
Rebuilding Quantum Theory From Simple Physical Principles - behoove
https://www.quantamagazine.org/quantum-theory-rebuilt-from-simple-physical-principles-20170830
======
bigtimber
Fyi, the topic was discussed a few months back in
[https://news.ycombinator.com/item?id=15163528](https://news.ycombinator.com/item?id=15163528)
after the _Quantamagazine_ article was reprinted in _Wired_.

------
platz
> Wins

Neutrinos aren't massless

Confirmed higgs

> Problems

Hierarchy problem

Fine tuning

Why is the cosmological constant so "wrong compared to theory"

No evidence for supersymmetry yet at 10^-17cm via LHC

No evidence for WIMPs

How do we combine QM + GR?

Do black holes destroy information? How to solve the BH firewall problem?

> Speculation

Is there supersymmetry at higher energies than the LHC can probe?

Is spacetime doomed? I.e. is space-time a hologram on the boundary or some
other emergent phenomenon

Is there a multiverse?

Is decoherence a solution, or does the wave function "collapse", or simply
many-worlds?

Is perturbation theory sensible or is there a deeper more elegant way to
calculate scattering?

Is time emergent or fundamental?

------
wruza
After familiarizing with QM/SR concepts some years ago, I came to the
conclusion that there is nothing more strange and pointless than the world
without these two. If max speed was infinite (or finite but non-relative,
which is essentially the same) and there was no probabilistic outcomes, then
the world would "happen to the end" instantly and/or with analytically
predefined series of events. From any initial state. The entire "consequence"
concept would fall apart. There is no point for the universe to exist in
classical & atomic-ball electron mode.

Idk why both seem so unnatural to so many people who try to get what it means;
it feels like it should be obvious instead - it means evolving existence, the
only thing you're able to appear in and think about it. Classical uniform
fundamental time is much stranger to me than what emerges from what we have
now; we simply shifted our focus to "oh" forgetting how much "wtf" was left
behind.

I'm not claiming any deep-enough physics or math knowledge (layman actually),
consider it a funny philosophical view.

~~~
chr1
> with analytically predefined series of events.

This doesn't make universe less interesting or more predictable. Consider
Mandelbrots set, it is fully analytically predefined, but only way to find
it's details is to perform the whole calculation.

Similarly the universe can be predefined, but the only way of finding its
state after some amount of time can be performing a calculation fully
equivalent to letting the universe to live for that time.

~~~
wruza
>amount of time can be performing a calculation fully equivalent to letting
the universe to live for that time

This one is very interesting since it brings back the question what time
really is. Your point involves “metacircular” observer that can only
work/simulate as fast as it can, but the definition of “fast” is external to
it. Sure, if we simulate predefined-but-calc-required in _our_ universe, then
it will take time. But why should we measure it this way? I mean, does
calculation _process_ exist at all without something that requires time for
it?

[Or we’re really talking about the same fundamental thing that lies behind
both our and hypothetically deterministic universe.]

~~~
chr1
Say it is possible to calculate future of a sufficiently complex physical
system like a person on a Turing machine by knowing the current state of the
system.

Then, according to this idea, the calculation can not be simplified by using
some kind of formula that predicts the final state, and one needs to fully
compute all the intermediate states, which means your computation is fully
equivalent to that person living for the time for which you want to calculate
the final state.

So time here is the internal time for the system of your calculation, and not
related to the time you take to calculate. This internal time is nothing more
than a counter you use, and You can actually stop your calculation, change
something in the initial state and calculate again.

I find this fascinating because it kind of explains the universe being
predictable, and people having free will: everything is predefined, but only
way to know what the choice of complex system will be is letting that system
to make the choice!

If the view that consciousness can be explained without requiring quantum
physics is correct, then this is true independently of specifics of
simulated/real universe, and is just the way information/computation works.

But then maybe Penrose is right, and consciousness can't be calculated on a
Turing machine, and we still have lots of interesting science to discover.

------
dboreham
Reading this I see for the first time why the notion that the universe is a
simulation isn't so far fetched.

~~~
danbruc
I have to disagree and I can not really understand what is so appealing about
the simulation idea to many. It is an idea that will lead nowhere because you
are unable to distinguish a real universe from a simulated one. In order to do
this you would have to know what at least one of those scenarios looks like
and then compare the universe you observe to what you know to be true about a
real or simulated universe.

It is common to base such thoughts on analogies between our universe and our
computers, i.e. our computers have only finite precision while the universe
seems continuous, at least to a very good approximation. Therefore if we would
detect rounding errors in the universe we would know that the universe is
actually a simulation.

