Getting Lost With Einstein's GPS - EWTS #006

Joe: Welcome to Enough with the Science and basically what we're doing here is we're talking about science. And, um, Senan is a bit of a science nut, and I'm not. So he understands things that maybe most people shouldn't. And he tries to explain them and I ask him questions to try and put him off essentially.

Senan: Joe challenges me to put everything into words of one syllable.

Joe: Even I can understand them, sometimes. So this is actually part two. This is our first part two of a part... two-parter? Honestly?

Senan: Yeah. So last week we gave an introduction to the electromagnetic spectrum or electromagnetic radiation or light as a lot of people call it. And this week we're going to continue on that theme and finish off that whole electromagnetic spectrum stuff.

Joe: Finish off the electromagnetic spectrum.

Senan: Absolutely. We've had enough of it.

Joe: Well, yeah. The universe will just have to limp along on its own without it. I imagine listeners might have had enough after the first episode, but we shall see. That remains to be seen.

Senan: Let's just do a quick recap of what we spoke about last week.

Joe: Okay, don't ask me any questions.

Senan: So, anyway, we found out that electromagnetic radiation, it's all radio waves, light, X-rays, gamma rays. It's all made of the same stuff. It's all EM radiation. And this EM radiation is emitted when charged particles change speed or when they change direction.

Joe: It's coming back to me. Yes.

Senan: That's how it's born. And one of the weird bits, of course, is that it's not one wave like we see when you look at the beach. It's two waves together at right angles to each other. You've got an electrical wave and a magnetic wave traveling together. Did you recall that bit?

Joe: No. Well, there was something about a cross. I remember there was a cross going through the universe.

Senan: Yeah, yeah, that was the cross. So now we really delve into the weirdness. We discovered that it is both a wave and a particle at the same time.

Joe: Oh yeah. I remember this now. This is where it started to hurt.

Senan: So the particle is called a photon. You'll be hearing a lot about photons today. And it's really one of the most difficult aspects of electromagnetic radiation to understand is the fact that it behaves both as a wave and as a particle at the same time, and that has been proven with different scientific experiments.

Joe: Maybe the experiments are wrong. Maybe there should be a third thing. Maybe it's not a wave or a particle, it's something else. A warticle. Or a pave.

Senan: You know, you could well have come up with the perfect encapsulated description of it there. A warticle.

Joe: A warticle park.

Senan: Moving quickly along before we get kicked out of the Academy of Science again. There's a couple of interesting measurements about EM radiation. I'm going to call it EM radiation from now on because calling it electromagnetic radiation is sooner or later going to...

Joe: I bet you don't. I bet you say electromagnetic radiation again at some point.

Senan: I'll do me best.

Joe: EMR.

Senan: Anyway, so there's a couple of measurements that are important. Frequency is one. That is how many waves every second. So if you were standing still and you were watching the waves going past you and you counted them, it's how many of them pass you in a second. That's how frequent the waves are or the frequency. And the other important measurement is wavelength, which is the length of one wave from a peak to a trough... a peak to a peak or a trough to a trough. Now, just one important point to note about that. The higher the frequency of the wave, the more energy is in each photon. And that's the difference between all these different kinds of radiation, be they radio waves, light waves, X-rays, gamma rays, etc. It's the amount of energy that the photons carry and the frequency which the two things are related. The higher frequency, the more energy.

Joe: So the more waves that pass a certain point per second, the higher the energy?

Senan: Correct. The photons that are part of that system have higher energy, yeah. So each photon is kind of like a packet, a discrete packet of energy. So you can't kind of have a half a photon. You either have the full photon or no photon at all.

Joe: But the photon is part of the wave?

Senan: Oh, we're not going back over this again.

Joe: Can we not just... well, I give up. Okay. There's photons in the waves as part of the waves and they are the waves and they're all the same thing.

Senan: That's it, yeah. That's it.

Joe: There we go. Okay. So all of these... this EMR... see what I did there? EMR.

Senan: Oh, EMR. Good, yes, yes. Let's save energy.

Joe: The podcast will be over in about ten minutes if we keep abbreviating everything down to...

Senan: Electromagnetic radiation.

Joe: So all of this electromagnetic radiation is flowing in all directions at the same time?

Senan: Uh, what do you mean by that now?

Joe: Well, so it's not... we established last week, it's not like a wave on the sea that's flowing one way just on a one plane. It's on all the planes.

Senan: Oh, so you're talking about if there's like a light bulb turned on.

Joe: Oh yeah.

Senan: And light appears to go in every direction from it. So there's waves going away from it in every direction. It's a bit like if you... it's a three-dimensional version of what happens in the sea, which is kind of two dimensions. If you throw a big stone into the sea and suddenly you see waves spreading out in circles away from where the stone went into the water. So it's a bit like that. The waves are spreading out in all directions but they're kind of... you can think of them as individual waves, one going left, one going right, etc. One going up, one going down.

Joe: And these are everywhere?

Senan: Well, they like... we can see anywhere you can see light, there's light waves traveling around.

Joe: Okay. But like even as we said last week in deep space there's...

Senan: Oh yeah. There is certainly microwave radiation and infrared radiation and light all over the place in space, yeah. And all of it of course has a speed limit.

Joe: Someone always wants to break up the fun. Don't they? Wants to stop. You're going too fast. Slow down.

Senan: Well unlike the speed limits that are on the signposts at the side of the road here, you can't actually go any faster than this speed limit. Nobody can. Nothing can. So it's not like a suggestion that we have in the bylaws.

Joe: This is the limit of...

Senan: This is the universal limit.

Joe: It's actually like it is the limit of speed itself. It's not just a speed limit, it's the speed limit.

Senan: It is the speed limit of everything. Yeah. And it's a huge number. It's about... slightly above a billion kilometers per hour. Now, I don't know about you, but I can't visualize in my head what a billion kilometers an hour are. So let's take that down to something that's a little bit more understandable. 300,000 kilometers per second. Does that help you?

Joe: No.

Senan: Okay. Right. We're going to go even lower. Seven times around the Earth in one second.

