The Cassini-Huygens spacecraft is an unmaned vehicle gathering data about Saturn and its various moons. A few years ago, it sent back the following transmission:
What's going on there??? The answer is the Northen Lights, except the north of Saturn, rather than Earth.
The Sun spits out a huge number of electrically-charged, radioactive particles in all directions with a significant amount of force. It's called solar wind and you can picture it like a river of energy flowing from the surface of the Sun.
When electrically charged particles (like those in the solar wind) interact with magnetic fields they get deflected. On Earth, most of these particles are specifically directed to the north and south poles, where the magnetic field points. When these particles start flying into the Earth, they get mixed up in the ionosphere, Earth's very own electrically-charged bubble. The resulting mixture of electric and magnetic interactions causes the Northern Lights (Aurora Borealis) or the Southern Lights (Aurora Australis). But Earth is not unique.
Jupiter and Saturn have their own magnetic fields, and their own ionospheres (Uranus and Neptune probably have them too) which means solar wind does the same thing to them, creating the same beautiful light displays. But not all of light is visible. Some of it falls in the very low-energy part of the light spectrum: invisible radio-waves. These radio waves aren't picked up by our eyes, but to a probe like Cassini, they're a beautiful symphony.
What's happening in that video is that Cassini is picking up on radio waves from the North (or possibly South) pole of Saturn. Those radio waves can then be converted into audio sounds for the human ear. In other words, Saturn is acting like a radio station, pumping out its own surreal music. The resulting radio-to-audio waves are what you're hearing in the youtube clip!
Here's the thing, an ice cube does not "give out" coldness. There's actually no such thing as coldness. What it really does is absorb heat that's already there. The laws of thermodynamics tell us that a substance at a higher temperature will gradually lose heat to a substance at a lower temperature. Since ice cubes are usually put into a drink when they are about 0 degrees C, the liquid they are suspended in will lose heat to them. What this does is raise the temperature of the ice cube and lower the temperature of the surrounding liquid. The result is a temperature somewhere in between but one in which the heat is more evenly distributed.
What we can now do is a neat little trick using the zeroth law of thermodynamics which is to remove the liquid from the equation. If A (the air) can exchange heat with B (the liquid) and B can exchange it with C (the ice cube) then A is effecitvely exchanging heat with C. So what we're talking about is an ice cube in summer compared to one in winter. Now the question becomes a little clearer.
Picture an ice cube sitting on a cold plate compared to a hot one. The hot one will melt first because heat is more readily transferred than in the cold system. But the cold temperature and the hot temperature will go down by the same temperature. Here's what I mean: 20 degree day vs a 0 degree ice cube might reach a thermal equilibrium of let's say 10 degrees. That's a 10 degree change. A 30 degree day vs a 0 degree ice cube of the same size will reach a temperature equilibrium of, say, 20 degrees. In other words, both systems have cooled down by the same amount. The hotter one just did it quicker.
But then the hotter one starts absorbing more heat from the air, so the drink will also "warm up" faster. The cold one will end up cooling down much later, but it will take a lot longer to "warm up" again. Ultimately, in both systems the final result will be identical. An equilibrium will be reached between drink, water and air. If you keep everything the same size, then the amount of difference should be identical. So, by my back-of-envelope calculations, it makes no difference...I think.
At some point in GCSE Chemistry class, the teacher will probably say that all atoms are made of three basic particles: protons, neutrons and electrons. She's right to say so, by the way. The same way a mars bar is made of caramel, chocolate and that wierd foamy stuff. But obviously you could go one level deeper and ask what the chocolate, caramel and foam are themselves made of. And so it goes with atoms.
Yes protons, neutrons and electrons are the atomic ingredients and they're all you need to explain most of Chemistry, but the rabbit hole of particle physics goes a lot deeper my friends.
Protons and Neutrons, the scourge of every GCSE student's life, are made up of smaller particles called quarks (usually pronounced kwark in the UK, but the guy who named them pronounces it kwork, so we should probably do likewise). Quarks come in six different varieties and their combinations are what make up the more familiar protons and neutrons.
But what about the quarks? I hear you say. And what about the electrons? Well the answer is that we're pretty confident these particles are "fundamental" which means they don't have any internal structure. In other words, they are the smallest things.
This starts to broil the brain after a while because to say something is the smallest thing means you couldn't chop it up. If you somehow had a quark in front of you and a quark-knife, you would be unable to slice it in two. Either the quark would resist the chop, or the act of slicing it would cause it to disappear.
There's a whole list of these "fundamental particles" called The Standard Model (I did a song about it once) which describes the properties of these building blocks, but what causes them to be that way we haven't the faintest or foggiest.
