A few random science questions

[Ulyaoth]

A few things I've always been confused about.

First, waves, do waves of either light or sound actually travel going up and down as you travel? Or is it some kind of representation of something like where there's protons and the down part is a gap or something?
Also, if sound is just a pressurization of air or water or whatever, how come the waves don't get messed up if more than one frequency or amplitude is in the same spot at once? They don't like cross and mess each other up?
And how does light hold information? I don't understand how a stream of particles can hold tons of information.

And do any scientists believe in a cyclic universe? Whenever I heard people talk about the universe it seems that all scientists think the universe will just expand forever until all matter is so far apart that the universe would become completely stable as all energy is too spread out to do anything. This just doesn't make sense to me that the universe could have just been created one day, that the laws of physics could have been created and not always existed, and I don't get why it seems no one believes that the universe might expand to a certain point then just start falling back to a central point to do a cyclic big bang.

[TheKwas]

Sounds wave do actually oscillate around a fixed position, if I understand correctly, but I'm not sure if the same applies to light-waves.

Also, if sound is just a pressurization of air or water or whatever, how come the waves don't get messed up if more than one frequency or amplitude is in the same spot at once? They don't like cross and mess each other up?

I believe they do actually 'cross and mess each other up'. Take out your electric guitar, crank up the distortion and volume, and play two harmonics of the same note at the same time. You'll get a clean sound despite distortion being turned on. De-tune one of the strings so that the harmonics are of two different notes, and you'll start to hear the distortion. Play your favourite Nirvana song, and that grungy tone is due to the amplified distortion typical of grunge music.

Many guitar players who have trouble hearing tones by ear naturally will actually use the harmonic & distortion method to tune their guitars without relying on a tuner device.

And do any scientists believe in a cyclic universe? Whenever I heard people talk about the universe it seems that all scientists think the universe will just expand forever until all matter is so far apart that the universe would become completely stable as all energy is too spread out to do anything

It's not a popular belief because there's no real known mechanism that could drive a 'big crunch' given the observations astronomers have gathered.

However, there is some new interesting speculation (based off string theory) coming out that may lead to such a mechanism being discovered. News snip:

Neil Turok: In our picture, there was a universe before the Big Bang, very much like our universe today: a low density of matter and some stuff called dark energy. If you postulate a universe like this, but the dark energy within is actually unstable, then the decay of this dark energy drives the two branes together. These two branes clash and then, having filled with radiation, separate and expand to form galaxies and stars.

Then the dark energy takes over again. It's the energy of attraction between the two branes: It pulls them back together. You have bang followed by bang followed by bang. You have no beginning of time. It's always been there.

And for the string theory skeptics out there, there might even be ways to falsify this dark energy theory:

Turok: If the universe sprung into existence and then expanded exponentially, you get gravitational waves traveling through space-time. These would fill the universe, a pattern of echoes of the inflation itself. In our model, the collision of these two branes doesn't make waves at all. So if we could measure the waves, we could see which theory is right.

Stephen Hawking bet me that we'll see the signal from inflation. I said that we won't, and he can take it for any amount of money at even odds. So far he hasn't named an amount. He's richer than me, so he's being nice.

http://www.wired.com/science/discove...08/02/qa_turok

This just doesn't make sense to me that the universe could have just been created one day, that the laws of physics could have been created and not always existed, and I don't get why it seems no one believes that the universe might expand to a certain point then just start falling back to a central point to do a cyclic big bang.

You're on the verge of opening a can of confusing worms. It's a bit misleading to say that the universe was 'created', because that indicates there was something 'before' the universe. However, time and space are, on a physical level, the same thing, so the creation of space was also the creation of time. To talk about before the big bang is to talk about being South of the South pole. It's a nonsense topic.

The Universe is all there is, the all there ever will be, and the all there ever was, because the Universe is everything, including time.

If you want to complicate the issue more, you should consider the fact that our perception of time isn't an objective perception of it. Human brains see time as 'flowing' in one direction because human brains have to obey the laws of thermodynamics; Specifically, human brains have to experience entropy.