Joe: Okay. Superman speed.

Senan: That's how fast light can travel in a vacuum. Now, in other... so light traveling through water, for example, travels at a slightly different, slower speed. But light in a vacuum is the actual speed of light and it's seven times around the Earth in one second. And it's the ultimate speed limit for everything. And why is that? It's baked into Einstein's theory of Special Relativity which he developed about a hundred years ago.

Joe: Oh, here we go. Big words again now. Monosyllables we said.

Senan: So Einstein came up with these two theories, General Relativity and Special Relativity. And they have held true. Despite, you know, a hundred years later and a lot more sophisticated experiments being done by scientists and a lot more sophisticated calculations on computers and so on, Einstein's theories hold up. It's incredible. The mathematics that he did back then is still fundamentally correct as far as we know.

Joe: So no experiments have contradicted his view?

Senan: Not in any substantial way. There might be little threads being pulled at the edges here and there, but not the substantial underlying stuff is still correct.

Joe: Brainy lad. Brainy lad he was.

Senan: Unbelievable. They broke the mold when they made him. Anyway, so his theory of Special Relativity... the mathematics that he developed tells us that as something with mass gets faster... so what do we mean by something with mass? Well, you can think of it as something that's heavy. So mass and weight are not exactly the same thing but here on Earth where there's gravity, we can treat them as if they're the same thing. So if you pick up something that you can feel weight in your hand, that's the mass of it that you're feeling. So his theory says that if something that has mass speeds up, its relativistic mass increases. What does that mean? It means that it doesn't actually get heavier, but it behaves as if it's getting heavier. Right?

Joe: And there's a difference?

Senan: Who knows?

Joe: It behaves like it's heavier... so if you weighed it, it behaves like it's heavier. So it is heavier.

Senan: Yeah, look... I think for ordinary mortals like us it means the same thing.

Joe: Okay. I think we can just accept that if we don't have the instruments to separate behavior from actuality...

Senan: Yeah.

Joe: ...then we just treat it as actuality.

Senan: Anyway. One of the implications of that, of it appearing to get heavier, is that you need more and more energy to make it go faster. You know, a heavier thing needs to be pushed harder than a light thing to speed it up. Right?

Joe: Okay.

Senan: So this thing is behaving like it's getting heavier and heavier the faster it goes. So you need more and more and more and more energy to make it go faster and faster. And if you follow Einstein's equations, you come to a point where it says to increase its speed to the speed of light would require infinite energy. Which is a nonsense. There's no such thing as infinite energy. So what it means is that nothing that has mass can be accelerated to the speed of light.

Joe: And so speed of light is the limit. There's obviously several points before that where it becomes almost impossible.

Senan: Awfully hard to do it. Yeah. Awfully hard to do it, yeah. Now we're talking about massive speeds. So anything that we have accelerated as humans is crawling slower than a snail. We're not getting into this problem about needing more and more energy to push things faster doesn't affect us because we haven't made anything go fast enough to do it.

Joe: What about those things that they're shooting around the tube in CERN? They're pretty quick, aren't they?

Senan: Yeah, yeah, they're pretty quick but they're, of course, tiny, tiny amounts of mass.

Joe: Yes.

Senan: So the amount of energy required to accelerate them is relatively small. But still, the faster they make them go, the more energy they need to make them accelerate, yeah. So, however, now let's talk about why does light travel at the speed of light or EM radiation really travel at the speed of light? And it's because the photons have no mass. They have no weight. The photons that light is made from have no mass. They're effectively... if something has no mass but exists, it's pure energy. So they are packets of pure energy and they are born traveling at the speed of light. They don't accelerate from zero to the speed of light, they are born traveling at the speed of light and they never come below that speed.

Joe: Until they... do they die? Traveling?

Senan: Until, for example, your eye sees light coming from a light bulb. The photons that have gone into your eye have reacted with the cells in your eye and been absorbed. That's how you got to see that light.

Joe: Okay, so they're gone. They're not passing through you.

Senan: Oh no, no, they're gone. Now if they were X-rays, they'd be passing through you alright.

Joe: Obviously.

Senan: No, but the light doesn't. So yeah, it's all a consequence of the mathematics that Einstein worked out that we know all this stuff. And I mean...

Joe: So if you turn on a light, right?

Senan: Yeah.

Joe: And you're 300,000 miles away. Kilometers away.

Senan: Yeah.

Joe: You would see the light in one second.

Senan: Yes.

Joe: If the light was strong enough.

Senan: Yeah.

Joe: But there would still be photons even if you couldn't pick it up probably.

Senan: Oh yeah. I mean if you had a sensitive... oh yeah, some photons would reach there. Assuming nothing got in the way that stopped them in the meantime.

Joe: Yeah.

Senan: So the sun, right, is eight light minutes away from Earth.

Joe: Mm-hmm.

Senan: So if the sun was to suddenly get extinguished, we wouldn't find out for eight minutes. It would look exactly the same until all the old light from before it got extinguished had passed us by.

Joe: So like as part of a philosophical discussion, we can only see the past.

Senan: Correct. Yeah. Even the fact that you and I are sitting a meter apart, what I'm seeing of you is the past.

Joe: Yeah.

Senan: You could be dead now for all I know.

Joe: I could be. Milliseconds ago I could have just had enough of this and just throwed myself against something sharp.

Senan: Ah no, no. It's not that bad. Use something blunt. It'd be easier. Anyway, back to the...

Joe: Oh yes, back to the EMR.

Senan: So here's an interesting conundrum for you. So you're driving down the motorway at nighttime in your car. You're doing 700 miles an hour.

Joe: As usual.

Senan: And you push the button on the dashboard to switch on the lights. So the light that's leaving your car at the front, you would imagine is traveling at the speed of light plus the 700 miles that you were doing already. That's what you would intuitively think is happening.

Joe: Mm-hmm.

Senan: That's not happening because it's stuck at the speed of light. So what actually happens is that time is slowing down slightly for you because you're traveling. And that means that the speed of light... the combination of the speed of your vehicle and the speed of light being emanated still doesn't exceed the actual speed limit. So the faster you travel, the more time slows down for you. And that's another one of those really mind-bending things.

