
A Universe Made of Tiny, Random Chunks (2013) - dnetesn
http://nautil.us/issue/2/uncertainty/a-universe-made-of-tiny-random-chunks
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jamesdsadler
If the Planck length is Lorentz-invariant but macro-scale objects are not then
does that not imply there is a special universal reference frame against which
to measure velocity?

If I have understood the article correctly one would be able to measure the
length of a spaceship relative to the Planck length and deduce velocity,
entirely locally (i.e. onboard the spaceship).

This is a fundamental departure from general relativity which says there is no
special frame of reference.

~~~
vog
I guess this is simply one of the many incompatibilities between quantum
theory and general relativity.

There are many attempts to combine these theories into a universal theory (pun
intended), but it is hard to check the corner cases where those theories
differ. That's one of the reasons we build better and better particle
accelerators.

Either way, it doesn't make sense to apply (pure) general relativity to the
small scale, nor to apply (pure) quantum theory to the large scale. The
physicists know for decades about of that issue and are already taking care of
that.

~~~
dogma1138
Quantum Gravity is pretty coherent it can explain the universe we see today,
it can explain why an apple drops, and it can explain why galaxies form, it
cannot explain the big bang and some periods after it but neither can general
relativity.

For the most part particle accelerators are not needed to explain quantum
gravity, we do use them to find "new physics" but this new physics is more in
the lines of the known unknowns.

We also do apply relativity to small scales every day, without relativity
muons could not be discovered and without relativity to some extent even large
particle accelerators would not "work" because the effects of spatial
contractions are pretty important for how we predict and analyse the data
coming from particle accelerators especially the "messy kind" like the LHC.

As for the large scale stuff as mentioned earlier quantum gravity is pretty
compatible with general relativity in terms of explaining how the universe
that we see today looks and works, you can easily explain why and how the moon
rotates around the earth, it does rely on a massless spin-2 particle called a
graviton which is yet to be "discovered" and it does break if the graviton
would have a different spin (for example spin-0 graviton).

So I don't really understand the notion of why people still think that quantum
gravity and general relativity aren't compatible to the extent of "what the
fuck is going on", which is odd since afterall GR isn't 100% compatible with
the Standard Model either, since GR is background independent and does not
care about the particular state or shape of space-time while SM does.

~~~
vog
From your long statement I read that you agree with my criticism that one
should not use the plain quantum theory, mix it with the plain general
relativity, and wonder why this leads to contradictions. Of course it does! If
one wants a coherent model, one should use the Standard Model instead (or one
if its variants).

Not sure at which point you disagree with my statement, though.

~~~
dogma1138
Depends on what you define as GR, there are classical and relativistic
versions of Quantom Mechanics.

Each theory is useful for various things because each theory provides you with
certain tools and perspectives that are useful for performing specific tasks.

At the end every theory is a set of laws and abstractions you use theories to
change the perspective of how you look at things but these are often
abstracts.

You can look at particles as particles, waves or fields it doesn't change
reality but every one of these viewpoints comes with its unique benefits and
you can chose between them depending on what benefits you most to for a
specific task or a situation.

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haversine02
The idea that the Universe is this sort of discrete lattice always makes me
suspect simulation. I feel like true reality should not become grainy at some
point, it feels like a mark of artificial origin.

~~~
Razengan
Or you can simply think of it as the best "resolution" that macroscopic
instruments rooted in 3 dimensions can reduce it to.

I feel like the whole "wave-particle duality" is already a hint that the true
nature of reality may always remain outside of our observation capability.

In fact, I think that humans may be a little too biased towards picturing
everything as made up of discrete parts ("particles"), and that is probably a
byproduct of having visual eyesight. Can't wait to meet alien intelligences
with completely different senses and see what they think. :)

