alaina: plastic tubes and pots and pans

I've always loved science. I love science just as much as I love literature, which is to say... um... I love science a lot.

I should stop here and point out that I like exercising my brain. One of the reasons I like non-classical theoretical physics so much is that it's a real mental workout to try to understand it. A lot of it--actually, most of the neat stuff--is not particularly intuitive, at least not if you don't have any background in it. (Dammit, Jim, I'm a computer person, not a theoretical physicist!) So, for me, the more abstract, weird and non-intuitive the subject is, the more I enjoy learning about it.

For several years I was hooked on human biochemistry. I still am to a great degree, but it's not an interest that I am actively developing any more. I've also been really into organic chemistry, but that has led me back to atomic physics, which led me to quantum mechanics. I was puzzled by why QM doesn't really seem to do anything useful with gravity, which is the coolest of the four known forces. That made me research quantum gravity, where I have over the years started to learn about loop quantum gravity and string theory. I don't so much care about LQG, but string theory captured my fancy. When I first figured out that string theorists are saying that matter is made of little vibrating strings of energy I was hooked, and I've been into string theory for the last couple of years.

Somewhat out of sequence, string theory has led me back to relativity, which I skipped over in favour of what I saw as more interesting (and fucked up) quantum mechanics. Relativity is actually way easier to grok than QM. I think I'm finally starting to get relativity; I am developing an intuitive understanding of special relativity, and I get what general relativity is trying to say even though I don't yet understand how Einstein reached his conclusions; specifically I don't know how he used Riemannian geometry to derive his equations for curved spacetime. I'm kicking myself for taking this long to get into relativity because it's pretty twisted and very very interesting.

I'm continuing to learn about relativity and quantum mechanics in the hope that I can eventually get to string theory. I don't remember when or how I first heard about string theory, but it was at least ten years ago when I was living in California. I do know that Brian Greene's The Elegant Universe was my first in-depth introduction to string theory, though I did read some websites and Lee Smolin's Three Roads to Quantum Gravity before I picked up Greene's book in May of 2003. I've decided afiter reading everything I can find about string theory--and after talking to a string theorist--that I need to step back and work on relativity and QM before I really try to tackle string theory.

For those who are interested and want an even more accessible popular introduction to relativity, QM and string theory, The Elegant Universe was presented as NOVA miniseries that was first shown in 2003. You can buy it on DVD and VHS now. I've already gotten my copy!

Learning for me is an iterative process whereby I have to view problems from several different angles, and have information presented to me in different ways, for me to really *get* it. One of those ways is repeating what I learn; another is asking questions that I can answer for myself later.

Below is a list of questions I hope to answer in my investigations of theoretical physics, along with quotes from authors or speakers that really stand out for me.

It is entirely possible that these are stupid questions and oversimplified quotes. You should not consider this page a source of authoritative or even useful information. If you're going to email me to correct me, that would be great, but please remember that I am not pretending to be an expert; I'm just learning, and I'm doing it all on my own without anybody teaching me so it's slow going!

As of this most recent update I think I've gotten most of the answers to my own satisfaction, but I think I'm going to leave them up as a way to track my progress.

Questions & Observations

Quotes

What if direction of time isn't relevant, but entropy is? i.e., time can move backwards but entropy cannot decrease - a simple explanation for why eggs break but don't unbreak. (A: Brian Greene discusses this in The Fabric of the Cosmos. Entropy could increase irrespective of the direction of time. More on this later.)

Why does string theory prefer compactified dimensions to expanded dimensions? Is it possible that there is a combination of both?
How does general relativity derive curved space from special relativity's flat space? (A: Einstein demonstrated that the coordinates in spacetime of an accelerating observer would change with the observer's changes in speed and direction, and that these changes fit perfectly within a Riemannian geometry of a curved space; acceleration creates spacetime that is warped. Using the eqivalence principle, Einstein then surmised that if this is true for acceleration it is also true for gravity.) I now need to learn why Riemannian geometry led to that conclusion. First I need to learn Riemannian geometry. :)
Is it possible that, once we understand the extra dimensions, we can train ourselves to percieve them, or "parallel" dimensions in the universe-on-a-membrane theory, or are we genuinely unable to intuitively understand movement in spatial dimensions greater than three?
Entanglement: how does string theory address entanglement? Are branes connected over long distances, or are all of the branes actually one big brane with lots of localized oscillations?
How is spacetime derived from strings, rather than strings being in spacetime?
Is there a 1:1 correspondence between particles and strings? i.e., one string == one particle/quanta?
Do strings interact with one another at string level? i.e., smashing into one another, causing interference, etc. If so, what does that do?
Are there strings that don't have corresponding quanta?
Are the extra dimensions different than the X, Y and Z spatial dimensions? Are they at right angles to one another?
Are there a finite number of string modes?
Can strings change modes?