Joe: See, we should do a whole episode just on that. That alone is just big enough that the faster you travel, the slower time goes.

Senan: Yeah, yeah. And do you know one of the most commonplace, a thing we use every day that's affected by that is GPS. So GPS satellites are traveling quite quickly. I mean they're not traveling at 300,000 kilometers a second, but they're traveling quite quickly. Several thousand kilometers an hour. And GPS accuracy relies on extremely accurate atomic clocks that are in those satellites.

Joe: Right.

Senan: So the satellites are transmitting a time code and that's how your phone figures out where you are. That's how it works out position. But they discovered after they set up the GPS system that it was inaccurate. And the reason it was inaccurate was because the time on the satellites was moving slower than the time here on Earth. Because they're moving faster than us.

Joe: Right. Okay.

Senan: So they're going fast enough for us to see the effect. So they have to literally manually tweak the clocks on the GPS satellites to go, run slightly fast to compensate for the fact that time on those satellites is running slowly.

Joe: So even on a plane?

Senan: Yeah. Now the speed a plane is traveling at is very... the difference is tiny. But they have taken... there has been an experiment done where two atomic clocks that were set synchronized to the exact time, one of them was put on a plane, flown around the world a couple of times and then they took it off the plane and sure enough, yeah, it had slowed down.

Joe: Yeah. It's mind-bending stuff.

Senan: So if you want time to speed up we just have to stay still.

Joe: Yeah. I mean there's a well-known trope in science fiction novels that a character maybe their long lost love is going to be years before they'll come back to see them again, and they don't want to be an old person when that long lost love comes back. So they go onto a spaceship and start traveling around really, really fast to slow down their aging. So that when their lover comes back they won't be too old.

Joe: Oh my god. I hadn't even thought of that. So like if you're on a really, really fast spaceship, your aging process slows down?

Senan: Yes. Yeah.

Joe: So this is why they're investing millions in private space companies. I can see it now. I can see it. They wouldn't do it for the good of mankind.

Senan: Let's say we were able to build a spaceship that was able to go at, you know, 30, 40% of the speed of light and we sent it off to some star that's 20 light years away or something. So that astronauts could explore that star. And then they come back again in the same spaceship. So that's 20 light years each way. By the time they get back, the people that they knew on Earth would be a lot older than they expect them to be. Some of them might even be dead from old age.

Joe: Yeah.

Senan: You know. So it's a weird... it's a weird thing.

Joe: Yeah. I've seen a couple of movies. Interstellar melted my head when they were trying to explain that whole concept of people being at different places.

Senan: Yeah, yeah. My favorite line in that movie: "Those aren't mountains." Do you remember that?

Joe: No.

Senan: They landed on some water planet.

Joe: Oh, they were waves.

Senan: They were massive tidal waves. Yeah.

Joe: Ah yes. Yes. It's coming back to me.

Senan: Anyway. Back to the...

Joe: Oh yes. Back to the EMR.

Senan: We're going to tour through the various types of EM radiation.

Joe: The locale. Here on the left...

Senan: So we're going to start at the low energy end and that's of course radio waves.

Joe: No reflection on this podcast.

Senan: No, well... this is the modern world and it's all going to be in ones and zeros on the internet.

Joe: We're still wireless. This is still wireless production.

Senan: So, um, we're talking about long wavelengths here. So anything from millimeters up to kilometers in fact. So some radio waves are kilometers in length. FM radio that, you know, people listen to music on, wavelength there is about three meters. AM radio which is an older fashioned and I think is used mainly for talk radio in the US and it's hardly used here in this part of the world anymore, wavelength there is about 100 meters.

Joe: And does that mean that if you wanted to broadcast to further away, it would be better to use AM?

Senan: Um, yeah, but not probably for the reason you're thinking of.

Joe: Ah. Okay. No, I'm right. Just let me be right. You don't have to correct me. Just say "you're right."

Senan: Yes, yes. You are right. You are right. I'm not going to question your thought process. You are right.

Joe: Okay. Just let me... yeah. Don't explain how I'm wrong.

Senan: It's an interesting point. Longer wavelengths are able to diffract or bend around obstacles.

Joe: Ah.

Senan: And they're also able to bounce off the ionosphere which is a layer high in the atmosphere. So that's why some of those... like if you consider some... a lot of EM radiation is pure line of sight. So for example if I shine a torch, there's a shadow caused by something in the way of the torch because the light is going in straight lines and it doesn't go around the back of where the shadow is, if you know what I mean.

Joe: Yeah.

Senan: So the... that means that using radio waves for communications, if you don't have line of sight... so you're trying to communicate with somebody who is halfway... say a quarter of the way around the planet.

Joe: Yeah.

Senan: You know, so the curvature of the Earth is in the way. You can't actually go fly a straight line to them. You'd have to go through the Earth to get to them. So these long wavelength radio waves, they can bounce off the ionosphere and effectively bounce around the curvature of the Earth and go much longer distances.

Joe: Ah. Okay.

Senan: So that's kind of why it's handy for that.

Joe: You know all those movies from the 1970s where everybody seemed to have a Trans Am car and a radio? Like kind of a CB thing. Were they AM?

Senan: Um, I don't know. I think the CBs in this part of the world were FM band but I could be... I can't remember. I did... there was friends of mine who experimented with that stuff.

Joe: It's a Breaker 1-9. Breaker 1-9. There's a Bear in the hardware.

Senan: All that malarkey and movies with...

Joe: Smokey and the Bandit.

Senan: Yeah, that was the one. That was the one. So another reason that radio waves are good for communication is they penetrate through walls and wood and stuff easily. And that's because the energy in the photons that these long wavelengths have is low energy and it's too low to interact with the atoms in the walls. So higher energy photons would be at the right level of energy to actually be absorbed, for example, by the walls or the timber or whatever. So that's another reason why radio is good. Obviously there's AM, FM radio. There's television signals, Wi-Fi, Bluetooth, GPS, radar for finding planes and ships in the distance. All of that is using radio waves. Now there's an interesting question. How do we make those radio waves carry our voice?