If you imagine the brain as a series of on and off switches (which is how computer chips work), in order for the brain to process anything, it needs to turn a switch on (or off). To do this requires actual energy to actually physically move the switch from off to on. This focus of energy to increase 'order' (using the term loosely) has to be offset by a greater dispersion of energy elsewhere (disorder). This movement from ordered energy to disordered energy (using the terms very loosely, again) is called entropy. Somewhat similarly, I can smash a teacup into many fine bits without much work, but I would find it impossible to reverse the damage with the same ease. Teacup-smashing is one directional: the direction of entropy.

However, just because our brains need to move along through time with entropy doesn't mean that time itself is flowing. Time can be interpreted to be static, with neither end or beginning and thus, no 'creation'.

If it helps, you can imagine yourself running down a tunnel through giant picture frames. In the first picture you run through, there's a spider who has laid out one line of silk. In each proceeding picture, the spider finishes more and more of its web until finally it's finished with a giant, beautiful web. If you run fast enough, you can even make it look like a motion picture.

After watching this short movie, you are likely to conclude that you started at the beginning and now you're at the end of the tunnel. However, another runner who started at the other end of the tunnel could have watched the same movie in reverse and concluded that the spider ate it's own web (which spiders do), and that HE started at the beginning. Of course, there is no 'beginning' or end, as there's just a bunch of physical pictures in a tunnel. What you proscribe as a 'beginning' is based purely on how you perceived it, not on the objective nature of the tunnel. There's just a tunnel with two ends, plain and simple.

Who's to say that the big bang was the beginning? Perhaps there are magical ghost creatures that can avoid entropy and infact travel through time against entropy. They would conclude that the big bang is the ending.

Anyways, that's an amateur science rant from an eco major. I'm sure the actual scientists here will correct out the (probably numerous) mistakes I've made myself.

[Simetrical]

First, waves, do waves of either light or sound actually travel going up and down as you travel? Or is it some kind of representation of something like where there's protons and the down part is a gap or something?

Light waves do go up and down as they travel: they're transverse waves. Specifically, a light wave consists of an electric and magnetic field, which are always perpendicular to each other as well as to the direction of propagation. (You can see from this that light is intrinsically a three-dimensional phenomenon.) The physical meaning of "going up and down" is that the direction of the electric field oscillates perpendicular to the direction of motion with a frequency given by the light's frequency, and likewise for the magnetic field's direction. The direction of a magnetic or electric field is of course what determines how objects move in it, and is of basic physical significance to the field.

Sound waves are physically somewhat different in a number of ways. They're longitudinal, not transverse: the individual particles do not oscillate perpendicular to the direction of wave propagation, but parallel to it. (Actually, when I was double-checking some stuff on Wikipedia, I saw that sound waves are partly transverse when traveling through solids, but never mind.) You can think of this like a field of marbles or cue balls, with some at the end being pushed into the others. They'll hit the ones next to them, then bounce back, hit the ones behind them, bounce back, hit the ones forward of them again, and so on. This is probably not a terribly accurate picture, but it suffices.

One interesting point about sound is that the actual particles are not disturbed much from their positions, they just transmit some kinetic energy, and that's what marks the progress of the wave. You can see this experimentally by yelling through some smoke or something: the smoke is barely disturbed, despite a loud sound passing straight through it.

Also, if sound is just a pressurization of air or water or whatever, how come the waves don't get messed up if more than one frequency or amplitude is in the same spot at once? They don't like cross and mess each other up?

Well, you can't have more than one amplitude in one place at once. In sound waves, the amplitude at a point is simply the pressure at that point, and the pressure at any given point in a fluid is more or less unique. Frequency is not a property of any particular location, but a property of the wave itself, so you can't exactly have two frequencies in one place.

But the basic question is, do different sound waves that pass through the same point at the same time interfere with each other? The short answer is yes, they interfere with each other in that the sound at the point where they overlap is different; but no, they do not interfere with each other once they pass the point of intersection. And this is true of all waves.

The somewhat longer answer is that the wave equation is a linear differential equation. What this means mathematically is that given any two solutions to the equation (any two waves), their sum is also a solution (also a wave). Physically, what this means is that if two waves overlap, you add their amplitudes together, and nothing else happens. So if two waves pass through a single point at a given time, you just add their amplitudes together for that point, and do the same for all other points in space-time where they intersect. Where they don't intersect, that is, where one of them is zero, the other is unchanged, because you just add zero to it (the value of the other at that point).

