stupid physics questions

[pogo]

Conversely, if you say that a light year is always a relative measure, then the logic that declares that the observable universe extends further than the age of the universe doesn't make any sense, and the radius of the observable universe must then match the age of the observable universe.

I think this is the best way to think of it. We can see as far in distance only as far as the age of the universe. And we can see things which are so far away that we are seeing them when the universe was very young. But we think the universe is a lot bigger.

One problem is that although the laws of physics are expected to be the same throughout the universe those same laws suggest that our measures of distance and time are inherently local. Distance and time are defined by special relativity, which accurately describes flat spacetime. But space is not flat but curved; a little near masses like the Earth and Sun, a lot near Black Holes, and back on itself in the large-scale universe. The larger you go in the universe, or the further back in time you go, the more curved things get and the less usesful special relativity is; you need general relativity which allows for a changing measure of distance.

[gumboot]

What does "doesn't work" mean?

Is that to say that each observer would consider different points "half way", and, as you asked earlier, would measure the distance between the remote point and the relay as being less than the distance between the relay and itself?

[gumboot]

I think this is the best way to think of it. We can see as far in distance only as far as the age of the universe. And we can see things which are so far away that we are seeing them when the universe was very young. But we think the universe is a lot bigger.

A lot bigger than what? Wikipedia measures the observable universe as being larger than the age of the universe in "light years".

[gumboot]

I think my sticking point isn't anything more than the idea that Wikipedia appears to use inconsistent notions of a light year to define observability to extend further than the age in light years. It implies faster-than-light travel by using contemporary[1] light years to measure a distance which has been filled in subsequent to light travelling through it.


If we could control and reverse this expansion then I think we'd have Star-Trek-universe warp travel, wouldn't we?


[edit] [1] or possibly return-journey light years. I don't even know.

[Darkflame]

The core of this is whether spacetime is quantized or not isn't it?

The core of my question is this;

Is the idea of a continuous universe and finite information mutually exclusive?

I am perfectly happy to accept finite information if we live in a quantized universe.
The problem is, this does not seemed to be the consensus.
Yet finite information does seem to be the consensus.

Either I'm miss-reading the consensuses(?), or there seems to be something I am overlooking preventing position itself being a form of storing information (as apposed to state-changes of stuff).

[gumboot]

You can have discrete information with an apparently continuous expression. It's just that when you measure it and it looks like it's continuous, it's because you're measuring the wrong thing.

sin(kx) could be any value between -1 and 1, if you don't control x. That doesn't mean that sin(kx), or k, contain infinite information. You just need to control x to make the proper measurement of k.

[pogo]

Either I'm miss-reading the consensuses(?), or there seems to be something I am overlooking preventing position itself being a form of storing information (as apposed to state-changes of stuff).

Heisenberg’s uncertainty principle essentially prevents you measuring position to ever greater accuracy. It’s presented in other ways but the principle is about measuring, and explicitly places limits on how precise you can go.

https://en.wikipedia.org/wiki/Uncertainty_principle

More fundamentally everything at the quantum level is fuzzy. Particles do not exist, as they are often drawn, as little dots or balls with exact positions. They are more accurately described using probability distributions with no exact position. If you try and measure more and more precisely you would eventually get down to the quantum level and this fuzziness would defeat any quest to store infinite information.

[gumboot]

Your experiment doesn't work, because the rate of expansion of the universe is ... complicated to think about. It is (presumably) constant per unit distance, but the distance matters because at several billions of lightyears the expansion is faster than light, whereas between lightyears it definitely isn't anything like that fast, maybe as slow as the speed of sound or less.

Had another go at this... Wary of appeals to Zeno's paradox, there must be a distance that grows by a light year every year, and if you had that ahead of you on your journey you'd retreat faster than you'd advance (although your point of departure would also retreat faster, such that the percentage progress would always increase)... But if that distance were less than the radius of the observable universe then anything beyond it could never reach us, making it unobservable. If it was unobservable then it wouldn't be a part of the observable universe and they'd use a smaller figure.

Right?

So everything worth talking about is within that event horizon... Even if an implication there is that stuff is gradually dropping off the edge of it.

So... our universe really is shrinking. Crikey!


[edit] 140 million years to expand 1%, at present. So to retreat further than you advance, you must travel less than 1% of the total distance in 140 million years; so that distance must be about 14 billion light years. Which is about the age of the universe.

That's not a coincidence, is it. Is it? That's my stupid physics question for today. Is that a coincidence?

[Darkflame]

Either I'm miss-reading the consensuses(?), or there seems to be something I am overlooking preventing position itself being a form of storing information (as apposed to state-changes of stuff).

Heisenberg’s uncertainty principle essentially prevents you measuring position to ever greater accuracy. It’s presented in other ways but the principle is about measuring, and explicitly places limits on how precise you can go.

https://en.wikipedia.org/wiki/Uncertainty_principle

More fundamentally everything at the quantum level is fuzzy. Particles do not exist, as they are often drawn, as little dots or balls with exact positions. They are more accurately described using probability distributions with no exact position. If you try and measure more and more precisely you would eventually get down to the quantum level and this fuzziness would defeat any quest to store infinite information.

I was aware of that, but I am not sure it solves the (apparent paradox).

If we view atoms as fuzzy probability map, then we cant tell any of its parts positions true. But does not the map itself have a position? The "center" of the map?
Isn't it somewhat like this;



If that X axis is continuous then the probability maps center can still be anywhere along it, which still seems to fit my analogy of a "point on a line" being able to contain infinite information. In this case the "point" is, I dunno, the "most likely" position. Or at least the average over some small timescale.


Now to be clear; I am very much talking only in hypothetical here. Not saying we could ever store/extract information this way - merely what the universe itself ""stores""

[pogo]

There you run up against one of the most paradoxical aspects of QM. When you describe a particle as having a probability distribution that is not like e.g. the probability distribution of a population, where you can take samples, find the average and spread. It’s a single particle. If you try and measure it you get one value. That could be in the centre or anywhere else, with the chance of each value being given by the probability distribution.

So there is no way to discover the underlying probability distribution. You can sample it, but as you can only take one sample that tells you nothing. Taking that sample, making the measurement, removes the uncertainty so you no longer have a probability distribution. You just have one imprecise measurement. Sampling multiple particles is no good as each is has its own properties.

[Orava]

US town rejects solar panels amid fears they 'suck up all the energy from the sun'.

Well they do, in a way, don't they? As for causing cancer...

[Absolute_Zero]

The Standard Model could be in difficulty... CMS and ATLAS at CERN are reporting a diphoton excess at ~750GeV with a combined sigma currently at ~4.5 - looks like a new boson has introduced itself.

[Dio]

diphoton channel only, EM interaction and nothing else?

(edit) found this on it.

[Absolute_Zero]

Falkowski has a good rep in the hep-ph blog market. Seems a balanced summary.

Personally, I hope this turns out to be the calling-card of the Next-to-Minimal Supersymmetric Standard Model.

Whatever, if physical, then the super-super collider proposed by China is sure to become a thing.

[Dio]

Lubos Motl called that one out. Yes, there will be a lot of collider-builders looking cheerful.