Joe: And the information in them.

Senan: Yeah, yeah.

Joe: I ask them nicely. Send them a strongly worded letter.

Senan: So the audio that's coming out of my mouth right now is setting up waves in the air. We can't see them but there are compression waves in the air being caused by my voice. And there's a particular pattern of waves traveling through the air. So we can take that pattern and superimpose it onto the radio waves.

Joe: Okay.

Senan: So that's essentially how we're making the radio waves carry the information for us. It's a process known as modulation. So what you're just doing is taking the pattern of my speech and superimposing it onto... modifying the radio wave waves to take that pattern with it.

Joe: It's not only speech, like it's everything that is audible?

Senan: Everything that's audible, but also even even ones and zeros of data, we can modulate that. And there's kind of two main schemes for doing that. One is called Amplitude Modulation which is AM radio that we mentioned earlier on. So what that does is it varies the height of the waves a little bit. That's how it imposes the pattern, by making small changes to the height. And the other kind, FM radio, Frequency Modulation, it changes the frequency of the waves continuously just by slight amounts. So that's how the pattern gets encoded onto the radio waves. It's interesting stuff.

Joe: It just blows my mind. Marconi, was it?

Senan: Yeah, that he figured out all this stuff.

Joe: But did he figure that out or was it sort of a practical thing he kind of went, "Okay, I connect up these two things and you can hear it over there and okay, then we make a bigger cable and we move that over here and suddenly like..." Or was he actually sitting down going, "Yes, I think I'll change the amplitude... do the frequency of these particular waves..."?

Senan: Yeah. I wonder how much he understood about it. I don't know.

Joe: That's another show. I'm writing that down.

Senan: So what happens then is how does the receiving radio at the other end pick up the signals? So it's got an antenna. And the waves passing by that antenna make the electrons that are in the metal of the antenna wiggle up and down to match the movement of the radio waves as they pass by the antenna. And then there's an amplifier. So that creates a wiggling current if you like in the antenna. And there's an amplifier in the radio receiver that picks up that tiny current and amplifies it, makes it bigger until we can hear it.

Joe: And that picks it up at a specific frequency?

Senan: Yeah, the electronics are able to tune into the correct frequency, yeah. But also there's different frequencies use antennas that are of slightly different length. So the antenna has to be a multiple of the wavelength or the wave height... you have me there now, I can't remember.

Joe: Okay. That's where you failed. Sorry. Next.

Senan: The point is that the antenna has to be more or less matched to a set fraction of the actual wavelength or the wave height. Microwaves. Moving slightly up the spectrum.

Joe: Okay. So we are basically increasing the frequency as we go, isn't it? Increasing frequency and energy.

Senan: We're increasing the frequency and reducing the wavelength.

Joe: Okay.

Senan: So as frequency goes up, wavelength comes down. So microwaves, we're in the range of from millimeters up to about 30 centimeters. So that's like from millimeters up to about one foot in old money. It's the perfect frequency or at least one particular type of microwave is the perfect frequency for heating food. That's 2.45 Gigahertz. That's what your microwave oven is using. So what does that mean, 2.45 Gigahertz? So one Gigahertz is one thousand waves per second, frequency. Right? So almost two and a half thousand waves per second is what your microwave oven is producing. And that is energetic... the photons at that particular frequency are energetic enough to make the water molecules wiggle around violently so that the friction in the water molecules heats them up. That's what's going on there. And also it's got a reasonably long wavelength. It's 12 centimeters. That's long enough to penetrate deep into the food.

Joe: So all a microwave is doing, a microwave oven is doing, is boiling the water inside the food.

Senan: Oh yeah, just heating up the water in the food or it might also have the same effect on fat molecules.

Joe: Okay.

Senan: But it's essentially making them wiggle violently in tune with the speed of the waves that are passing through it. And that wiggling causes friction in the food that heats up the food.

Joe: Okay. So I mean it's not actually cooking the food, it's boiling the water which is then cooking the food.

Senan: Yeah, pretty much, yeah. Yeah.

Joe: Wow. Every day is a school day. Every day is a school day.

Senan: Every day is a miracle as Caravan Palace say. That's a band you probably never heard of that I like.

Joe: Yeah. Well, I've only heard of it because you like it so much.

Senan: We'll get them on the show.

Joe: My head...

Senan: Believe it or not, they do all their songs in English even though they're a French band so they could probably out-talk us as well. Anyway, back to the script.

Joe: Oh yes. Back to the EMR.

Senan: Microwaves are actually used also for some communication in the same way as radio waves. The reason is mainly that they carry a... because of the higher frequency, they're able to carry a very great density of signal. Squeeze a lot of information into a small amount of microwaves. So they're used, for example, say you make a phone call on your mobile phone. The signal initially goes probably over FM from your phone up to a nearby antenna on top of a hill somewhere. But that antenna then has to send on the call to some other place off in the... 50 miles away. And it typically will have a microwave dish on the antenna sending that signal and your call and hundreds of others that are going on at the same time all on that one microwave band to some other place.

Joe: Okay. So like the radio waves is kind of like a country road and the microwave is like a motorway.

Senan: Pretty much, yeah. Now we don't wholesale use microwaves for all communications because we don't want to be heating up everything around us unnecessarily.

Joe: I thought that might be... yeah. Or cooking ourselves.

Senan: Well it is used... there is microwave radar used for aircraft traffic control. It is used for some satellite communications out in space and some Wi-Fi bands do use microwaves but they're very low power so it's not enough power to actually cook us.

Joe: Thank God for that.

Joe: And some people misuse them by making their coffee in them.

Senan: And microwaves led to another fascinating discovery in astronomy. Something called the Cosmic Microwave Background.

Joe: And you're going to get back to space. I knew it was only a matter of time.

Senan: So scientists discovered that if they pointed a very sensitive microwave receiver at any place in space, any point of the sky, they could pick up these really weak microwave transmissions... microwave radiation. It was everywhere.

Joe: And somebody must have gone, "Aliens are cooking."