One immediate corollary is that it's possible for two waves to cancel if their amplitudes are opposites. You can arrange light so it does this at some points: it's a typical freshman physics experiment. It's also possible to do for sound, which is what sound-cancelling headphones try to do (they detect nearby sound and try to emit the exact opposite). Unfortunately it's a bit tricky to get really good cancellation this way: you'll usually have some negative interference (cancellation) and some positive interference (it becomes louder/brighter).

As for the effect of frequency, when you add together two waves of different frequencies, what you get is a wave with multiple frequencies. For instance, pure red light has one frequency, pure blue light has another, but if you add them together you get both frequencies at once, not some intermediate frequency. If you know some calculus, it's easy to see from the wave equation that not all waves are periodic, although that may seem odd as far as your intuitive notion of a wave. It immediately follows that trying to assign all waves a frequency is futile. A common task in various types of wave analysis, like with spectrometers, is to split up a wave in terms of the amplitude of its frequency components. For light, you would have a chart saying how much the amplitude is for red light, how much for orange, and so on, at whatever precision you like.

And how does light hold information? I don't understand how a stream of particles can hold tons of information.

"One if by land, two if by sea!" It's really no more complicated than that. There are a lot of variations, but to give you the idea, a basic tactic is just to turn the light on to transmit a one bit, and turn it off to transmit a zero bit. You can also shine it brighter to transmit a one, and dimmer for a zero (amplitude modulation, used by AM radio); make it red for a one and purple for a zero (frequency modulation, used by FM radio); and many other schemes.

And do any scientists believe in a cyclic universe? Whenever I heard people talk about the universe it seems that all scientists think the universe will just expand forever until all matter is so far apart that the universe would become completely stable as all energy is too spread out to do anything. This just doesn't make sense to me that the universe could have just been created one day, that the laws of physics could have been created and not always existed, and I don't get why it seems no one believes that the universe might expand to a certain point then just start falling back to a central point to do a cyclic big bang.

This is commonly called the Big Crunch hypothesis. It's on the table. The fact of the matter is, nobody really is sure yet about anything before the beginning of the universe, or its ultimate fate.

Sounds wave do actually oscillate around a fixed position, if I understand correctly, but I'm not sure if the same applies to light-waves.

The individual particles affected by a sound wave do oscillate around a more or less fixed point, yeah. There are no particles involved in light waves, classically, so the distinction doesn't make so much sense in that model. (There are photons, of course, which definitely do not oscillate about a fixed point: they move in one direction.)

I believe they do actually 'cross and mess each other up'. Take out your electric guitar, crank up the distortion and volume, and play two harmonics of the same note at the same time. You'll get a clean sound despite distortion being turned on. De-tune one of the strings so that the harmonics are of two different notes, and you'll start to hear the distortion. Play your favourite Nirvana song, and that grungy tone is due to the amplified distortion typical of grunge music.

Many guitar players who have trouble hearing tones by ear naturally will actually use the harmonic & distortion method to tune their guitars without relying on a tuner device.

I don't know much about music and so don't really understand the effect you're talking about. I believe it's probably just a mechanical artifact of the guitar, rather than an intrinsic property of sound. The appropriate analogy for interference is more like two separate guitars, being played near each other so their sound waves overlap.

However, just because our brains need to move along through time with entropy doesn't mean that time itself is flowing. Time can be interpreted to be static, with neither end or beginning and thus, no 'creation'.

"Static" means, by definition, "not changing in time". The idea of time changing is meaningless if you don't define what it's changing relative to. In physics, and generally anything using calculus, it's explicit: you discuss rates of change with respect to time, or with respect to any other quantity. Rates of change without a referent are meaningless. Of course, the rate of change of time with respect to itself is one, not zero.

The subjective impression of time is a somewhat separate issue. We classify the future as being the direction of increasing entropy, and that's just a definition. You can of course define the opposite, but you've accomplished nothing but using a confusing definition. There's nothing profound in your entropy-reversing ghosts: they're perceiving the same physical phenomena but calling them different things and maybe thinking of them differently. It's not an interesting physical issue, it's maybe a psychological one. The issue of why entropy is just about the only process that's non-invariant under time reflection, and what ramifications that has, is quite an interesting thing.