
Why is light so fast? - aaronbrethorst
http://aeon.co/magazine/science/the-universal-constants-that-drive-physicists-mad/
======
msravi
Reading these articles about light and quantum theory is always a frustrating
experience for me. They are all invariably hand-wavy and never seem to explain
things from first-principles. Does anyone have a good reference for a book
that does justice to the subject?

On a related note, Simon Singh's book on the Big Bang Theory
([http://www.amazon.com/Big-Bang-Universe-Simon-
Singh/dp/00071...](http://www.amazon.com/Big-Bang-Universe-Simon-
Singh/dp/0007162219)) was the first book I read that explored the Big Bang in
great detail without being hand wavy. I wish he'd write a book dealing with
quantum theory!

~~~
logicallee
>They are all invariably hand-wavy and never seem to explain things from
first-principles.

For first principles, you'll need to talk to the designer - scientists only
have runtime profilers and guesswork. Even the guesswork isn't complete -
there's no unified theory
([https://en.wikipedia.org/wiki/Theory_of_everything](https://en.wikipedia.org/wiki/Theory_of_everything))
so it is kind of weird to ask everything to trickle down from first
principles, IMO.

~~~
sowbug
It's not weird; it's more that it depends on the answers to unanswered
questions that have been perplexing many people for a long time.

Maybe "premature" is a better description?

------
shepardrtc
I'm not a physicist, but from my understanding, light doesn't move at any
speed from its own point of view. Its actually instant. From creation to
absorption (or dissolution?), there's no delay from its point of view. Fast or
slow has no meaning for light. We view things as having speed because mass
slows things down from being instant. Am I correct?

~~~
redacted
(Disclaimer: I am a physicist, but this is not my area of expertise _at all_.
Happy to be corrected here).

Relativity is, like quantum mechanics, a fairly simple concept with incredibly
complex implications and edge cases.

The easiest intuitive explanation of relative time I have found is the
following:

\- Assume our space time/universe is a 4D vector space. Three spatial
dimensions, one time.

\- Everything has a 4D vector which describes movement through this 4D space-
time {x, y, z, t}

\- The length/magnitude of this vector is fixed at the speed of light, c

\- Normalize the dimensions of our 4D space as following: if we are not moving
at all (x = y = z = 0) the vector points entirely in time our vector is {0, 0,
0, c} and, in our frame of reference, time moves as normal - "one second per
second".

\- Now, as we go faster and faster this vector no longer points purely in
time. In the extreme case where the vector sum of the x, y, z (3D spatial
component) is c, the time component t will be zero. This is why our photon
does not experience time passing - it moves through space at c, so cannot move
through time at all.

For the 3D velocities we normally experience we do not move in space fast
enough to affect motion through time appreciably. Even the GPS corrections for
relativity mostly arise due to Earth's gravity well distorting local space-
time geometry, although their high velocity does contribute.

Objects with mass cannot be accelerated to c under our current understanding
of relativity because kinetic energy diverges (approximately
1/sqrt(1-v^2/c^2)) - reaching speed of light would require infinite energy.

------
astrobe_
> "Observations of astronomical bodies under gravity do not show this
> decrease, and so far there is no sign that G varies in space"

Correct me if I'm wrong, but observations _do_ show there's a significant
problem with the equations, which led to the invention of "dark matter" and
"dark energy".

Aside from that, is there any connection between the universal constants of
physics and mathematical constants? It would be nice to be able to say, "The
Universe is the way it is because circles."

~~~
dogma1138
Dark matter and energy are there to solve an issue with the cosmological
constant which is a "value" that was introduced by Einstein to make his
general theory of relativity work with the back was accepted as a static
universe, basically it's the energy density of the vacuum in space. This
constant was then "abandoned" after Hubble discovered that the universe is
expanding, it was still there but it's value was (assumed to be) zero.

When the scientific consensus reached a point where it was agreed on that the
universe is accelerating the cosmological constant came back into play because
with it you can explain the accelerated expansion, the problem is that we
can't account for the additional energy needed to account for the acceleration
so dark energy was introduced as a concept.