But that is at least naive and most likely not true. How would you know that a
real universe does not have finite precision? Why would you assume simulation
must have finite precision? And you have to answer the same question for any
other feature you want to use to make the distinction.

~~~
indubitable
Personally I find the peculiar implication of a simple question so appealing.
_Will we eventually be able to create simulations that one would be unable to
differentiate from reality if that simulation is all they had ever known?_ The
answer there is quite self evident, yet it simultaneously somehow implies it
is highly likely that we are ourselves within a simulation.

The reason is that we can safely assume that we are within one of _n + 1_
realities. The _n_ simulated realities and the _1_ real reality. Unless you
attribute some sort of exceptionalism bordering on creationism to our
existence, there's every reason to think that _n_ is going to proportional to
the number of advanced civilizations in existence and is presumably going to
be very very large. And as you increase _n_ the odds of us actually being in
the 'real' reality, which are of course just 1/(n+1), approach 0.

Like you mention it's something that doesn't necessarily go anywhere. Even if
you "prove" it after death, that life you'd be experiencing at that point
faces the same logical issue - at least unless the argument loses consistency
at some point. Something most seem reluctant to admit is that it's also
comforting as an atheist. I always expected the infinity of time after my
existence to be very much akin to the infinity of time before my existence.
That's just disappointing. The seemingly high probability that all is not as
it seems is certainly emotionally appealing. But it's certainly not just the
emotional appeal driving me there - I could obviously have chosen to invoke
Pascal's Wager in the decades of time prior to considering this, but it seemed
fake -- this, somehow, does not.

It also answers, or at least compellingly kicks the can, of the question of
existence. If I write a program to spit out a random number, I presume that
there is no entity that suddenly whisks into existence under the false
impression that it is choosing a random number - which it then decides upon,
before then being whisked out of existence. So why am _I_ , the 'thing'
spectating the outcome of the series of chemical and electrical reactions
carried out by this body, here? Descartes would have quite the time if the
answer to our little question had been yes during his time. It changes the
picture so much more than the dreams that drove his ponderances.

\---

From a scientific point of view, it's obviously not a great concept as it
cannot be falsified. And like you mention, it also cannot really be physically
proven without begging the question. On the other hand, it can be treated as a
soft science and if a preponderance of evidence does lean towards supporting
it then we can at least say, _" Hmm.. well we can't really say anything for
certain, but that's certainly interesting."_

~~~
SomeStupidPoint
Could you support the premise you can make an undetectable simulation?

That's a key proposition and you don't support it at all. I find the idea
highly questionable.

~~~
danbruc
Do you think a NPC in a game could figure out that he is just a character
controlled by the game logic? Current games are obviously far away from having
conscious NPCs but I neither see any fundamental problem with having NPCs
controlled by artificial brains nor any obvious way how such a NPC could
figure out that he lives within a game.

Or what if, while you are asleep, someone essentially detaches your brain from
your body and uses the signals your brain sends to control a simulation of
your body in a virtual environment and feeds back the simulation output into
your brain as what you see, hear, feel, and smell? How would you detect that
you are no longer really in the real world when you wake up?

~~~
SomeStupidPoint
Yes, lots of ways:

For example, in Minecraft you can build a redstone interferometer to detect
things about the computer you're executing on and over time the statistical
behavior will detect the physics of the real system.

A character in Minecraft could build a cosmic ray detector, for instance.

So yes, absolutely -- my expectation is that any intelligent structure in a
computational "bubble" will be able to detect that it's in a bubble managed by
some outside system.

Is your argument entirely from lack of imagination in how it could be done?

~~~
danbruc
Is a redstone interferometer an actually thing, a quick search didn't turn
anything up? But even if you could detect influences from the outer reality
within the game world, how would you decide between them being part of the
game mechanics and them being shadows of the outer world given that you have
no ground truth knowledge of what the game is supposed to be like?

~~~
SomeStupidPoint
> Is a redstone interferometer an actually thing, a quick search didn't turn
> anything up?

I'm probably using slightly different terminology than other people -- I
haven't played much in a while.

The basic idea is to use two quasi-connected redstone wires hooked up to a
piston -- one providing an update signal but no power and one providing power
but no update signal.

The circuit is such that the two wires are actually branches off of a single
redstone wire, using only redstone -- so you can detect if the left or right
branch off of a redstone line updates first (within a single update cycle)
based on if the piston extends: it only extends if the line carrying the
update signal is updated after the line carrying the power signal. (If they
come in the other order, it stays retracted because it updates before there's
power available.)

> how would you decide between them being part of the game mechanics and them
> being shadows of the outer world given that you have no ground truth
> knowledge of what the game is supposed to be like?

You only have an operational model, just like us -- but it's eventually going
to look like an extremely localized computation running their world that
occasionally gets bumped by outside sources. That sounds like them discovering
that their reality is a subregion hosted in another, richer reality.

The question of "game mechanics" only has meaning to the people outside in
their language for discussing their actions -- at the end of the day, there is
no "game", there's only what the simulation does as a facet of reality. The
people inside will accurately suss out a model that includes a structure that
looks like them being run as a simulation.

How they interpret that is likely to be different, but no more or less
correct, than how we do.

------
amelius
Any role for Pilot Wave Theory here?

[https://www.quantamagazine.org/pilot-wave-theory-gains-
exper...](https://www.quantamagazine.org/pilot-wave-theory-gains-experimental-
support-20160516/)

> An experiment claims to have invalidated a decades-old criticism against
> pilot-wave theory, an alternative formulation of quantum mechanics that
> avoids the most baffling features of the subatomic universe.

