
The Mystery of Time’s Arrow - furcyd
http://nautil.us/issue/71/flow/the-mystery-of-times-arrow-rp
======
roberto
What if time's arrow can be reverted, and is being reverted all the time, but
we don't notice it because, just like and omelet would become an egg, our
brain state would revert to a previous one?

As far as we know time could be running in reverse, but the process in our
brains would make us feel like it flowing forward. The book "Permutation City"
explores this idea, albeit in simulated brains.

~~~
b_tterc_p
For all you know you don’t even experience time going forwards. At any given
instance, how do you know that you “experienced” the past second. What if your
conscious experience is just an instance at that point of existence? You can’t
point to recollection of the past second because that recollection happens
through time as well. What if that’s just an illusion of the brain state at
that time?

Did Descartes really think?

~~~
halgir
Also known as a Boltzmann Brain.

[https://en.wikipedia.org/wiki/Boltzmann_brain](https://en.wikipedia.org/wiki/Boltzmann_brain)

~~~
rexpop
I am very grateful to be introduced to this concept. During--and occasionally
since--a particularly traumatic psilocybin trip some years ago, I had the
distinct understanding that my consciousness had only just been put together
(or, rather, re-arranged from another, very alien form), memories and all. It
is comforting to have such bizarre experiences reflected in others' thought
experiments.

Classically, we understand our neurological arrangement to be a function of
each last instant's without discomfort. It's another thing entirely to
consider how we might have been arranged from wildly different previous
states.

Although there's no compelling evidence to support it, neither is there a way
to disprove it, I'm afraid.

~~~
AgentME
A really strange thing about Boltzmann brains is that if you suppose their
existence, then the question "Am I a Boltzmann brain?" becomes complicated. It
makes sense to ask "Is there a human thinking the thoughts I am thinking?" and
"Is there a Boltzmann brain thinking the thoughts I am thinking?", but if you
suppose the answer to both is yes, then when you ask the question "Which one
am I?", there's no pure logic you can follow within your mind to answer that
question, because both the human and the Boltzmann brain are in the same
mental state and any logic either of them follow will be followed by the
other, and any logic that comes up with a definite answer must be flawed
because it comes to a wrong answer for at least one of them.

Of course, it's not particularly useful to consider the Boltzmann brain
version of yourself because a Boltzmann brain's decisions don't have any
consequences. Time is better spent considering decisions by the consequences
of the human taking them. Maybe this implies that you should choose to define
"yourself" to refer to both your mental state combined with the ability to
make decisions of consequence, and then you can safely disregard the strange
kinship you may have with a Boltzmann brain. Though now this line of thought
invites interesting questions about how to define what makes a decision
consequential, and what exactly makes human decisions consequential...

------
femto
> You can make an egg into an omelet, but you can’t turn an omelet back into
> an egg.

The 2015 IgNobel was awarded for uncooking an egg!

[http://www.news.uwa.edu.au/201509258005/awards-and-
prizes/eg...](http://www.news.uwa.edu.au/201509258005/awards-and-prizes/egg-
research-cracks-top-prize)

~~~
saagarjha
> You can make an egg into an omelet, but you can’t turn an omelet back into
> an egg.

It's missing an asterisk:

* without expenditure of energy

~~~
baddox
You also can’t make an egg into an omelet without energy expenditure.

------
strainer
In a physical simulation, you can't simply set the timestep to -1 to recover
previous states for the sole reason that each step adds inaccuracy to the
model by way of rounding error.

Like this saying "There is nothing in the form of the laws of nature at the
fundamental microscopic level that distinguishes a direction of time." There
is nothing in the simulation which prefers to step time by 1 or -1 , but the
unavoidable rounding error means it can't step exactly backward. I guess its
intimately attached to the fact it cant step exactly forward.

This is why the shattered virtual object wont rearrange perfectly going
backwards - it didnt smash perfectly when it was going forward.

I had an idea for making previous states recoverable by applying extra
rounding between every timestep, but now I suspect this will not entirely work
either, as some least significant imprecision occuring during the timestep
will still occasionally trip the more significantly rounded 'interstep' state
values, irrecoverably.

~~~
incompatible
Perhaps the simulation isn't time reversible, but that doesn't say anything
about the reversibility of the laws of physics and the reversibility of the
universe. I.e., reversing the entire universe would still run the simulation
backwards, correctly, because it takes place at a lower level.

However, I think the point of the article is that given a deterministic
universe, even though it doesn't "run" forwards or backwards but just exists
throughout space-time, observers inside the universe can still observe an
"arrow of time" in the direction of more stability.

~~~
strainer
Im not sure. Simulated observers could also observe the direction of time
progression; that orders in the past become irrecoverable to them is a
mechanistic result of infinite precision not being preserved from one moment
to the next.

------
sctb
Does anyone know how this work relates to Rovelli's thermal time hypothesis?
([https://en.wikipedia.org/wiki/Thermal_time_hypothesis](https://en.wikipedia.org/wiki/Thermal_time_hypothesis))

~~~
platz
I thought Rovelli was into loop quantum gravity

------
femto
It strikes me as analogous to the near and far field of a radio antenna? The
complicated initial close-in chaos corresponds to the complicated near field
of an antenna. As the EM wave propagates further away from the antenna it
assumes a simpler "far field" structure. On other words, as the wave gets
further away from the antenna the physical extent of the antenna becomes
neligible compared to the distance propagated, so the field looks more and
more like that from a simpler point source.

------
Lerc
I always thought the mystery of why everything going the same way was a bit
odd considering our perspective.

It's like having a particle system create a million particles at x=0 with
random velocities then measuring a sample at 5000<x<5500 and wondering why
everything that goes through that range has a positive x velocity.

------
platz
e.g. you could have folks on the other end of the big bang, where the farther
you go back from our perspective, it looks like going into their future
instead of further into their past

~~~
hathawsh
That would be a fascinating idea for sci-fi! The inhabitants of two distant
worlds would be able to see each other's future but not their own.

------
galaxyLogic
I think it's no mystery at all if you consider Heisenberg's uncertainty
principle. To reverse the arrow of time would mean that all particles reversed
their momentum. Observing that maybe in a limited area of space would tell us
that the arrow of time has clearly been reversed since things move towards
more organization rather than less. The observed entropy would decrease.

But since particles do not even have precise momentum it makes no sense that
you could precisely reverse it. This imprecision is everywhere and as it
interacts with its surroundings it can only grow larger. Therefore entropy can
never decrease and time can never flow backwards.

~~~
tyscorp
Even if you could reverse the momentum of all particles, that wouldn't be
enough because T-symmetry can be violated.

------
brianberns
This is an interesting idea, and well presented.

I think the conventional explanation of the low entropy state of the early
universe is a brief period of “inflation” that resulted in an extremely smooth
and uniform density throughout the universe. Does the theory presented in this
article replace inflation?

------
amelius
Wow, what is happening to funding of academic research? Why do we need a
"Kickstarter" for scientific experiments?

[https://experiment.com/projects/are-we-catching-photons-
trav...](https://experiment.com/projects/are-we-catching-photons-traveling-in-
time)

~~~
halgir
Is appealing to distributed individual interest worse than appealing to
corporate interest?

