Independence Day

[Student of Trinity]

What's stuff made of?

[Dikiyoba]

More stuff.

 

Dikiyoba.

[Erebus the Black]

The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. Less than 5% of the universe is ordinary matter, a relatively small contribution.

And as you can see, no aether.

[Dikiyoba]

Originally Posted By: Erasmus

And as you can see, no aether.

You missed Dantius' joke. Although that is an interesting graph.

Dikiyoba.

[Dintiradan]

So, does anti-stuff exist?

 

(Also, anyone else have a certain George Carlin routine stuck in their heads?)

[Karoka]

There's no aether on that chart because I hid it. You'll never find it.

 

EDIT: Ever.

[Erebus the Black]

In fact you might consider the sea of electric and magnetic fields we live/swim in as "aether" as they are the medium through which light propagates through. None the less a light wave/beam can also propagate through an area where those fields are (without figuring(including it in our calculation) for the beam ) 0, unlike other waves, such as sound (meaning sound cannot propagate where there is no matter).

[Student of Trinity]

The 'luminiferous ether' (or 'aether') has an interesting history. Clark Maxwell believed in it quite literally, and described it as 'the largest object' in the universe, since it was everywhere. He had a point; since it was everywhere, and continuous, there was really only one of it. It was not so much a kind of stuff, as a single thing. But I once found a semi-popular encyclopedia-like volume from the turn of the 20th century, which had a very sound discussion of the ether, and took an agnostic view about its reality. So it's not true that everyone believed in it until Einstein overthrew it.

 

The ether was supposed to answer the question, What are electric and magnetic fields made of? (Hence, after Clark Maxwell: What is light made of?) The answer wasn't precisely that they were made of ether. Rather, the fields were supposed to represent stresses and strains in the ether, like the stresses and strains in a piece of metal under load. Light (electromagnetic waves) was then simply sound, travelling in ether.

 

The ether was not so much disproven as forgotten. We came to realize, as someone put it, that the ether really only existed in order to provide a subject for the verb 'oscillate'. In order to conform to observations, it had been defined into unobservability. At some point, Hertz declared that 'Maxwell's theory is Maxwell's equations.' At the time this was a radical statement: it was the purely mathematical field equations that constituted the physical theory, all by themselves; they were not simply a corollary to some underlying theory about the material properties of ether. Until that time, physics had been all about matter. Suddenly it was accepted that a purely formal description might be correct in itself. Today, Hertz's statement seems like a tautology.

 

By now, in fact, form has essentially won. I can tell you that matter is made of various fundamental particles, but if you ask me what those particles are made of, I simply cannot answer. We have no idea. We just have equations governing how the particles move, interact, appear, and disappear.

 

We can say some more about what they are like, though. For instance, an electron is not just a tiny point with an electric charge. Tiny point charges do exist, but they are not exactly electrons. Tiny opposite point charges exist, too, but these are not exactly positrons. Vacuum — the lowest energy state of the universe — is empty of electrons and positrons, but it is not empty of point charges. Vacuum is a sort of quantum plasma of positive and negative point charges, almost evenly distributed, so that unless you look on a very fine scale, it just looks neutral. But if you can get spatial resolution on scales finer than about 10^(-12) meters, which is about 1% of the radius of a hydrogen atom, you will see the seething sea of opposite point charges, even in the purest vacuum.

 

Having an actual electron means having one extra negative point charge. Its electric field also distorts the distribution of all the paired-up positive and negative charges around it. What we call an electron is the one extra charge, plus the distortion of the vacuum distribution that follows it around.

 

In classical physics terms, space itself is a dielectric: neutral on average, but full of opposite charges on finer scales, and thus polarizable. So quantum electrodynamics has in a sense brought back the ether, after all. It is just a bit stranger than Maxwell realized.

[Lilith]

It strikes me that although we say that fundamental particles exhibit both wave-like and particle-like behaviour, what we really ought to say is that macroscopic particles exhibit a subset of wave-particle-like behaviour, and macroscopic waves exhibit another subset. Describing more fundamental things in terms of less fundamental things seems bound to produce incomplete analogies.

[Alorael at Large]

Yes, but the wave-particle duality came up when physicists first worked out that there was not a neat binary choice, and it persists because it's easier to explain to students starting in terms of things they already understand or can readily understand by observation: blocks of stuff and wiggling strings.

 

—Alorael, who imagines it's also easier on the physicists. No matter how much you work at the quantum level, it can't ever really be easy to wrap your mind around tiny wave-particles. Mind you, that's mostly because even when you have wrapped your mind around them there's a non-zero probability that they're outside your mind anyway. Unless your mind is a one-dimensional box, of course, but those kinds of minds tend not to make it to quantum mechanics anyway.

[Skwish-E]

I'm bored now ...

[Erebus the Black]

Another interesting thing is that light is in fact composed of three waves: an electric field disturbance, a magnetic field disturbance, and the "location probability" wave function (I tried to translate it from my own language).