Senan: The aliens are heating up their curry. Yeah, if only that were true. And it could well be true in some places but it's not the cause of most of it. So it's actually the oldest light in the universe. It's leftover from the Big Bang. It was light that was produced 13.8 billion years ago during the Big Bang. And back then it was visible light. But the universe has been constantly expanding since the Big Bang and that has been stretching the wavelength. And it's now microwaves. So what was once visible light, by the expansion, stretching of the fabric of the universe which is still happening today, those wavelengths got stretched out until they were microwaves. And we see this real weak echo of the Big Bang everywhere we look.

Joe: And is it likely that if the universe keeps expanding as long as it's going to, that they will become radio waves?

Senan: Oh yes, yeah. Yeah. Now I...

Joe: Hooray! I'm following what's going on here. Hooray! I'm delighted with myself. I'm delighted. Look at that. I think we finished there. I never get things this right.

Senan: Yeah I tell you, your scorecard is going to be really good at the end of this episode. So yeah, it's interesting... the Cosmic Microwave Background is like everywhere. We'll move slightly up the EM band and come to Infrared. Which to you and me is heat. Essentially, you know, if there's a heater on in your room and you put your hand beside it and you can feel a warm glow on your hand, that's infrared radiation hitting your hand coming off the heater.

Joe: So all heat is infrared?

Senan: No. All heat is not infrared. The propagation of heat through space is infrared.

Joe: From the sun to here is infrared.

Senan: The heat element. But obviously there's also light, there's ultraviolet, etc. But there's another... just to briefly clarify the way you asked that question a minute ago. You know, a heater here on Earth where there's air around you in the room where the heater is on, heat is also being transmitted using something called convection where air around the heater is being heated up. It becomes a bit less dense than the other air that hasn't been heated up and it rises up. And you get this current of rising air being caused and that's another way of transferring heat. But out in space if your stove was lit out in space, if you could find the oxygen to support the combustion...

Joe: That's the worst analogy ever. If you light your stove in space and you can feel the heat even though you can't. But if you could, that would be infrared.

Senan: No, you will feel the infrared. The convection won't happen.

Joe: The convection won't happen.

Senan: That's the point I'm making. You'd only have the infrared then. So in terms of wavelength we're talking about between 700 nanometers... so nanometers are really, really small... and to around one millimeter. So the longest wavelength of infrared is around one millimeter. And literally everything you have ever touched is emitting infrared radiation. Like even you take a block of ice out of the fridge, that is believe it or not still emitting infrared radiation.

Joe: Liquid nitrogen.

Senan: Liquid nitrogen, yes. Anything that is warmer than absolute zero which is I think around about minus 270 Centigrade is emitting infrared radiation. And that's happening because the property of something being hot is down to the vibration of the molecules in it. So the hotter it is, the more those molecules are vibrating.

Joe: I think we'll use "dancing" from now on. Molecules are dancing. The more they dance, the hotter it gets.

Senan: So it's actually like we said, the thing that causes EM radiation to be born is charged particles changing direction or changing speed. So remember those molecules that are vibrating, they have electrons orbiting around them. So those electrons which are charged particles are going over and back, over and back, over and back. And that change of direction each time they wobble one way or the other is actually generating the infrared radiation. So yeah, it's interesting, infrared is everywhere around us. What do we use it for? Well, astronomy, there's a huge use in astronomy because the length of... well, I should talk about... we're all familiar with visible light and the spectrum, the seven colors of the rainbow.

Joe: Yes we are.

Joe: I think I can speak for all our listeners.

Senan: Well, yeah. So that piece of the electromagnetic spectrum is much shorter. The piece we can see is much shorter than the infrared piece. Another way of saying that is that in the infrared band there's a lot more colors than the seven we can see in the visible band. So if you use infrared... a camera, a telescope that can view infrared and you use it to explore the objects that are out in space, you'll see much richer pictures with more colors, more subtlety in them than you would with just visible light. So that's one reason why it's useful for astronomy. Another one is that there are in many parts of space there are dust clouds and gas clouds that visible light won't penetrate through but infrared will penetrate through. So it effectively allows us to see through some of those obstructions and see what's behind them.

Joe: But so the infrared camera is picking up infrared, but so that's essentially heat? Anything that is emitting heat?

Senan: Yeah, yeah.

Joe: Well heat is just another form of EM radiation like, you know?

Senan: So and then of course in order for us to be able to see those pictures, the computers that receive that data have to downshift it into the visible spectrum.

Joe: Right. Okay.

Senan: So the pictures you see published from the James Webb telescope, those have been shifted down by the computers into visible light so we can appreciate them cause we would not be able to see them with our own eyes otherwise.

Joe: And is infrared... it's like those cameras that pick up animals at nighttime. That's an infrared camera.

Senan: Yeah, yeah. That's picking up the body heat emitted by the animal.

Joe: A thermal camera. But is the thermal camera then shifting that down to be visible?

Senan: Yes, yeah. But what it's doing is... right, so remember the landscape around the animal is also emitting some heat. But what it's being very selective. It's saying heat below a certain level I'm going to treat as black and heat above that level, i.e. the heat coming out of the animal, I'm going to treat as brightness. So it's all about how the image gets processed by the computer that allows us to see it. So your remote control, certainly the older style of remote control anyway, uses infrared to... there's an infrared receiver in your TV and there's an emitter on the remote control. Even though you can't see it. But if you point your mobile phone camera at the emitter of a remote control you'll actually see the light then. Your mobile phone camera can see some infrared.

Joe: Oh. There you go. That's an experiment to do at home.

Senan: Yeah.

Joe: And I mean for me, maybe at home for you listeners as well, but I'm going to do that later.

Senan: So what else? Weather satellites use infrared cameras because they can see through the clouds. So, you know, satellites that we have up in space that are trying to predict weather patterns, they will use a mixture of infrared and visible light cause they see different things.

Joe: And assuming that infrared is benign to living stuff?

Senan: Well, it depends on how much of it you receive. I mean if you stand in a fire, obviously...

Joe: Yeah.