The Fabric of the Cosmos, Brian Greene

Nothing in the equations of fundamental physics shows any sign of treating one direction of time differently from the other, and that is totally at odds with everything we experience. (p13)

Special physical conditions at the universe's inception (a highly ordered environment at or just after the big bang) may have imprinted a direction on time, rather as winding up a clock, twisting its spring into a highly ordered initial state, allows it to tick forward. (p13)

An object's velocity can be specified only in relation to that of another object. (p24)

(Leibniz claimed that) without the objects in space, space itself has no independent meaning or existence. Think of the English alphabet. It provides an order for twenty-six letters--it provides relations such as a is next to b, d is six letters before j, x is three letters after u, and so on. But without the letters, the alphabet has no meaning--it has no "supra-letter," independent existence. Instead, the alphabet comes into being with the letters whose lexicographic relations it supplies. Leibniz claiemd that the same is true for space: Space has no meaning beyond providing the natural language for discussing the relationship between one object's location and another. According to Leibniz, if all objects were removed from space--if space were compeltely empty--it would be as meaningless as an alphabet that's missing its letters. (p30)

In Mach's way of thinking, only relative motion and relative acceleration matter. You feel acceleration only when you accelerate relative to the average distribution of other material inhabiting the cosmos. Without other material--without any benchmarks for comparison--Mach claimed there woudl be no way to experience acceleration. (p37)

Space, in Mach's view, is very much as Leibniz imagined--it's the language for expressing the relationship between one object's position and another's. But, like an alphabet without letters, space does not enjoy an independent existence. (p37)

The speed of light, Einstein declared, is 670 million miles per hour relative to anything and everything. (p45)

Einstein... forcefully argued that regardless of how fast you move toward or away fro ma beam of light, you will always measure its speed to be 670 million miles per hour--not a bit faster, not a bit slower, no matter what. (p45)

In fact, the revolutionary discovery of special relativity is this: When you look at something like a parked car, which from your viewpoint is stationary--not moving through space, that is--all of its motion is through time. (p48)

Special relativity declares a... law for all motion: the combined speed of any object's motion throuhg space and its motion throguh time is always precisely equal to the speed of light. At first you may instinctively recoil from this statement since we are all used to the idea that nothing but lgiht can travel at light speed. But that familiar idea refers solely to motion through space. (p49)

In 1971, Joseph Hafele and Richard Keating flew state-of-the-art cesium-beam atomic clocks around the world on a commercial Pan Am jet. When they compared the clocks flown on the plane with identical clocks left stationary on the ground, they found that less time had elapsed on the moving clocks. The difference was tiny--a few hundred billionths of a second--but it was precisely in accord with Einstein's discoveries. (p50)

Einsteins' theory does not proclaim that everything is relative. Special relativity does claim that some things are relative: velocities are relative; distances across space are relative; durations of elapsed time are relative. (p51)

Absolute space does not exist. Absolute time does not exist. But according to special relativity, absolute spacetime does exist. (p59)

If the trajectory an object follows through spacetime is a straight line... it is not accelerating. (pp60-61)

All this led Einstein to conclude that the force one feels from gravity and the force one feels from acceleration are the same. They are equivalent. Eisntein calld this the principle of equivalence. (p67)

Clearly, this is a radically different way of thinking about motion. But it's anchored in the simple recognition that you feel gravity's influence only when you resist it. By contrast, when you fully give in to gravity you don't feel it. Assuming you are not subject to other influences (such as air resistance), when you give in to gravity and allow yourself to fall freely, you feel as you woudl if you were freely floating in empty space--a perspective which, unhesitatingly, we consider to be unaccelerated. (pp67-68)

[Einstein] found that warps and ripples [in space]--gravity, that is--do not travel from palce to place instantaneously, as they do in Newtonian calculations of gravity. Instead, they travel at exactly the speed of light. Not a bit faster or slower, fully in keeping with the speed limit set by special relativity. (p72)

According to general relativity, the benchmarks for all motion, and accelerated motion in particular, are freely falling observers--observers who have fully given in to gravity and are being acted upon by no other forces. (p73)

In an empty unchanging universe--no stars, no planets, no anything at all--there is no gravity. And without gravity, spacetime is not warped--and that means we are back in the simpler setting of special relativity. (p74)

Although the issue is still debated, as we've now seen, the most straightforward reading of Einstein and his general relativity is that spacetime can provide such a benchmark: spacetime is a something. (p75)

(Quantum mechanics says that) we can't ever know the exact location and exact velocity of even a single particle. We can't predict with total certainty the otucome of even the simplest of experiments, let alone the evolution of the entire cosmos. Quantum mechanics shows that the best we can ever do is predict the probability that an experiment will turn out this way or that. And as quantum mechanics has been verified through decades of fantastically accurate experiments, the Newtonian cosmic clock, even with its Einsteinian updating, is an untenable metaphor; it is demonstrably not how the world works. (p79)