

The Bridge From Nowhere - dnetesn
http://nautil.us/issue/16/nothingness/the-bridge-from-nowhere

======
Xcelerate
I've found that, at least for me personally, quantum mechanics is much less
strange when you ignore the sensationalistic, new-age mysticism quips and
focuses on the actual math itself. Let me give some examples:

"A particle travels through all possible paths at once and only chooses one
when you look at it".

No, a particle's wavefunction is a vector in an abstract Hilbert space that
_can be_ expressed as a linear combination of basis state vectors (|Ψ> = Σ
α_i|Φ_i>), and it collapses (decohers) upon measurement to one of them with
probability |α_i|^2 when those basis vectors correspond to the observable's
eigenstates.

Or, if that's too complicated: a wavefunction of a particle is just a function
that can be represented as the weighted sum of other functions, each
representing a different path that the particle can traverse. When you measure
the particle, the result corresponds to only one of those functions.

Perhaps the first explanation requires you to Google a little bit or pick up a
math textbook if you're not familiar with some of the terms, and perhaps the
second explanation isn't quite accurate enough, but goodness, they both make a
heck of a lot more sense to me than some kind of magical "everything at once"
phrase!

Another phrase, this one from the article: "The rules of quantum mechanics
allow — actually, require — energy (and, by E=mc2, mass) to appear 'out of
nowhere,' from nothing."

No they don't. HΨ = EΨ is the time-independent Schrödinger equation. E is a
constant -- a real number. It doesn't change. Furthermore, the article goes on
to mention the energy-time uncertainty principle, and a lot of other articles
mention that energy can be "borrowed" to create virtual particles out of
nothing. This also isn't true, for two reasons. Firstly, there is no energy-
time uncertainty principle, because time isn't an operator. You _can_ derive a
relationship between the two, but it's not the same kind as the Heisenberg
uncertainty principle. And secondly, virtual particles are a mathematical
artifact of a technique called perturbation theory (a technique used in many
fields, not just QM). Perturbation theory is just one means of solving an
equation, and if you try to solve the equation with a different technique, you
have no need for virtual particles.

I'm really glad that so many articles on quantum physics are "popping into
existence". It's a cool subject. But I'm worried that these inaccurate little
catchphrases I hear all the time are causing more headaches, confusion, and
sensationalism than quantum mechanics already causes by itself alone.

(There are articles written by actual physicists and quantum information
scientists that clarify physics concepts to non-scientists in an easily
understandable, yet _also accurate_ way. Scott Aaronson and Matt Strassler are
two that come to mind.)

------
idlewords
This essay is pretty painful. For a much more enjoyable take on the question,
I highly recommend Holt's book
[https://cmdev.com/isbn/0871403595](https://cmdev.com/isbn/0871403595). He
talks to a number of philosophers and physicists whose opinions cover the
spectrum from "the question is not worth asking" to "God is the answer", with
a lot of interesting ground in between. [edit: fixed misremembered book]

~~~
cratermoon
I'd also recommend "Why Does the World Exist?: An Existential Detective
Story", by Jim Holt.
[https://cmdev.com/isbn/0871403595](https://cmdev.com/isbn/0871403595)

~~~
idlewords
That's actually the book I had in mind-thank you! My memory flaked on me.

------
spenrose
I highly recommend Krauss' book A Universe From Nothing on this topic.

------
lotsofmangos
The prime mover has been an issue for quite a while. I particularly like one
of the earliest suggestions, namely _that which moves itself is immortal_ ,
though as an answer it creates more problems than it solves.