Which is more waves than any other particle or wave I know of

[Niemand]

It's usually more practical (for particle physics, at least) to treat the electromagnetic filed as a single entity, and usually to work with the potential Aµ, which has four components, rather than the field, which appears as a tensor with six (seemingly) independent components. (I can't find a way to get UBB to do a superscript, so I guess we'll have the covariant 4-vector potential.)

[Student of Trinity]

Erasmus, I'm afraid this is kind of confused. There is no really good way to talk about a wave function as part of a light wave. Quantum mechanics applies to light, all right, but not in that way.

[Erebus the Black]

That is what I understood from my quantum mech. course, what I didn't understand was how much of a (n infinite) light wave is a photon?

[Randomizer]

A photon is the component particle representation of a light wave. What you think of a light wave consists of many photons moving together.

 

Some experiments, the classical double slit experiment is an example, reduce the number of photons to a slow enough rate where only one photon passes at a time so the particle behavior can be observed and show that as the number of photons increases you can see the wave behavior as the result of many photons.

[Dintiradan]

(It's been a long time, but isn't the distribution phenomenon still observed with only one photon?)

[Niemand]

It is, which is where the weirdness of quantum mechanics shows through: the wave behavior is not that of the bulk material or group of particles (like sound waves or ocean waves) but arises from the wavefuction which describes each individual particle's state.

[Erebus the Black]

Originally Posted By: Randomizer

A photon is the component particle representation of a light wave. What you think of a light wave consists of many photons moving together.

Yes, but how many? (I asked how much of a light wave is a photon, you answered a light wave is made out of many photons but didn't say how to figure out how many which would be the answer to my question) I mean, Ep = hf, Ewave=? How many wave periods constitute a photon? (or the other way around), and beyond that I know a photon has a "location distribution" wave function (which you get a look at with young's slit experiment) which differs from it's Electromagnetic wave function.

[Randomizer]

There are two different things. The energy associated with the wavelength of a photon is what you have in the equation:

 

Ep = hf

 

where f is the frequency and h is Plank's constant. This is how much energy each photon has to transfer. A light wave can consist of multiple photons and the sum of those photon energies is the energy of the wave.

 

This is the difference in the power of a light source. A dim light and bright light can have the same frequency (wavelength) but different powers meaning more photons are being given off.

[Student of Trinity]

Randomizer is right.

 

My point is: what you normally learn in intro quantum courses is single particle quantum mechanics, and that's very misleading in a critical way. With one particle, you can think of the wave function as a field, like the electric field for example. You can think of it as some complex number living at every point in space.

 

But the problem is this. With one particle, you can write a wave function as a function of its position: f(x). With two particles, what do you do? The answer is that the wave function is now f(x1,x2), a function of two positions. With a zillion particles, the wave function propagates in a space of three zillion dimensions (if each position is three-dimensional).

 

In other words, the wave function lives not in three-dimensional space, but in your system's configuration space. It's just a co-incidence that for a single particle these two spaces look the same.

 

With photons, even the single-photon picture is complicated by the fact that photons are massless. The basis of photon position eigenstates is just never really a useful one, even with just one photon. But it's worse than this, because photons are not conserved. They're created and destroyed all the time, and so it's actually technically extremely difficult to produce single-photon states. People are still working on being able to do that reliably. So normally you have not one photon, but zillions, as Randomizer suggested. And that means you're talking about that really large configuration space, rather than ordinary space.

 

 

So to understand the quantum nature of light waves, you really need not just quantum mechanics, but quantum field theory.

[Dantius]

And I thought that Black-Scholes was the most complicated math I'd have to deal with today, and then I walk in here and it's tensors and wave equations and Lagrangians or Hamiltonians or whatever it is you QM people call them all over the place.

 

Price of admission into a game board where the majority of members have an advanced college degree, I guess...

[Randomizer]

Originally Posted By: Dantius

Price of admission into a game board where some members have an advanced college degree in physics, I guess...

FYT

[Sarachim]

Originally Posted By: Randomizer

Originally Posted By: Dantius

Price of admission into a game board where some members have an advanced college degree in physics, I guess...

FYT

Maybe we historians will make our own thread, and not invite the physicists.

[nikki.]

And maybe us English students will weep in the corner having picked a discipline that is of neither use nor ornament.

[Karoka]

Originally Posted By: Shelagh

And maybe us English students will weep in the corner having picked a discipline that is of neither use nor ornament.

You should have picked Spanish.

[Alorael at Large]

Physicists might not be experts in history, but they more or less know the language and can sound intelligible, if not especially groundbreaking. English, or more specifically lit-crit, has its own jargon, but it can be mimicked without too much difficulty. Spanish really is the tough one, but again, it's hard to distinguish between a degree and simple fluency.

 

If you do not know what a tensor is, how an operator operates, whether the equation is time-dependent or not, how curved your spacetime is, or how many dimensions of vibrating strings you're talking about, you really can't fake physics.

 

What you need isn't just your own conversation. You need your own jargon!

 

—Alorael, who probably could have just posted xkcd and been done.

[Aoslare]

What do you actually get from a Spanish degree beyond simple fluency?

