Einstein for Everyone

http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/index.html

by urbannomad • 15 years ago

216 18 15 years ago

meow• 15 years ago

I was looking for something like this for ever.

aik• 15 years ago

From the "Completeness of Quantum Theory" chapter (on one theory of the determinability of quantum systems): "If an atom has a probability of one half of radioactive decay over an hour, then all that really means is that its wave function describes an ensemble of many different atomic systems, half of which decay in an hour. Whether one particular atom in the ensemble will decay in one hour is definitely determinable. However we will not be able to discern it if all we know is the quantum wave associated with it. Whether it decays or not depends upon properties of that system that have been smoothed away by the quantum wave and thus are unknown to us. It is our ignorance of these smoothed away properties that makes a probabilistic assertion the best we can do."

HN, what does "Whether it decays or not depends upon properties of that system that have been smoothed away by the quantum wave" mean?! What properties exactly, and smoothed away how? Just by the fact that observing the system causes a change within the system and therefore changes the quantum waves?

blatherard• 15 years ago

As I understand it, Einstein was arguing that quantum theory was basically incomplete. That it provided a statistical view of unknown, underlying deterministic processes.

To say that properties "have been smoothed away" means that the particular statistical measures that quantum theory was using were losing the fine-grained detail necessary for understanding particular events. It's not that the "quantum wave" is literally smoothing things in the world, but that the theory of the "quantum wave" is disregarding particular facts.

Imagine that we described human populations without having the ability to observe individual sex characteristics, or individual human interactions. We might say things like "a human has a 10% chance of splitting into two humans over the course of a 20 year span." In this case, our statistics "smooth away" differences such as sex, and the interactions of specific humans over time, leaving us with a probabilistic statement. We might start reading the apparent non-determinism as a fact of nature, rather than as a problem with our knowledge.

mechanical_fish• 15 years ago

I was quite confused by this statement, because it just looks wrong. Upon consulting the text you are citing, I figured out why: This is the author's summary of Einstein's position on the determinability of quantum systems, and Einstein was wrong, famously wrong. This statement is about how Einstein thought the world worked, not about how the world actually works.

This statement you quote has often been called by the jargon name "hidden variables theory". You're asking: What are these hidden variables? Well, Einstein could never find them, and later work has shown that this is because they don't exist. Read the end of the chapter first. ;)

Incidentally, at first glance this chapter doesn't look like light reading.

othermaciej• 15 years ago

Technically, the only thing that is known not to exist is local hidden variables. There are non-local hidden variable theories which are consistent with all known experiments. Unfortunately, they are also not distinguishable by experiment from more mainstream interpretations of QM.

Here is an example of a non-local hidden variable theory: http://en.wikipedia.org/wiki/Bohm_interpretation

amalcon• 15 years ago

Einstein's view was more or less that there is some state contained in each particle that determines its quantum effects. We do not, however, have access to that state, so we instead do all work with statistical approximations of that state. The statistical approximations encompass all unknown information, and thus "smooth it over".

He put forth this theory before the EPR experiments (he's the E); these experiments made that interpretation unlikely. Specifically, the EPR experiments showed that the state (if any) is probably non-local.

SandB0x• 15 years ago

My favourite book on special relativity is Spacetime Physics by Taylor and Wheeler. It's intuitive, clearly written and well laid out, with an Edward Tufte style column of text running along the main body that stops you getting lost in the equations.

Some parts of the first edition are available online: http://www.eftaylor.com/special.html http://www.eftaylor.com/pub/spacetime/STP1stEdThruP20.pdf

autalpha• 15 years ago

Bookmarked... will read later. Thank you for a great find :)

tel2• 15 years ago

While this looks like a very fascinating book/course, does anyone have a recommendation for learning general relativity rapidly in a way that abuses mathematical knowledge? I want to brush up on tensor math and variational calculus and use it as a motivating core topic.

I'm looking for the tersest complete guide from Newtonian physics to GR. Single author would be best, but I imagine it's not possible.

tel2• 15 years ago

Reddit's r/AskScience recommended MTW's Gravitation[1], Wald's General Relativity[2], and, to begin, Sean Carroll's GR lecture notes[3].

Shameless affiliate links:

[1] http://www.amazon.com/gp/product/0716703440/ref=as_li_qf_sp_...

[2] http://rcm.amazon.com/e/cm?t=sdbo07-20&o=1&p=8&l...

[3] http://preposterousuniverse.com/grnotes/

bermanoid• 15 years ago

I second these recs: all three are fantastic sources. MTW is very imposing (the damn thing must weigh twenty pounds), but don't be threatened, it is a crystal clear exposition that you really should not miss.

I'm not quite sure, though, if tel was asking for full mathematical developments of the theory (in which case the combo of MTW and Wald are, IMO, indisputable must haves), or something that just gets to the point quickly, assuming that you don't need help on the math.

In any case, anyone and everyone should also read Penrose's Road To Reality (my own shameless affiliate link: http://amzn.com/0679776311?tag=gubbins-20) for a very different take on...well, pretty much everything. The book is a complete failure at its stated goal of making mathematical physics accessible for a lay audience (I suspect when you're as smart as Penrose it's hard to figure out what an average Joe is capable of grokking...), but as a casual and wildly different sweep through a lot of interesting topics for someone that already knows math, it's fantastic.

8worm• 15 years ago

Bookmarked! I loved it.

elptacek• 15 years ago

If you like this, you will also like this:

http://www.amazon.com/Quantum-World-Physics-Everyone/dp/0674...

palish• 15 years ago

I'd encourage everyone to read Einstein's book on relativity: http://dl.dropbox.com/u/315/books/Albert%20Einstein/Albert%2...

His writing style is beautifully simple and the content is therefore easy for anyone to read and understand.

reledi• 15 years ago

I thought I was viewing a PDF at first, the style is so neat. Does anyone know if it was converted from LaTeX to HTML?

Scaevolus• 15 years ago

According to a meta tag, it was generated by Amaya-- http://www.w3.org/Amaya

brianpan• 15 years ago

Yeah, I was fooled too for a couple of hours. It's very strange to translate pages so literally to the web.

mbateman• 15 years ago

John Norton (the author) is an amazing historian and philosopher of science. People might be interested in some of the other "goodies" on his website -- http://www.pitt.edu/~jdnorton/Goodies/ -- and perhaps some of his papers as well.

Einstein for Everyone

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