Quarks and electrons could be made of smaller stuff, and in fact there are several theories which suggest they might be. The most famous of which is probably M-theory (a version of Superstring theory...which is itself a version of String theory) which argues that fundamental particles can be thought of as tiny vibrating strings made of.......???stuff?? In truth, even asking the question "what is a string made of?" might be a meaningless question, like asking how to melt water, strings are the stuff which make, they are not themselves made.
For the time being though we don't know why quarks are fundamental, what would happen if you tried to split one or why it stops there rather than going on forever. But we've built a hefty machine to help us explore this mystery. The largest man-made machine ever in fact. You might have heard of it.
Although it's sometimes portrayed as an ancient question from the mysterious realms of some temple, the "tree falls" puzzle first appeared in print during the 1880s, so this is actually a late Victorian brainteaser.
Sean (in his question) wanted it to be clear he wasn't being awkward, he really wants to know if there is an answer to the riddle. i'm going to argue that there just might be. The answer all depends on your definition of the word "sound". And this is a very important point to remember about all Philosophy: the answer can sometimes change depending on what the words mean.
The first major philosopher is usually considered to be Socrates. There were earlier ones, but they are referred to, rather tellingly, as pre-Socractic which gives you an idea of Socrates' impact. The philosophical revolution started by Socrates marks a watershed in Western thinking and one of Socrates' most common themes was that defining our terms is key to any philosophical discussion.
Ludwig Wittgenstein, two millenia later, argued that all philosophical discussion was a result of misunderstanding language and that the way we use words are crucial to any discussion on anything. At least I think that's what he was saying, honestly I've read both Wittengenstein's books and I definitely think I understood at least 3% of what he was saying.
Wittgenstein argued that by using words to define other words we'll end up in an eternal loop of never being able to explain or define anything. He was great at dinner parties.
In order to answer the quesiton however, I'm going to say that sound is the result of the following chain of events:
1) An object moves.
2) The air particles are bumped.
3) A pressure wave travels.
4) The eardrum is vibrated by the wave.
5) The brain percieves it.
If a tree falls in the forest, then we've definitely accepted 1, 2 & 3 will happen but 4 & 5 will not. So to boil the question down to its components (a process which philosophers call "logical analysais") we end up with a different question: is the word "sound" referring to a pressure wave of air or the brain's perception of a moving eardrum? If we can agree on what the word sound means then Science can immediately provide an answer.
I would like, therefore, to draw attention to how we use the word sound in other contexts to give us a clue about what we unconsciously mean when we say it.
Supposing a deaf person stood in a room with the television on. Usually we would say "the person can't hear the sound of the TV" but we would very rarely say "there is no sound in that room". Or supposing we put a microphone in a room with a firework going off. We would comfortably say "the microphone will pick up the sound" rather than "the microphone doesn't pick up any sound".
We could argue that the microphone only picks up pressure waves and that sound doesn't exist until our ears play back the recording, but this isn't what people mean. If someone said "the microphone didn't pick up any sound" we would interpret that to mean the microphone wasn't working, or the firework didn't go off i.e. we are assuming the firework's explosion causes the sound. Instinctively, we tend to assume that sound is coming from the object in the room, not the detecting equipment.
We don't refer to our ears "creating sound" we refer to them "hearing a sound". I therefore suggest that the way people tend to use the word "sound", means the actual pressure wave moving through the air.
So, the tree will fall under gravity, causing the air particles to move out of the way. If we accept that the tree and the air will behave under normal laws of nature then the answer to the question is : Yes, the tree does make a sound.
The philosopher George Berkley spent a lot of time writing on this very topic and even talked about the fact that trees may not exist when not percieved, which prompted the revered Ronald Knox to write a rather nifty limmerick. A nice note to end on perhaps:
There was a young man who said, "God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there's no one about in the Quad."
Your astonishment's odd:
I am always about in the Quad.
And that's why the tree
Will continue to be,
Since observed by
The moon is usually the same average distance from us (about 380,000 km) and while this distance can vary over the course of a year or a decade, the change in moon's size isn't easily detectable. The moon's orbit is elliptical, so at certain times it is closer and will appear bigger, but Sam is referring to the fact that the moon can appear different sizes on the same night, particularly when it's lower down in the sky. It's called "The Moon Illusion" and a huge number of Scientists have written about it including Aristotle, Thomas Young and Ibn Al Haytham (the co-inventor of Science itself).
