
Excitement Over Gravity Waves Comes Crashing Down - dnetesn
http://nautil.us/blog/scientists-excitement-over-inflation-comes-crashing-down
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trhway
>These swirls would bolster the idea that the infant cosmos expanded faster
than the speed of light during a brief growth spurt called inflation.

what speed of light they are talking about - today's one or the one that was
ruling Universe back then? Physical constants do change with changes in the
Universe (otherwise the visible Universe which was long time ago inside its
current Schwarzschild radius - 10B in today's dollars ... err ... light years
- would have supposedly crossed it to get to grow to the 46B light years the
Universe is today. Either it crossed the Schwarzschild radius or the
Schwarzschild radius of the same visible Universe was "deflated" back then and
got inflated together with the Universe inflation - that means physical
constants change. Actually the constants may be the same - for the speed it is
just length of the different, "deflated", space divided by the different,
"deflated", time)

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guygurari
The speed of light is a dimensionful quantity -- it has dimensions of length
over time. Dimensionful quantities cannot be measured, only dimensionless ones
can be measured: we can only measure pure numbers.

When we say we measure the speed of light, we are really measuring the ratio
between that and some other arbitrary speed defined by our measurement device.
Therefore, it makes little sense to ask how the speed of light changes over
time; we can only ask this question after we specify how we measure, and then
it's no longer a fundamental question.

~~~
HCIdivision17
It may be a bit surprising that the speed of light is actually a consequence
of universal constants interacting, and not merely measured via reference
benchmarks [0]. At least for me, finding that Maxwell's equations distill an
equation that happens to be a velocity in a vacuum was extremely gratifying.
There's a notion that perhaps if the constants were different, then _c_ would
be different as well - both in scale and even dimensionally; this is, I think,
what the parent is referencing.

EDIT: I'd like to restate why _c_ is neat. There's a lot of history to it, but
it's sort of a form of a number ending up so important that it overtook the
archetypical "and a constant c". I _highly_ recommend the article from Phillip
Gibbs that goes into this in depth [1]. Your comment actually shows up near
the beginning of the long answer in the form of paragraph 5 of The Long
Answer, so you'll likely enjoy the additional detail.

[0]
[http://en.m.wikipedia.org/wiki/Maxwell's_equations#Vacuum_eq...](http://en.m.wikipedia.org/wiki/Maxwell's_equations#Vacuum_equations.2C_electromagnetic_waves_and_speed_of_light)

[1]
[http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLigh...](http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/c.html)

~~~
guygurari
These universal constants (vacuum permittivity and permeability) are
themselves dimensionful quantities, so the same comment applies to them. They
can only be measured by comparing to a reference, and there is no natural
sense in which they can be said to change over time.

By the way, these constants are no more 'universal' than the speed of light
itself.

~~~
HCIdivision17
I mean, sure, it's going to be turtles the whole way down if you're looking to
define the universe without resorting to physical quantities (that is,
dimensioned units). We don't have anything like a Grand Unified Theory yet,
wherein we define Physics by means of some elemental mathematics (in the form
that we can bootstrap computation from lambda calculus via things like the Y
Combinator [0]). Besides, we occasionally give dimensional names to
dimensionless quantities (my favorite being the engineering unit the inverse
radian) [1]. It's a useful abstraction, and it seems confusing to complain
about it.

So we resort to what we know, which is what we see. We can't see more than the
surrounding universe, but we can try extrapolating from what seems to work.
Attempting to stifle that inquiry seems a bit... I dunno, pointlessly
antagonistic.

This article shows science in action, doing what it does best: taking
observations and reconciling them with other observations via theory, and then
fixing theory to match. It _seems_ our universe follows certain equations
which are themselves dimensionful, so I'm not sure why we wouldn't attempt to
benchmark the universe against itself - we don't have much else to use. Even
dimensionless numbers are only marginally useful, like alpha; it may "exist"
and manifest as our universe, but it's not especially predictive.

[0]
[https://www.youtube.com/watch?v=FITJMJjASUs](https://www.youtube.com/watch?v=FITJMJjASUs)
(one of my favorite videos - I _still_ don't grok it, but I'm getting closer!)

[1] [http://arxiv.org/pdf/1409.2794.pdf](http://arxiv.org/pdf/1409.2794.pdf)

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idlewords
I agree with the last quote in that list. This is a really wonderful example
of science working the way it's supposed to.

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z3t4
Sometimes I wonder if ppl actually know there's more stuff in the world then
what the eye can see.

Like that there's more stuff in the universe, then just the glowing stars.