Dark Matter was introduced to solve another issue, one that can be seen on
much smaller (or own galaxy) scales, basically if we look at the motion of
stars and the rotation of galaxies we seem to be lacking mass, and quite a bit
of it (although not nearly as much as dark energy) so again a place holder
device was introduced in the form of dark matter

Now normally you would say well when you need to introduce additional doodads
to account for something in your theory not in 1 instance but in 2 and maybe
in many others your theory sucks. The problem is that we've sorta proven that
gravity works for the most part as we think it does, and if we go into weird
stuff like localized gravitational constants well they don't account for the
observations that required dark matter or energy, oh and they kinda break the
universe.

The force of gravity and hence the gravitational constant has been proven to
be "correct" in from the smallest (even atom level) observations and
calculations to the macro and universal scales, and while it's true that we
might be wrong, if we are we are wrong by not a mile but probably several
parsecs this means that relativity and other current accepted gravitational
theories are more wrong than the "Ether Theory".

~~~
zamalek
> more wrong than the "Ether Theory".

They are locally correct, just like Newton's theories were correct up until we
observed Mercury.

That being said I'm 99% in agreement with mainstream science: Einstein's work
just makes too much sense to be wholly incorrect. Where I'm in strong
disagreement with mainstream science is outright hacks where they turn dark
matter/energy into real things (e.g. WIMPs). Non-constant G is a more
worthwhile avenue than that IMO.

~~~
imglorp
The curious thing is the trouble spots have been mapped. There are filaments
and voids where the gravitational effects of unseen matter/stuff are plainly
observable: something is there pulling on stuff. MOND is not enough to answer
that.

~~~
zamalek
Possibly I didn't make my arguments correctly.

> MOND

I'm not saying that MOND is correct at all, I'm saying that we believed that
classical Newtonian dynamics was seen as correct at one point - just like SR
is seen as correct now. My opinion is that it's highly unlikely that SR is
incorrect (or partially incorrect), however, I do see it as a remote
possibility.

> There are filaments and voids where the gravitational effects of unseen
> matter/stuff are plainly observable

Another way of looking at it is a map of the sum of things that we don't know.
Again, using Mercury as an example, we were able to calculate the [sum of]
force the was "wrong." The dark matter map is incredibly cool because it's the
same thing done on a unbelievably massive scale. There were certainly people
who believed that this unaccounted-for force on Mercury was a single force
with a trivial explanation. We now know that this was not the case.

That is, in my opinion, the same mistake we are now making - simply because we
can _calculate_ a map of the effect does not mean that it's actually a map of
real stuff.

Although I'm in disagreement with MOND I do think it does something right: the
μ function. "This is something that we don't know." In the same way it is in
my opinion that dark matter and dark energy are merely unknown functions and
not "real matter" and "real energy." I certainly think that Turner and Zwicky
had the same thought pattern when they coined the terms.

~~~
dogma1138
MOND is quite interesting indeed (been to a couple of Mordechai lectures about
this subject), the only problem is that it can't be used to construct a
functional universe under TeVeS stable stars couldn't form.

Sadly Jacob Bekenstein died just a month ago and I'm not sure how much work
will be done on MOND now.

------
ctdonath
In the time it takes for light from this (your) screen to reach your eyes,
this (your) CPU just carried out a dozen instructions.

Why is light so slow?

~~~
sunstone
Sure, but from the frame of reference of the light it takes no time at all.

------
vorg
> Are some [constants] more fundamental than others? [...] one useful choice
> has been just three: h, c and G, collectively representing relativity and
> quantum theory. In 1899, Max Planck, who founded quantum physics, examined
> the relations among h, c and G and the three basic aspects or dimensions of
> physical reality: space, time, and mass.

I thought there were 5 "Planck units" (h, c, G, the electron charge, and
Boltzmann's constant) matching 5 dimensions of physical reality (space, time,
mass, also charge and temperature). But I don't understand two things:

* Why is Boltzmann's constant there, temperature being a statistical property more akin to the fine structure constant than the other 4 Planck units?

* Why do physicists nowadays prefer to use the electron charge instead of Coulomb's constant as Planck did? Coulomb's constant and the gravitational constant G slot into similar looking formulas for electromagnetism and gravity respectively, and pairing them seems more "fundamental" than using the electron charge.

~~~
xahSooJu
> [...] matching 5 dimensions of physical reality (space, time, mass, also
> charge and temperature).

I'm not quite sure I understand that, but I'll try to answer your questions
anyway:

Yes, Boltzmann's constant is more or less just a conversion factor between
temperature and energy. If we measured temperature in joules, we wouldn't need
Boltzmann's constant. But then the same is true for c; we could measure time
in meters or distance in seconds.