Senan: Yeah. So if you're standing beside a very strong infrared source, you know, your skin is going to burn or you're going to burn.

Joe: Not just your skin. You. Don't separate the two.

Senan: So it's a question of everything in moderation.

Joe: But the general background infrared that you're exposed to on a regular basis.

Senan: No, no. Nothing to worry about. So now I suppose we come to the one that we're all familiar with which is visible light. And it's only a tiny fraction of the full electromagnetic band, the full spectrum starting with radio waves and ending at the other end we'll talk about with gamma rays. The visible part that we see, it's less than one percent of the entire EM spectrum that our eyes can actually detect. In terms of wavelength you're talking about between 400 to 700 nanometers. Again very small, but smaller than the infrared we were talking about. In terms of how many waves would fit in one millimeter, about two million visible light waves would fit into a single millimeter. So they're very short wavelengths and they carry quite a lot of information. Now the interesting thing is why can we see that bit? Like, any ideas?

Joe: Well, evolution I would imagine.

Senan: A mixture of evolution and the particular kind of light that comes out of our nearby star which we call the sun. So different stars in... you look up in the night sky and you see stars all over the place. And different stars are emitting light or EM radiation we'll call it in different parts of the EM spectrum. But our particular star, the sun, the bulk of the light it emits is in what we call the visible part of the spectrum.

Joe: So are there stars that don't emit any visible light?

Senan: Neutron stars I think which are kind of the remnants of dead old stars. And then there are dim red ones... I should think of the names... there's a particular name for them...

Joe: Red giants, red dwarfs?

Senan: They could be red dwarfs or red giants, I'm not sure. But they emit very little visible light, it's a lot of it's down the infrared range. So yeah, there are different kinds of stars. And, you know, our star emits a certain amount of ultraviolet radiation but other stars might emit a hell of a lot more and so on. So it's likely or the scientists who are good at figuring out evolution think it's likely that vision first evolved underwater in creatures that were in the sea. And interestingly visible light is able to penetrate through seawater. So that was another reason why we can see that part.

Joe: Okay. So the other ultraviolet and those don't?

Senan: Yeah, they don't. Yeah, yeah. Or not very far, they might go like ultraviolet might go down into the water a centimeter or something and then be stopped, you know.

Joe: So I imagine if there was any sort of evolutionary advantage either now or in the future to being able to see ultraviolet or the other parts of the spectrum, then we will evolve to do that.

Senan: Yeah, so insects... there are some insects who can see some of the ultraviolet that we can't see. And there are patterns on the petals of some flowers that are only visible to creatures that can see ultraviolet because those patterns are effectively reflecting ultraviolet color rather than the visible color that we can see.

Joe: Oh yeah. What was that movie with the big tall blue people?

Senan: Avatar.

Joe: Avatar. That's it. Cause he lit a fire in the nighttime and she's going "What are you doing?" and she threw the thing away and suddenly the whole forest lit up. Like without the need for visible light, so...

Senan: Yeah. There you go. So plus something else is interesting, it has just the visible light has just the right amount of energy to excite certain electrons in pigment molecules and that enables the vision in our eyes. There's pigments in our... in the cones in our eyes that pick up that light that get... that react to the particular energy level that visible light has. And also photosynthesis. You know, where plants are able to take in sunlight, combine it with carbon dioxide from the air and produce structure. They basically take those two ingredients and build structure from it. Again it's all down to the fact that the light has the right amount of energy to interact with the chemicals in the plant. And we would not have oxygen to breathe were it not for that because the oxygen in our atmosphere has come about as a byproduct of the plants' photosynthesis.

Senan: It's a waste product basically. The oxygen that we breathe is something that the plants exhale. It's a byproduct of photosynthesis.

Joe: Plant poo. Plant excrement. That's what we are living on.

Joe: Yeah. But we wouldn't be able to do that if it wasn't for visible light.

Senan: Yeah.

Joe: But the plants wouldn't have evolved to use it.

Senan: Yes. Yeah maybe if we were getting bombarded with ultraviolet maybe they would have evolved to do triffids... the day of the triffids, giant plants would be our masters.

Joe: Yeah.

Senan: So chances are... as I mentioned earlier some insects can see ultraviolet. Chances are there are other animals who experience vision different from how we do because they can see slightly different range of colors or whatever.

Joe: Yeah. Never say never.

Senan: So that's visible. We'll move a little further up the energy spectrum and we'll go for Ultraviolet. So now you're talking about a wavelength of between 10 and 400 nanometers. Which to put that in a more understandable but not really understandable figure is five million waves per millimeter.

Joe: So the last one we were two thousand... were we? No the last one we were two million.

Senan: Last one was two million waves per millimeter. This is around five million waves per millimeter. So as I mentioned earlier it's present in sunlight. Some of it gets blocked by our atmosphere thankfully. Not all of it but some of it does. It's got enough energy... so because we're up to a higher frequency here, we are talking about more energetic photons. So the photons have now enough energy to excite electrons strongly. So when that ultraviolet light hits a substance, the electrons in that substance... depending on what that substance is made of... get affected, excited we'll call it, by that energy that's in those ultraviolet photons. And it can trigger chemical reactions in that thing that the light has hit. Or it can even break molecular bonds. So in other words break a molecule into its constituent elements. So that just the incoming energy... if you think of it like a very fast car crash, you know?

Joe: Okay. So remember that ad for Harp years ago? There was like Sally O'Brien was it? And the way she might look at you. And your man said you could fry an egg on the rocks out here if you had an egg. So was that infrared or ultraviolet?

Senan: Uh, oh not ultraviolet no. No. There's no heat. That would be the infrared element of the sunlight heating up the rock.

Joe: Okay. There we go. That's another mystery solved.

