A Universe Made of Tiny, Random Chunks (2013)

http://nautil.us/issue/2/uncertainty/a-universe-made-of-tiny-random-chunks

by dnetesn • 10 years ago

55 40 10 years ago

panic• 10 years ago

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

maggit• 10 years ago

As I understand it, this is indeed a fundamental feature of the Planck length; The universe might have structure smaller than this, but we wouldn't be able to tell. So the Planck length is the shortest meaningful length, in that we would never be able to discern structure smaller than this.

criddell3• 10 years ago

So, doesn't that suggest there's a Planck length for time? So the distance between two points in space-time is sqrt(x^2 + y^2 + z^2 - ct). If you try to find the distance of a point in space at two different times, does the Plank length dictate some type of Plank interval?

nabla9• 10 years ago

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• 10 years ago

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.

xioxox• 10 years ago

The operating energy of the LHC is around 15 orders of magnitude less than the Planck energy (if I worked it out correctly). Therefore we cannot directly probe Planck length scales.

dogma11385• 10 years ago

Planck length, nor any other Planck unit isn't the "shortest/smallest" anything* at least it was never intended to be that.

These units are very useful in QM and as "constants" (not the best choice of words since Planck units intentionally ignore constant values to some extent) that can be used to describe a relativistic universe.

*You can use Planck Length/Time to put a lower limit on any possible wavelength that below it a wave cannot exist, other Planck units can also be in the ballpark of the smallest possible unit/quanta of various things in various theories.

gizmo686• 10 years ago

Not really.

The uncertainty principle states that the product of the standard deviation of the momentum and posisition of a particle is bounded from below by h/4pi, where h is the plank constant.

This means that, in order to probe small distances, we must have great uncertainty in the momentum invovled, which means that there must be a lot of kinetic energy in the system. As the distances we probe become smaller, we have an increasing amount of energy in a decreasing amount of space.

E=mc^2 tells us that energy and mass are interchangeable. Specifically, energy, like mass, causes gravity. In order to probe below the plank length, we would need to put so much gravity in so small a space that we would form a black hole. However, because we cannot observe the inside of a blackhole, this prevents us from observing anything smaller than the plank length.

ajuc2• 10 years ago

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?

chriswarbo• 10 years ago

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 :)

ajuc2• 10 years ago

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?

haversine02• 10 years ago

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.

kowdermeister• 10 years ago

I see some hints too, but that's probably because my mind is wired to be programmer :) So it's probably just a sort of confirmation bias.

However seeing the quantum effects like a version of compression, dark matter and dark energy which could be an ugly hack to stabilize matter and galaxies, the fractal self similarity of the universe is just too amusing to ignore :)

Razengan• 10 years ago

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. :)

dogma11385• 10 years ago

QM can be defined by the fact that the reality you observe isn't the "actual reality", but overall it doesn't really matter.

Wave-particle duality is a bit of a misnomer it's more of a pop-sci concept, all particles are defined by their wave function and there isn't a "particle function".

And if you think that we are too biased towards picturing everything made out of discrete parts then you won't like QM which is basically what the Q stands for which is "quanta" as in the smallest clump-thing-w/e of something.

That said most people that choose to study physics in high school (year 10-12) and or college would be exposed to Quantum Field Theory which makes everything make considerably more sense when you start thinking about everything in terms of fields.

Once you no longer think of an electron as an individual thing but as a electron field that extends through all space and the particles are the quanta of that field as in localized excitations of the field which when they reach a certain amplitude or energy level bring forth something we can measure and identify as an electron.

I wish QFT would be popularized more because it would bring so many important concepts into the common sense realm and it would actually be easier to explain things like why do particle accelerators work.

m12k• 10 years ago

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... ). 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... ). 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.

eli_gottlieb• 10 years ago

I think that gets it backwards: the universe can move information around and perform computation because it has a level where things become both discrete and stochastic.

platz• 10 years ago

I'm not sure the existence of the planck length implies a lattice; see raattgift's comment https://news.ycombinator.com/item?id=12382308

_0ffh• 10 years ago

FWIW, my own intuition it precisely the opposite. I would be very surprised if reality turned out to be continuous, because of the resulting infinite information density.

jonsen• 10 years ago

That would also account for all the bugs.

jamesdsadler• 10 years ago

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.

vog2• 10 years ago

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.

dogma11385• 10 years ago

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.

Zigurd• 10 years ago

A bit of a quibble but Lorentz transforms are a consequence of Special Relatively, and therefore predate General Relativity. That is, the objection you are raising would apply to frames of reference without referring to General Relativity, just Special relativity.

aperrien• 10 years ago

Is that testable in some way? Say by putting a set of devices that would measure h and G on a spaceship or satellite?

dopu• 10 years ago

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.

pps43• 10 years ago

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• 10 years ago

It's supposed to be (ct)^2

amai• 10 years ago

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.

A Universe Made of Tiny, Random Chunks (2013)

Related Stories