If you have defined the basic units of mechanics (time, distance, and mass),
the value of G is fixed. But not the value (and even the dimension!) of
Coulomb's constant and of electric charges. You can use a system of units
where Coulomb's constant is 1 and electric charge then has dimension
mass^(1/2) _length^(3 /2)_time^(-1), while in SI units it has dimension
current*time. Basically, you can make Coulomb's constant have any value and
any dimension you want. Using just Coulomb's constant or just an electric
charge in such a formula wouldn't make much sense. On the other hand,
something like the fine structure constant (which is practically the square of
the elementary charge measured in natural units) is a quantity that makes
sense inpendently of your system of units.

I guess the reason for that is that mass has meaning outside of gravity (in
Newton's second law), but electric charge is confined to electromagnetism.
There's also the thing with electric charge being quantized to integer
multiples of the elementary charge e (apart from quarks for which it is an
integer multiple of e/3, but they usually don't appear isolated), but mass not
being quantized.

I think the similarities between electromagnetism and gravity are at least
partly superficial. Coulomb's law looks a lot like Newton's law, but that's
because both the electrostatic and the classical gravitational potential obey
a poisson equation (in the statical limit and to the lowest order). And that's
about the simplest equation such a potential can obey. I don't think there's
much more to it than that (perhaps apart from both being long-ranged because
their symmetries are not broken).

~~~
vorg
> both being long-ranged because their symmetries are not broken

I guess this is the property of both that appears similar, and it just seems
more than coincidental that two of the four (or five) fundamental constants of
nature describe these at least partly similar interactions.

------
kazinator
> _But some constants involve no dimensions at all. These are so-called
> dimensionless constants – pure numbers, such as the ratio of the proton mass
> to the electron mass. That is simply the number 1836.2 (which is thought to
> be a little peculiar because we do not know why it is so large). According
> to the physicist Michael Duff of Imperial College London, only the
> dimensionless constants are really ‘fundamental’, because they are
> independent of any system of measurement. Dimensional constants, on the
> other hand, ‘are merely human constructs whose number and values differ from
> one choice of units to the next’._

Say what?

Unitless constants are exactly the same stuff as dimensional constructs; it's
just that the units canceled out. You measure a proton's mass in some
arbitrary units, the electron in the same units and when you divide the two,
the units go away. This does not create a philosophically distinct category of
constant.

~~~
rrss1122
I think it does. Whatever our choice of units (provided you use the same
choice of units in all calculations), the ratio of mass of the proton to the
electron will be the same. This is what makes the constant fundamental: it is
independent of any way we choose to measure it, so should be the same to
anybody and everybody. If we were to meet an alien civilization and study
their physics, as long as we know their number system, we would immediately
recognize the number 1836.2.

~~~
kazinator
> _If we were to meet an alien civilization and study their physics, as long
> as we know their number system, we would immediately recognize the number
> 1836.2_

Only if that number really is a constant, so that it matches in their pocket
of the universe. For sure-fire mutual recognition of numbers, I would stick
with something mathematically defined, like some large-ish prime numbers, pi,
e, and so forth.

> _the ratio of mass of the proton to the electron will be the same._

In effect, the electron's mass is then the unit of measure. A proton's mass is
1836.2 electrons, and so many kilograms, do many ounces, etc.

------
mentos
What is contained in a cubic meter of the vacuum of space?

~~~
elektromekatron
Everything going through it plus some noise.

~~~
mentos
Do things 'go through' the vacuum of space or is it like newton's cradle where
the fundamental building blocks just bump shoulders yet do not move?

So for example when light travels from a million light years away, is it one
fundamental particle traveling through space. Or are there trillions of
interactions passing energy along?

~~~
pavel_lishin
> _Do things 'go through' the vacuum of space or is it like newton's cradle
> where the fundamental building blocks just bump shoulders yet do not move?_

You mean, is motion an illusion, much like a glider in Game of Life seeming to
move?

~~~
mentos
Yea, are we just living in an enormous three dimensional grid or are there
true vacuums in space?

~~~
elektromekatron
One thing to consider, is that given rate of change approaches zero as
velocity approaches c, what does motion mean when there is no time for it to
happen in, either as things moving or bumping?

------
jameshart
Because it's really light? (sorry).