The first thing to rule out is optical phenomena. If you compare photographs of the moon at different points in the sky, you can show that the moon's size is always the same in the camera lens. There is no distortion of light caused by the atmosphere. This means the effect is taking place inside our brains, rather than in the actual sky itself. It's an optical illusion and straight away that means things will get foggy.
The cause for this illusion is difficult to pin down, but the same is true for all illusions. Because we still have no idea how the brain percieves reality and how vision works, any question about perception will always come with a bit of hand-wavy ifs and maybes. The short version is that really bad at judging the world and analysing it. That's one of the reasons we invented Science, to get around the fact that our senses basically suck.
For some reason, when we look at the moon near the horizon we mistake it for bigger. The explanation may be something along the following lines: we see it in the sky on its own and get a sense of how big it is. When we see it near the horizon we expect it to appear smaller by comparison. Yet, it refuses to be any smaller. Our brain is confused: the moon is now next to an enormous horizon, so it should appear less significant, yet it doesn't. Ah, says the brain, I know what's going on - the moon must be bigger! And thus our brain sees the moon as it really is but convinces our conscious interpretation that it has somehow swelled in size. Moral of the story: your brain is not always your ally.
Lewis explains in his question that he was filming something with a camera while standing beneath some powerlines but when he watched the footage back, it was humming. How does this work? The answer is something called electromagnetic induction and it was discovered by Michael Faraday (the man who used to be on the £5 note).
The first thing to do is get our heads round a very unusual idea called the electromagnetic field. Imagine a fish sitting inside a lake. In every direction the fish is surrounded by water, but the fish is probably unaware of it. But if something moves through the water, it will create ripples which the fish will be able to feel. In this way, it's possible to send a signal through the water by disturbing it slightly.
Even though it sounds like made up mumbo-jumo, our Universe appears to be filled up with a similar type of fluid. In every direction we are surrounded by an invisible force-field which goes on forever. We call this invisible substance the electromagnetic field. Whether it's made of anything or whether it's fundamentally pure, we have no idea. But it's everywhere and certain things can interact with it, creating ripples and bends in the field. A magnet, for instance, distorts the shape of the field so that certain metals will be twisted and pulled in along with it, following what are called the "field lines".
One of the particles which seems to interact particularly well with the EM field is an electron. As an electron moves around in the Universe, it creates ripples in the electromagnetic field as it goes. They're usually quite faint, but if we get enough electrons all moving in the same way, we can create an enormous electromagnetic ripple which travels through the Universe and can be detected by distant electrons. I know a lot of this sounds like nonsense, but this really is hard Science.
Now let's talk about powerlines. Electricity is usually the movement of electrons through a substance (there are some exceptions but this covers 95% of cases). As electrons stream down a powerline they create an electromagnetic "wake" behind them, the same way a speedboat creates a wake on the surface of an otherwise sleepy lake. This, on its own, doesn't do anything exciting, but if you get the electrons to zip back and forth inside the wire it creates waves in the EM field - waves which travel.
Electricity in a UK powerline is made up from trillions upon trillions of electrons hopping backwards and forwards at 50 Hertz (50 times per second). This means the electrical current in a powerline is generating EM waves 50 times a second.
Inside all electronic equipment there are more electrons zipping around inside its circuitry. For the most part they stay on course, but if a big enough EM wave approaches, the electrons inside the device will start to oscillate as well. This means that anythinig which is recording the world will pick up these 50 Hz EM waves. Having the camera near a powerline is doing exactly that.
The electrons in the powerline are zipping back and forth, this creates EM waves which radiate out from the cables. The waves reach your camera and cause a faint waggling back and forth of the electrons inside, causing a faint buzz or hum. The magic of Electromagnetic induction!
The human brain is the most complicated structure on Earth. 86 billion electrically conducting cells all linked up in a chemical network with up to 100 trillion connections. So, as with all brain-related questions, the answer to "what causes X" is still a mystery. Particularly when it comes to emotions and feelings.
What we do know is that certain mental activities seem to take place in certain brain regions. What I mean by that is that when we monitor a human brain experiencing a particular emotion or undergoing a particular task, we can monitor how much electrical activity is taking place in the brain and we discover that certain regions match certain thought processes.
The chemicals which move in between the brain cells (telling them to conduct or not) are called neurotransmitters and they also play a significant role of some sort. Oxytocin, for instance, is a neurotransmitter which gets released/manufactured a lot when a person is in love. We don't know what the cause-effect relationship is though. Does seeing a person we fancy trigger an oxytocin release in the brain? Or does oxytocin get released in the brain at random, telling us that we fancy a certain person?
