelling.

~~~
davrosthedalek
Sorry, but that's quite wrong:

We have gravitational, weak, e/m and strong interaction.

Electromagnetic has the same range, only most objects seem to be neutral.

"Mechanical" force is normally electromagnetic.

The weak force is weak, but not as weak as gravitation (assuming normal
charges)

The strong force has indeed short range but is attractive.

~~~
evanb
Indeed, the reason most objects seem to be neutral is because of how strong
the electromagnetic force is! Were it weaker it would be much easier to
separate charges on longer length / time scales.

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angry_octet
"But what is matter, exactly? Imagine a cube of ice, measuring a little over
one inch (or 2.7 centimeters) in length."

Gasping. For. Air.

I love that an article on units gets a unit conversion massively wrong.

~~~
angry_octet
Touched a raw nerve obviously.

Lost due to use of imperial units: 1998 Solar Heliospheric Observatory 1999
Mars Climate Orbiter

------
mirimir
I mean, sure, mass is energy. We all know that. And still, this is a great
article. It ties together many concepts that I've read about.

------
averagewall
The conclusion that energy is more fundamental or easier to have an intuition
for has been the case since, what 100 years ago? It certainly was when I
studied physics 20 years ago.

But he doesn't need to go into quarks for that. Simply comparing the masses of
protons and neutrons (+ electrons) to the mass of an atom shows they're
different. There's a little bit less mass due to the lower energy of the bound
nucleons. Quarks certainly make the effect more dramatic though.

A more practical objection to using mass is that nobody can agree on what the
word means. Does a photon have mass? Yes or no, depending on if you're
thinking of relativistic or rest mass. If you call it energy, there's no
ambiguity.

If I could recommend he change anything though, it would be the horrible
mixture of units - MeV/c^2, atomic mass units, and grams. The author surely
has the time to convert them all to the same unit so the reader can easily
compare them. That would eliminate the need to explain Avogadro's law. It's a
completely redundant complication of chemistry and has nothing to do with the
fundamental concepts he's focusing on.

~~~
davrosthedalek
There is a difference though: A hydrogen atom is slightly lighter than it's
constituents. That's why it is stable. However, the nucleons are much, much
heavier than the sum of the quark masses. Which is strange, because it means
that naively, the unbound state should be preferred. But it isn't, instead,
you have confinement!