Seriously, though, what does it mean to ask "Why is light so fast?" \- are you
looking for some purpose in light traveling fast? You won't find one. It just
DOES.

In fact, given that the much simpler alternative to there being a speed limit,
c, on the universe would be that there is NO speed limit, then the question
really becomes, why is light so SLOW?

~~~
rrss1122
The article does ask this:

"Why not faster? Why not slower?"

Certainly a lot of physicists are content with leaving it at "because it is."
They're not searching for purpose, they're searching for explanation. The
article doesn't just ask the question either, it explores a possible avenue
for seeking the answer.

Experiments over the past few years seem to indicate that the speed of light
can be derived by measuring electric and magnetic properties of the vacuum.
This leads to the question: is it possible that the speed of light is the
value it is because the vacuum restricts it to this value? This would mean the
speed of light is not a fundamental constant, but an observable parameter of
the vacuum.

The article is light on links, but here is a paper that I think the article
was referring to, by Marcel Urban and colleagues at the University of Paris-
Sud:

[http://arxiv.org/abs/1302.6165](http://arxiv.org/abs/1302.6165)

From the paper:

"When a real photon propagates in vacuum, it interacts with and is temporarily
captured by an ephemeral pair. As soon as the pair disappears, it releases the
photon to its initial energy and momentum state. The photon continues to
propagate with an infinite bare velocity. Then the photon interacts again with
another ephemeral pair and so on. The delay on the photon propagation produced
by these successive interactions implies a renormalisation of this bare
velocity to a finite value.

This “leapfrog” propagation of photons, with instantaneous leaps between
pairs, seems natural since the only length and time scales in vacuum come from
fermion pair lifetimes and Compton lengths."

The paper claims that the speed of light might fluctuate as a consequence, and
proposes possible experiments to test this.

"The propagation of a photon being a statistical process, we predict
fluctuations of its time of flight of the order of 0.05fs/√m. This could be
within the grasp of modern experimental techniques and we plan to assemble
such an experiment."

This could answer the question, why is light so slow?

~~~
vorg
This explanation still leaves open the question "why is gravity no faster than
light?"

------
rndn
Relative to matter? Photons are massless, so light doesn't get slowed down by
interacting with remote particles as it travels.

Relative to humans? Humans are made of matter, and in addition to that, they
are immensely complex bio-chemical mechanisms and depend a lot on slow
stochastic processes such as diffusion, so a lot of other processes will
appear fast to them.

~~~
qwertyboy
From reading the article (and not enjoying it very much - see msravi's comment
about its handwavyness), the question it's failing to answer isn't "why is
light faster than X" but rather "why is the speed of light as it is".

~~~
stan_rogers
In a lot of ways, _that_ question is just about as meaningful as "why are
there electrons?" Looked at from the right angle, you can say that there is
only one speed at which _everything always_ moves through space-time; the only
difference, really, among speeds is how much of that speed extends timewards
from the moving thing's perspective. (What space-time itself gets up to, and
what it _is_ apart from something we experience, is a different set of
questions altogether.) The idea that we ought to be able to understand
everything in principle is a horse long out of the barn.

~~~
JoeAltmaier
Its definitely an interesting question. Something that limits all, moves
uniformly no matter the point of view, doesn't interact with itself but does
with everything else - its a singular feature of physics.

If I understand you right, one can wonder things like, maybe 'light' is really
'time' in some sense, not moving uniformly but instead the actual clock that
drives the universe. Stuff like that is, at the least, interesting fodder for
bull sessions.

------
amelius
So if the vacuum contains quantum fluctuations in which particles are being
produced, I wonder what the mathematics looks like. How is the creation of a
singular point-like element (or a pair of them) modeled mathematically?
Roughly sketched of course :)

~~~
IsTom
It's not really particles. [http://profmattstrassler.com/articles-and-
posts/particle-phy...](http://profmattstrassler.com/articles-and-
posts/particle-physics-basics/virtual-particles-what-are-they/)

~~~
gaze
But it is. I can have devices that use single electrons. I can measure shot
noise. Theories in terms of particles work. Turns out that theories in terms
of off-mass-shell particles describing higher and higher terms of perturbation
theory work well too.

------
callesgg
I like to think of light as a something we made up in our minds.

A light bulb that is illuminating a wall is actually more like the light bulb
touching the wall, rater than it sending out light that is hitting the wall.

