The Quantum Mechanics of Fate (2014)
nautil.us
nautil.us
This is flat-out not true. The standard interpretation is that the entangled objects are part of a single quantum state. Measurement/observation of the state collapses the wave-function, and does not necessarily imply communication between the constituent parts.
Unrelated Query: How can something be "flat out not true" if it's only an interpretation? Seems to be that what you're describing is a consensus or popular view opposed to a hard fact or universal truth.
I think that chakademus meant that it is flat-out not true that "the standard interpretation … is that there is some kind of instant communication happening between the two particles" (notice the scope of the quotation marks); that is, that this is not the standard interpretation, not that this interpretation is 'wrong' (whatever that means).
What role does relativity play in this discussion?
From the point of view of a photon, there is no lapse in time between emission and absorption. Emission and absorption happens instantaneously, since time never "ticks" for the photon as it traverses space. So, at least from the photon's point of view, there is no need to evoke the past/future causality in this situation.
This is highly misleading. The arrow of time is not thermodynamic, it's quantum. It's defined by increased entanglement, not increased entropy.
http://blog.rongarret.info/2014/10/parallel-universes-and-ar...
That's not at all what I remember from physics class when I was at university, and would seem to imply (incorrectly) that non-QM models can't produce an arrow of time.
Used a 2-mbit source of randomness, been running the setup continuously to get a few terabits of data. Fixed a bunch of imbalances in the state-of-the-art commercially available source of physical randomness. Nope. Source code/results are available here: https://code.google.com/p/reasonable-deviations/source/brows...
I know it's been recently trendy for armchair physicists to post grand philosophical claims about the universe from some vague understandings of Bell's Inequality and/or entanglement, and blurring the line between philosophy of physics with physics. But your casual dismissal of entropic thermodynamic arrow-of-time time in favor of purely increasing entanglement ranks way high on the BS meter.
For context - I have a PhD in experimental condensed-matter physics, and TA'd thermodynamics and statistical mechanics for several years. I left the field of physics many years ago so maybe there were some notable recent developments in quantum information theory that I missed. But I skimmed your linked article and can't take it seriously. Would love a better source of you can provide one, eg peer-reviewed (in a respectable physics journal) or written by an actual career physicist at a reputable institution.
This doesn't discuss the arrow-of-time directly, but it's a pretty straightforward corollary.
I'd still maintain the original comment in the original article is correct, that the arrow of time is still driven by 'thermodynamic' processes, where I'm allowing thermodynamic really means statistical mechanical process, and statistical mechanics includes (as it always has) quantum statistics of quantum processes.
Ie, your arxiv link gives further quantum detail of the underlying macroscopic measurements (eg, the schrodinger cat example).
But the irreversibility and arrow-of-time come from the enanglement of the particle with the 10^23 atoms of the macroscopic observer system. And in that sense the irreversibility is more due to the large size of the system, just like a classical example (such as shaking a bottle of originally separated black/white marbles) than the fact that there is quantum entanglement between the particle and the measurement system.
So while Cerf and Adami identified interesting quantum processes to describe underlying interactions, the irreversibility still comes from a statistical consideration of the interaction with a macroscopically large system. Just like the traditional arrow-of-time statement that you had originally refuted.
>This irreversibility is completely equivalent to the irreversibility in classical mechanics. Indeed, classically, to reverse the microscopic time evolution, it is necessary to invert the velocity of all the particles, the practical impossibility of which gives a macroscopic irreversible aspect to time evolution. In quantum mechanics, it is necessary to undo any unitary evolution associated with all interactions that particles have undergone, so that reversibility is practically impossible if a macroscopic number of particles have been involved. We are led to conclude that irreversibility is not an inherent feature of quantum mechanics.
I had to call you on this. Bold claims require strong confirmation. And even the arxiv paper you linked to makes the same statement that I defended - that irreversibility of purely quantum processes is still due to the macroscopic (ie large) system size, which immediately implies the same broad thermodynamic (and statistical ensemble) considerations we've been assuming for the past century.
Also, this is HN comments, not Physics Review A. Not everything that gets said here needs to pass the highest standards of peer review.
The QM explanation is not contrary; it's just a special case of the thermodynamic explanation; entanglement is one way entropy can increase, but it happens in the classical world too, which also has time symmetric laws.
So in what sense is someone erring when they call it a thermodynamic arrow of time?
edit: clarity.
Imagine that you are in Stalinist Russia and win a minor scientific prize for a paper you wrote. There is a purge, and while you manage to not get deported to Siberia, the prize is reassigned to a less brilliant but more politically orthodox colleague, to the point that he is listed as first author of your paper.
He goes on to have a better career because of this paper, and by the end of the affair, nobody remembers that you wrote the paper to begin with.
If all observable effects of an events have been retconned, can that event be said to have occured?
Can a similar situation happen in physics, and if so, does it "count" if only macroscopic effects are reversed? (To keep with the analogy, in this case, everything but your memory has been changed, but your memory hasn't been - although it might over time, due to you wanting to avoid cognitive dissonance).
Using the above analogy the message sent from the future (the man exists) to the past will prevent the grandfather to be killed just like the decaying atom, maybe the messages send back and forth from the future rewrites the events to prevent the paradox, something like backtracking until it works.
Imagine you have a billiard table, on which there's a wormhole. If you roll a billiard ball into the wormhole on the right trajectory, it will emerge three seconds prior to entering the wormhole, hit its earlier self a solid blow, and its earlier self will never enter the wormhole, creating a paradox.
But when you try, it emerges from the wormhole on an altered trajectory, and strikes itself only a glancing blow. And why did it emerge with an altered trajectory? Because it was struck a glancing blow.
This is the Novikov self-consistency principle [1]. Physicists have been unable to find initial conditions that don't allow a consistent solution. On the other hand, nobody has proven that consistent solutions always exist. And sometimes there are lots of consistent solutions. (I wonder whether that's why quantum physics isn't deterministic, but I'm no physicist.)
[1] http://en.wikipedia.org/wiki/Novikov_self-consistency_princi...
I have to admit I don't know what that means. Anyone got a way to describe this?
https://en.wikipedia.org/wiki/Buckling
In short:
If a structure fails by buckling only depends on the following properties:
load on the structure, modulus of elasticity, moment of inertia, length of the structure and a factor, whose value depends on the conditions of end support of the structure.
The factor is a number between 0.5 and 2 depending only on the condition of both ends. For example if both ends are free to rotate it is 1.0, if both are fixed, it is 0.50, and so on.
If the past is malleable, we could keep using the scientific method, but with humility, like: "The experiment's data support my claim so long as there was not unknown interference from actors unbound by linear time, space, and matter."
That sentiment is not too far from the attitude of many of us, rational people, who believe that in addition to humanly measurable causes, there are also supernatural or spiritual realities to consider.
If some causal effects might be travelling back in time, we should investigate it instead of just saying, "I don't like it, so let's just define it the way we want."