Senan: No, not ultraviolet, no. So the ultraviolet might have been weathering the surface of the rock. You know? It might have been chemically altering the molecules on the surface of the rock because its photons had so much energy that they're doing weird things to the electrons on the rock. We for our own convenience of classification we split the ultraviolet into three bands. So Band A or UV-A, that's the longest wavelength. It penetrates deeper than the other ones but... and it causes tanning and aging. But it's actually the least energetic of the UV. Then we've got UV-B. So that's what causes sunburn. So that's actually what damages our skin when we get sunburn. And it tans our skin without burning mostly. Now if you get a lot of UV-A you will get burnt by it but you're more likely to be burnt by the UV-B element because it's more energetic. Incidentally though it's also responsible for Vitamin D synthesis. So you know they say when you go outdoors in bright light, it helps your body to generate Vitamin D. It's the UV-B hitting your skin. So it's a double-edged sword. It's burning you but it's also generating the Vitamin D.

Joe: So we can't get rid of UV-B.

Senan: No. We just deal with the right amount. Moderation in all things. But it also can cause DNA damage because the energy of those electrons when it hits the DNA in your skin cells, it can actually mutate or damage the chemical structure of the DNA. So that's a potential for causing skin cancer.

Joe: Oh right. Okay.

Senan: So essentially your DNA is like your instructions to tell your cells how to grow, when to die, all the rest of it, what shape they should be. Suddenly the instructions get a bit scrambled and you get uncontrolled growth.

Joe: Or you're being very pessimistic though. Maybe they'd be scrambled into "You're going to live forever and be completely healthy."

Senan: Oh perhaps yeah, yeah. And there may be a few people like that living amongst us but they're very good at hiding. Anyway. And then Band C, the most energetic, UV-C. Definitely dangerous to life. Thankfully most of it is blocked by our ozone layer in the atmosphere other than where that hole is down near New Zealand. But it's used in... we can create lamps that create it artificially and that's used for germicidal lamps. Have you heard of those?

Joe: No. I think you're just making up words now. Germicidal.

Senan: So it can be used for example in water sterilization. So you can pass water which has bacteria or viruses in it through a bank of these UV-C lamps and those microorganisms can't cope with that and it kills them. So it's kind of a form of sterilizing things. So yeah that's ultraviolet. And it has all kinds of other... there's a lot of ultraviolet coming in from the sunlight and other bodies that don't have an atmosphere to protect them like the moon for example. The ultraviolet hits the surface of the moon and does all kinds of interesting things to the moon dust on the surface of the moon and other planets that don't have an atmosphere as well. So yeah we're lucky we have that atmosphere there to protect us. Even higher energy of course is something that most people are familiar with. X-rays. Because of hospital diagnosis.

Joe: Yeah. And those X-ray specs you used to get as a kid. Used to be able to see through people's clothes allegedly.

Senan: Allegedly. And if they were true X-ray specs you'd actually see through the people as well. Except the bones.

Joe: Yeah. Well maybe they were just calibrated successfully. They might have been UV specs. Slightly lower energy.

Senan: But in terms of wavelength we're talking about from 0.01 of a nanometer up to about 10 nanometers. Which in English is...

Joe: Which in English is about a billion waves per millimeter.

Joe: Okay. That's not... it's English but I still don't understand.

Senan: That's a thousand million waves per millimeter. I mean we're getting... these numbers are just bonkers and you can't... on a human scale you can't visualize them. So how are they created? Well one way is if you have high energy electrons. So you know some heavy elements, like heavy metals like lead or whatever, they have electrons at multiple different circuits, like orbits around the nucleus of the atom. And the inner ones would be a fairly high energy. So if you get some of those, if they suddenly stop... like for example hitting a piece of dense metal, that sudden change in speed and direction...

Joe: So with the X-ray, the X-ray hits the metal?

Senan: No, we're talking about how the X-ray gets produced.

Joe: Ah, okay. Right.

Senan: A sudden stop of a high energy electron would be sharp enough to generate a photon of X-ray radiation.

Joe: Right. So like you're talking about not shaking a lead...

Senan: No, no. You're talking about maybe a thing like an electron beam gun like what used to be in the old fashioned TVs, remember the old big televisions?

Joe: Oh the fluorescent tube thing out the back type of stuff?

Senan: Yeah, like firing a stream of electrons from that at a plate of lead for example might be enough.

Joe: Okay. Not going to do it in the kitchen.

Senan: No. But that's just one example. So it needs a lot of energy in the source material to actually generate X-rays because they themselves have so much energy. In nature though they're created by stars and stuff is it?

Senan: Yeah, energetic events in space we'll call them. So could be stars, could be collisions, could be matter orbiting around black holes at high speed, that kind of stuff. So the photons have so much energy that they can knock electrons completely out of their orbits, away from their parent atoms. Subatomic pool.

Joe: That's called ionization.

Senan: Yeah, subatomic pool. Good one, yeah. Or snooker if you get it in the right order. But yeah, they so they can ionize other things that they hit because they've got so much energy. That in other words kicking an atom out that shouldn't be kicked out. So why can X-rays show us bones but not show us flesh? Which is what they're used for diagnostic purposes. It's all about the density of the tissue that they're passing through. So softer tissue like, you know, your muscles, your blood vessels, there's fairly large gaps between the electrons and the X-rays are able to pass through mostly. So there'd be some of them get stopped but not many. But then you come to something much denser like the calcium in your bones or if you have a pin in an old fracture in your leg, the metal in the pin, that kind of thing. Much smaller gaps between the electrons and they stop the X-rays from getting through. So you've got a source of X-rays shining on your leg from one side and on the other side you've got a photographic plate which those X-rays are landing on. And the ones that don't get through your bones make an image on the plate. That's kind of how it works.

Joe: It's also used obviously for airport security scanners.

Senan: Materials analysis, they use it for analyzing crystals and so on. Again it can damage DNA so using X-rays for diagnostics in hospitals has to be done... you can't expose people to a lot of X-rays.

Joe: Is there a limit?

Senan: There's a limit to what you can reasonably expose people to. And even, you know, it's not a hard and fast exact science. So you can have people who have like a very few X-rays that still unfortunately might end up getting cancer from them. It's just a risk benefit kind of thing, you know. So there's also X-ray astronomy. We spoke about infrared astronomy but there's also telescopes that can see in the X-ray band and they can examine some of the most violent things that are happening. Like superheated gas whirling around black holes. Neutron stars which are a very energetic remnant of large stars after they die. Supernova remnants, that kind of thing. And you're talking about these are bodies that have like temperatures in the millions of degrees and the matter that's... the objects, those objects are so hot the atoms in them, the molecules in them are very very energetic.