~~~
m12k
I read about this phenomenon where the two slit experiment could be replicated
with drops bouncing on an oil bath (here's an article on it:
[http://resonance.is/news/quantum-weirdness-replaced-by-
class...](http://resonance.is/news/quantum-weirdness-replaced-by-classical-
fluid-dynamics/) ). And one about how a higher-dimensional mathematical object
could dramatically simplify certain quantum mechanical calculation (
[http://www.wired.com/2013/12/amplituhedron-jewel-quantum-
phy...](http://www.wired.com/2013/12/amplituhedron-jewel-quantum-physics/) ).
I realize this proves nothing, but I'm still holding out hope that the
randomness we observe is just a result of the interaction that higher
dimensional "matter/energy" does when it intersects with our 3/4 dimensions.
Maybe god doesn't play dice after all, maybe there's just a whole lot going on
before we get to make our measurements.

~~~
dogma1138
This experiment is pushing towards Bohemian Mechanics, we all like PWT but I'm
not sure what does this has to do with the comment above :)

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amai
The article is based on a popular misconception: The Planck length is Lorentz
invariant, so special relativity must break down at Planck length scales.

However this is wrong. The Planck length is the minimal length of a 4-vector
(a 4-dimensional vector measuring the distance between two events in space-
time). But the length of a 4-vector is invariant under Lorentz transformation,
so it also doesn't Lorentz contract. So there is no conflict between special
relativity and a constant Planck length.

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dopu
This is some of the best pop-sci writing I've read in quite some time. Hat's
off to Carl Frederick; itching to go read some of his science fiction now.

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ajuc
> it’s the only length that can be derived from the constants c, G, and h
> without adding some arbitrary constant—so it may retain the same value in
> all reference frames, not subject to any Lorentz contraction. But the Planck
> length is derived from universal constants, so it must have the same value
> in all reference frames; it can’t change according to a Lorentz contraction.

The arbitrary constant is 1. How is 1 less arbitrary than 2, 42, or 3.14?

I don't get it - is it trying to say objects of Planck length wouldn't
contract due to relativity? If so - why?

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chriswarbo
1 is the multiplicative identity, i.e. x * 1 = x, hence we can always leave
out a "* 1" factor without changing things.

A different factor, like 2, is more arbitrary, since "* 2" can't be left out
without changing the value.

You can make the claim that a "* 1" factor is lurking in there, but even from
that perspective it's less arbitrary than "* 2", since we could claim that "*
2" also has a "* 1" lurking in it, and so on :)

~~~
ajuc
I mostly meant - how is this proving that object of length 1 * planck length
won't contract, and object of 2 * planck length will. And if it's not - how is
the length special?

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pps43
> Einstein found that the constant distance was the square root of x^2+y^2+z^2
> – ct^2, where c is the speed of light

Units don't match - ct^2 is in m*s, not m^2.

~~~
dagw
It's supposed to be (ct)^2

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panic
Is there an experiment which can test whether the Planck length really is the
shortest possible length?

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nabla9
There is no reason to expect that Planck length is the literally the shortest
possible length. I'm not aware of any theory that suggests that.

It's more accurate to talk about Planck scale and not think it as strict
limit.

Planck scale is where the structure of spacetime itself becomes dominated by
quantum effects and the structure of spacetime may start looking really
strange. Strange theories like loop quantum gravity, causal sets, causal
dynamical triangulation, fractal cosmology, etc. work at Planck scale.
According to fractal cosmology spacetime is 2-dimensional in Planck scale and
gradually becomes 4-dimensional in larger scales. Loop quantum gravity sees it
as "foamy".

Planck scale is also the area where measuring distances (differentiating with
different positions in space) becomes impossible.

~~~
TheOtherHobbes
I love these ideas, but they all assume that spacetime quanta, or nodes, or
whatever the hell they are, can still communicate and/or change state in some
way.

Which suggests internal structure of some kind.

I'm wary of any explanation that says "Well, it's just random", because
randomness turns out to be a complicated process.

It's hard to imagine that some kind of prototypical base quantum would be
inherently random _just because._

I suppose it's possible. But it would be unexpected.