To make things more confusing there are only a few dozen neurotransmitters which get used but obviously there are way more emotional states or thought processes available to us. What do we make of that "Sunday afternoon feeling" or "the feeling of being jealous of our best friend" etc. etc.
In short, we don't know how thinking works and how emotions are processed. What we do know is that when these chemicals get imbalanced in the brain it can cause psychiatric illness and that, for some people at least, taking medications to restore the correct ratios of these neurotransmitters can restore the person's mental health.
Anxiety seems to be associated with an imbalance of four chemicals in particular: serotonin, dopamine (two neurotransmitters) cortisol and adrenaline (two hormones). Cortisol is the "stress" hormone, a chemical in the blood which rises when you're doing tasks your body isn't built to take for too long, it's like a warning system for your organs to slow down.
Adrenaline is the "fight/flight/play dead" hormone that gets you ready for challenge. Serotonin is the "happiness" neurotransmitter which gets produced when you are experiencing contented happiness. Dopamine is the "energetic bring on the world" neurotransmitter which generates feelings of excited confidence and thrill.
Serotonin is more the "relaxing comfortably on a beach chair" neurotransmitter while dopamine is the "at a gig rocking out to music" neurotransmitter. Although obviously the two are closely linked and they can impact each other's production/release.
The brain regions most involved in anxiety seem to be the amygdala and hippocampus - the brain's emotional centres. As I said earlier though, at the deepest level nobody knows how thought works so nobody really knows WHY serotonin is associated with happiness. We don't know whether being happy causes serotonin to be released leading you to act/think a certain way or whether serotonin release triggers "happiness emotions". The ins and outs are insanely complicated but the approximate gist seems to be something along the following lines:
If serotonin get too low the person suffers depression, obsessive compulsive disorder or eating disorders.
If dopamine gets too high the person suffers psychosis/delusions and possibly schizotypal symptoms.
If cortisol gets too high the person suffers from stress.
If adrenaline gets too high a lot of different things can happen ranging from heightened bloodpressure to an unusual condition where your skin changes colour.
Anxiety seems to be a combined imbalance of these four chemicals. If the serotonin gets too low, but the dopamine and cortisol get high at the same time with a little bit of adrenaline, the result is anxiety, sometimes mixed with depression. Sometimes this can be triggered by certain things (phobias), sometimes they are at a constantly mis-matched level (anxious personality) and sometimes they just go haywire (panic attacks).
Panic attacks are rather unfortunately named because they often have nothing to do with panicking. A person can be sitting on a hillside looking at an apple tree and suddenly get a crushing pain in the chest, hyperventilation, dizziness, vomiting, crying, hot and cold flushes and headaches all out of nowhere.
For sufferers of "panic attacks" it feels as though they are about to die, which is what the body thinks is about to happen. You get the same kinds of effects on the body and brain that a person would experience being locked in a room with a tiger. It's not the person worrying about something, it appears to be a biochemical illness they have little conscious control over. Granted, the overall cause can sometimes be stress, but people who suffer these attacks don't need to be told "calm down" because they physically aren't capable of it.
The good news is that panic attacks, while indescribably horrible, pose no actual danger to the victim. It's sort of like your body's burglar alarm system going off by accident. All the symptoms and warning signs are there, but the person is completely safe.
As to curing anxiety and panic attacks, the answer is that different things seem to work for different people. For some people medication is the answer, for others it's meditation. For some psychotherapy helps, for others it could be a change of job. So the short answer is that as yet, we only have a half-answer. But the same is true for pretty much any emotion or feeling. The brain is just too darn complex.
Our solar system doesn't have just one asteroid belt, but two. The one orbiting between Mars and Jupiter is either called "The Main Belt" or occasionally "The Asteroid Belt". The second one lies out past Neptune and is called the Kuiper belt (pronounced Kie-pur) named after Gerard Kuiper, one of the pioneering planetary Scientists of the last century. Lewis' question is what kinds of element you'll find out in the Kuiper belt. It's a great question and I can only give a half-answer. So, first let's make sure we're clear on what elements are.
Everything in the Universe is made from a very small recipe of particles. The same particles, rearranged in different forms, gives us everything we can see. These particles don't exist on their own however, they tend to clump together in stable structures we call atoms. Every atom has a number of particles at its centre called "protons" and the number of protons at the centre of the atom determines what type of atom it is. One proton at the centre is called Hydrogen, for instance. Two protons is called Helium, three is Lithium and so on. Each of these different atom types is called an element.
At the moment there are 118 named elements (118 different types of atom) ranging from 1 proton at the core to 118 protons at the core. 91 of these atom-types occur naturally while the other 27 have to be made artificially and only exist for very brief amounts of time.
