
To John Archibald Wheeler, the race to explain time was personal - dnetesn
http://nautil.us/issue/9/time/haunted-by-his-brother-he-revolutionized-physics
======
joaorico
Freeman Dyson, another important physicist, wrote this a few years ago:

"I changed my mind about an important historical question: did the nuclear
bombings of Hiroshima and Nagasaki bring World War Two to an end? Until this
year I used to say, perhaps. Now, because of new facts, I say no. This
question is important, because the myth of the nuclear bombs bringing the war
to an end is widely believed. To demolish this myth may be a useful first step
toward ridding the world of nuclear weapons."

Here's the rest of the text: [http://www.edge.org/response-
detail/11732](http://www.edge.org/response-detail/11732)

~~~
tzs
Wheeler was worried about the war in Europe, though, and what could have been
had the bombs been developed a year earlier. That would have put them early
enough to consider delaying D-Day until after the bombs were available.

What, I wonder, would have turned out different if D-Day had started with
nuking Berchtesgaden?

------
AnimalMuppet
I think this is a misunderstanding of what's going on in quantum mechanics. A
photon is emitted as a probability wave function. (Note well: This is _not_
the same as "sometimes a photon acts like a wave!) It travels as a probability
wave function. It gets to the detector as a probability wave function. The
form of the detector determines how the wave function collapses into an
observable state. _That 's_ when the "choice" gets made. There is no
projection of the choice onto the past; there is only the projection of the
choice onto the probability wave function in the present. So this
"retrocausality" stuff is actually a fundamental mis-understanding of quantum
mechanics.

What the article got right: Relativity and quantum mechanics are talking about
two fundamentally different things when they use the word "time". Reconciling
those two ideas is going to be critical to a fundamental understanding of the
universe.

~~~
physonaught
That is true, but, (if you haven't already), I would recommend looking into
the delayed choice quantum eraser experiment. I think it is probably more true
to the essences of what the article was trying to communicate.

I don't think I can do the idea justice, but the basic idea is such: if you
'tag' the photons in the double-slit experiment by which path they went
through, then you necessarily break superposition and won't see an
interference pattern.

However, if you 'throw' away this information completely, the interference
pattern re-emerges. The delayed-choice part of it is just a way to through
away the 'tag' information after the photon has moved through the slits. It
seems to suggest that you can uncollapse a wavefunction if you just erase any
knowledge you have of the measurement you made. (I've probably butchered it,
read here for more[1])

Although, honestly, you don't need retrocausality, and personally I think it
has much more interesting applications to information theory (how does one
destroy information? How does the wavefunction know about our records? What
even is information, man? etc)

[1]
[http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser](http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser)

~~~
georgemcbay
Related, worth watching (IMO):

[http://youtu.be/dEaecUuEqfc](http://youtu.be/dEaecUuEqfc)

------
elpachuco
>>In 1984, Alley—along with Oleg Jakubowicz and William Wickes, both of whom
had also been in the audience that day—finally got the experiment to run. It
worked just as Wheeler had imagined: measurements made in the present can
create the past.

I'm not a physicist so unfortunately I don't know whether this is true.
However, of all the documentaries on Physics that I've seen they have never
mentioned this.

Could anybody please chime in whether this is true.

~~~
Ono-Sendai
I can't tell you if it's true or not, but you can read more about it here:
[http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experi...](http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment)

~~~
ctchocula
Here's a Wheeler quote from the link: 'Actually, quantum phenomena are neither
waves nor particles but are intrinsically undefined until the moment they are
measured. In a sense, the British philosopher Bishop Berkeley was right when
he asserted two centuries ago "to be is to be perceived."'

Could this be used as an argument that we are inside the simulation of the
universe? I mean if I were to design a game, I might leave the state undefined
until it's necessary for it to be known (by some consciousness perhaps).

~~~
Ono-Sendai
The state is not really 'undefined'. Rather there is a well defined
wavefunction (that is governed by precise evolution rules) that 'collapses' to
a single point when a position measurement is taken. That's the Copenhagen
interpretation at least :)

~~~
ctchocula
Yet there is something "undefined" about the phenomenon we're seeing. In the
context of the quote, what is undefined is whether the the quantum phenomena
is a wave or a particle. I found a name for the concept I was describing:
[https://en.wikipedia.org/wiki/Digital_physics](https://en.wikipedia.org/wiki/Digital_physics)

------
jsun
Unsourced wikipedia articles seem to suggest that Wheeler believed the exact
opposite on retrocausality. Since both pieces seem to cite no academic sources
I will leave it to you to determine which is true.

[http://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_expe...](http://en.wikipedia.org/wiki/Wheeler%27s_delayed_choice_experiment#Cosmic_interferometer)