[Student of Trinity]

Enhanced ability to anticipate the Spanish Inquisition (+1 on roll, once per day).

[Aoslare]

+1 on a roll that automatically fails...?

[Dantius]

Originally Posted By: CRISIS on INFINITE SLARTIES

What do you actually get from a Spanish degree beyond simple fluency?

That's rich comic from a linguistics major, since the only legitimate reason for getting a degree in the subject are the same- to pursue a PhD so you can teach the subject to others.

[Aoslare]

I didn't mean it quite like that. Linguistics is about as non-directly practical as degrees get, it's true. Spanish is way more practical, hands down. The question is what, if anything, you actually learn beyond the language.

[Dintiradan]

I've always assumed that such degrees would also introduce you to the major literary works of that language, both historical and contemporary. Say, assigned readings from Gabriel García Márquez?

[Alorael at Large]

A degree in English requires proficiency in English, familiarity with literature generally and English literature specifically, and some familiarity with the cultures that have produced literature in English. A degree in any other language is much the same, except more effort gets spent on learning the language if it's not your first.

 

—Alorael, who doesn't think that the degree requires anything approaching fluency at a native level. You need to be able to read and speak and understand fairly well and fairly quickly, but not perfectly.

[nikki.]

My brother actually did a joint honours degree in Spanish and History. I didn't really pay enough attention to what he was studying but I do know that after learning the language, the Spanish side was mainly a study of Spanish literature, with some politics and culture thrown in too. And, of course, there were modules that related to both Spanish and History.

 

 

[Aoslare]

Originally Posted By: Out of the loupe, out of sight

A degree in English requires proficiency in English, familiarity with literature generally and English literature specifically, and some familiarity with the cultures that have produced literature in English. A degree in any other language is much the same, except more effort gets spent on learning the language if it's not your first.

This is blatantly untrue and you know it. The course requirements for an English degree typically revolve around higher level reading and writing activities: analyzing and interpreting texts, how they are structured and how to create your own. You are likely to get lots of practice writing formal and personal essays, possibly even formal rhetorical training. And you'll spend lots of time learning about how other people think particular texts should be interpreted.

Foreign language degrees do not involve systematic studies of methods for processing written language, like that.

[Skwish-E]

Ha ha!! Academician fight!!

[Alorael at Large]

Really? The people I know who got degrees in Russian, Spanish, and German all had to analyze and interpret texts. They didn't create their own literature, but that's never been a requirement for an English degree either; they did, of course, write their own analyses and criticisms. Yes, these were formal and personal essays, often involving reading and arguing with or against the academic literature on the subject in question.

 

The critical difference is, as I said, that many degrees in foreign languages don't require the same proficiency in those languages that an English degree assumes in English. Some—not all, but in some cases a substantial amount—of the reading for those foreign language degrees was in English.

 

—Alorael, who thinks that Slarty's requirements for English are, in fact, fairly similar to the baseline requirements for (good) humanities degrees in general. You have to be able to read, analyze, critique, interpret, synthesize, both from primary sources and academic treatment of those sources, and then produce writing based on all that. That's how academic humanities work.

[Student of Trinity]

It's still a problem that if you start learning a language in your first year of college, you're not going to be able to catch up to university-level proficiency in that foreign language within four years. You probably end up getting a bachelor's degree for capability comparable to that of a good high school graduate in your new language.

 

That's maybe fair enough; learning a foreign language is a very different thing from training in your mother tongue. But that's the thing.

[Alorael at Large]

But you also have something very similar to an English degree, except your concentration is in a specific foreign literature, some amount of which is in translation. You still have the literature and writing skills, and you have some knowledge of a foreign language.

 

—Alorael, who wants a degree in procrastination. It's a very useful life skill in many circumstances, and it will aid you in a wide variety of professions. He's done fine with his amateur efforts, but with a good education he could do much better.

[The Ratt]

You've just never got around to getting one, right?

[Aoslare]

Well, I still disagree. And since neither one of us has any actual evidence, just assertions, we may need to remain in disagreement.

[Student of Trinity]

I took English courses as an undergrad, and worked my way up to writing a senior mini-thesis on Paradise Lost. I took only one English course per semester, instead of the three an English major would have taken, but my impression was that I could easily have taken three times as many courses, and still not have hit badly diminishing returns on my investment in learning to read and write.

 

Writing well is really hard. Reading good writing improves your own writing, as you figure out what they did right. Writing well also improves your ability to grasp the point of badly written texts, which are most texts. You learn to paraphrase things into the way they should have been put. I'm not sure somebody who has scraped through a bachelor's degree in English has necessarily attained all of that, but somebody who really did well has become an intellectual force.

 

Even with less than a minor concentration in English, I'm serving now as a sort of secret weapon in our department's application for a giant collective grant. It's partly just that the application has to be in English, and everyone else is fluent but non-native. But it's more than that; I'm taking disjointed chunks of jargon-laden prose, and reforging them into a coherent argument. I learned how to do that by writing a lot of little essays about 17th century poems, twenty-five years ago.