As far as we can tell, nature only makes atoms with whole numbers of protons. One proton, two protons, three protons etc. Nature doesn't make fractional-protons very easily (NB: there are unusual and exotic states of matter which could theoretically be made which would fit in between the 118 normal elements, but these haven't been made yet).
What this means is that the 91 occuring elements on Earth are quite likely to be the same 91 occuring elements throughout the Universe because element 1.5 doesn't easily exist. What does change are the abundances. Planet Earth is very rich in Iron and Nickel for instance, while Jupiter seems to be very rich in Hydrogen.
So Lewis' question about the amounts of the different elements is really asking how much of each element type we'd find out in the Kuiper belt. And the answer, for now, is that we don't know. We've only ever sent five probes out to that distance and none of them did any landings or drillings, and none of them were return journeys, so we don't yet know what the rocks out there are like.
We know a little about the gases floating in between the rocks however because gases interact with light in specific ways. We can observe the way the Kuiper belt's gases distort the light of distant stars and that tells us what types of atom we have in the gas (so far a lot of Nitrogen, Hydrogen, Oxygen and Carbon) - very similar to the surface of the Earth in fact.
As to the rocks themselves, we can only make educated guesses. Most of the rocks we've discovered in the solar system are generally based on the elements silicon, carbon, oxygen and various metals, so if I had to place a bet I'd say Kuiper objects are probably the same, but for now we don't really know.
When you read a standard Physics textbook it will usually give the speed of sound as being roughly 330-340 m/s, depending on the book. When books quote this value they aren't actually quoting a constant, they're telling us the speed of sound specifically at sea level and at 15 degrees celsius (the average air temperature over land). But at -50 degrees (the temperature in certain parts of Antarctica) the speed of sound can drop to below 290 m/s. And at higher temperatures, 50 degrees say, it can speed up to over 360 m/s. In other words, sound will travel faster in hotter air than in colder air. What's going on?
Sound is the result of air particles being spread out from a vibrating object (a voicebox, a ruler twanging on a desk) and then crashing into a bunch of nearby paticles. As they crash into this nearby bunch, all the particles are momentarily squashed together, creating a dense spherical shell around the source of the sound. But then, the particles rebound from each other and we end up with the exact opposite, a shell of really sparse air with not many particles in it. This bouncing-off-each-other effect then gets repeated as the particles are sprayed out further, bumping into a new shell of air particles and so on.
The result is that we get a sphere of compressions spreading out from the surface of the vibration, and then a smaller sphere of rarefactions (spread-out air), and then a smaller inner sphere of compressions, and then so on on. We end up with a sort of gobstopper structure of alternating compressed/expanded regions of air spreading out from a point. We call the outermost shell of this soundwave a wavefront. When the wavefront hits your ear, the eardrum is pushed back and forth as the soundwave repeatedly crashes into it, sending electrical signals to the brain which we interpret as sound.
Lots of things can affect how fast this wave of air-ripples can travel but the main factors are: speed the particles are moving at, the density of the particles (how many there are in a given volume) and the pressure they are exerting on each other. There's a nifty equation which links them all, saying, roughly that the speed of a wave is calculated as the square root of the rate of change of pressure, per rate of change of density. What it means is that if the air is doing different things and has different densities, pressure and particle-speeds, we'll get a different soundwave speed.
The two main things which affect sound speed are altitude and temperature. Near the surface of the Earth, the air is quite thick because the particles are all pulled together under gravity, giving us a speed of around 340 m/s. But about 10 km up, the air is a lot thinner, and so as particles are spread out from the vibration source they don't bump into each other as often, the compression doesn't immediately form, causing the bounce-back, so the overall speed of sound is a little slower (around 300 m/s).
The most confusing, and surprising, factor however is that sound travels faster in hotter air. Your instincts would say that it should go slower, since hotter air is less dense (and we've just learnt that less density usually means slower speed), but it turns out particle speed has more of an effect on overall wavefront speed. Hotter air is full of particles that move faster, and so they are quicker to "rush in to fill the gaps" in a progressing wavefront. It's actually as simple as: faster air = faster vibrations.
So the speed of sound is hardly constant at all. Sound will travel differently on different days and at different altitudes. They all cluster around a similar-ish mean value (300 m/s) because the density of a gas hovers around a specific value on Earth, and particle impact energies all have a definite constant force associated with them, but the speed of sound can fluctuate with the weather.
The speed of light is much the same, having a constant value only in a vacuum but being slower in certain mediums like glass and water. The only thing known to travel faster than the speed of light is the speed of rock and roll.