Joe: But are there satellites that are just X-ray detectors? Or is there like... are there satellites like "Oh we'll, today we're looking at infrared and let's switch over and see what's happening on Channel X-Ray?"

Senan: Well it would be different, it would be different equipment. So I mean it's possible to build a telescope that has different kind of detectors and you switch this one on or you switch that one on. Specifically which ones have combined detectors I don't know, I can't answer that question. But you definitely need different equipment for the different bands of radiation, you know.

Joe: And could you detect... like could you use sort of ground-based telescopes for X-rays?

Senan: You probably could cause I doubt very much that the clouds in the atmosphere would stop them or the atmosphere would stop them. Yeah, you probably could, yeah.

Joe: And finally we come to the absolute monsters of the electromagnetic spectrum.

Senan: Part 2 here.

Joe: I said electromagnetic spectrum.

Senan: Yeah, there you go. Finally. I knew you'd run out.

Joe: Doctor David Banner.

Senan: Gamma rays.

Joe: I just have to say it. Every time I see gamma rays.

Senan: Gamma rays. Oh yeah, the Incredible Hulk. Well, he's a lucky man. Cause gamma rays would usually do more than turn the rest of his green. So wavelength less than... less than 0.01 of a nanometer. So we're talking about the wavelength smaller than the nucleus of an atom. Like really tiny. About a hundred billion waves per millimeter. So that's a lot of energy in every millimeter. So remember we we said that essentially the photons that EM radiation are made from are pure packets of energy. They have no mass, they're just all energy. So these are, gamma radiation photons are probably the most single most energetic objects in the universe. Each individual photon. They're busy little fellows. Yeah, they they they like... nuclear reactions are I suppose the primary source that we can observe. So they're produced by radioactive, you know, uranium, plutonium, etc. Fusion or fission. Fusion is what's going on inside in the sun. Fission is what we do in our nuclear reactors and we're trying to figure out how to do fusion so that it's... we can benefit from lots of free energy.

Joe: But there's not... there's not actual gamma radiation coming off uranium. It has to be reacted with something or hit with a hammer?

Senan: Oh no, no. I mean uranium and plutonium they are producing some gamma radiation. It's one component. There are two other kinds of radiation involved in nuclear radiation which are not on the EM spectrum. They're completely different.

Joe: Okay. Let's not go there.

Senan: But gamma is one of the components of nuclear radiation. So yeah if you have a sufficiently pure sample of uranium or plutonium there's a hell of a lot of gamma radiation coming from it in addition to the other two.

Joe: I don't know where I saw this in a movie or something but apparently the Aboriginal word for uranium means "that which should be left in the ground."

Senan: Under a mountain. Far away. Yeah. So as part of the reason... just to digress slightly... the fact that there's uranium in the magma that's, you know, the lava that's in the center of the Earth is part of the reason why the center of the Earth has stayed so warm. Because the energy just from that radioactive decay is helping to keep the lava hot.

Joe: Okay.

Senan: So what's it used for, gamma rays? Obviously we need to be very careful about protecting people from that radiation. I mean it's lethal. You only need a very small amount of gamma radiation to hit you and it'll kill you or cause give you cancer. But it is used for radio therapy for cancer where it precisely targets tumors and is given in very measured doses to try and avoid damaging the tissue around. It's used for sterilizing medical equipment cause nothing can survive a decent blast of gamma rays. So the bacteria are definitely going to be killed by it. So it's kind of a form of sterilizing things. So yeah that's gamma rays. And it has all kinds of other... there's a lot of gamma rays coming in from the sunlight and other bodies.

Joe: Is this in like... are these things coming out of a nuclear explosion? If someone set off a nuclear bomb you'd have gamma rays?

Senan: Yeah. That's part of the radiation, yeah. But I mean the physical force of the explosion is going to do the primary damage. I mean it's the people who don't get killed by the explosion or burnt by the heat blast from it that are going to suffer from radiation poisoning.

Senan: So we'll just talk about probably nature, one of nature's most incredible spectacles and that's something known as a gamma...

Joe: That's you on a bicycle.

Joe: Have you seen Senan on a bicycle? Just cycling along. It's a sight. Sight to behold.

Senan: Yeah, I mean I'm trying to go in a straight line is... I'm nearly there now. I'm nearly there.

Joe: We'll take the training wheels off soon.

Senan: Well yeah and the guy that walks in front of me with the flag, I won't need him much longer. So gamma ray bursts. They are the most powerful explosions in the universe that we know about. And they're things like massive stars collapsing into black holes or neutron stars merging with each other. These are the kinds of explosions in space that produce them. A gamma ray burst releases more energy in a few seconds than our sun will release in its entire ten billion lifetime. Like it's mind-boggling amounts of energy. You can't... there's no way you can picture that in our poor little monkey brains. But it's basically Einstein's E=mc2 in action. So that's matter and energy. So matter literally converted directly to gamma ray energy because of it was annihilated during a very forceful event. They're so powerful that if one happened within 5,000 light years of Earth... now remember the sun is eight light minutes from Earth. So 5,000 light years is a long, long way away. There's a lot of other stars closer to us than that. If one happened closer than 5,000 light years from Earth, it would probably kill everything alive on the surface of the Earth.

Joe: But not for 5,000 years.

Senan: No, well I said closer than 5,000 light years.

Joe: Okay. Well say it was 4,500 light years. But in the future. It could be happening. They could be barreling towards us right now.

Senan: Yeah because nothing travels faster than the speed of light which is the speed the gamma radiation will be traveling at. So we won't see this explosion happening before the gamma rays hit us.

Joe: So we might as well just live as if there's a giant gamma tidal wave hurtling towards us.

Senan: Yeah. Let's party like it's 1999. Now look, where do you go after that? I mean follow that, gamma ray bursts.

Joe: Well gamma ray bursts are... but I mean is that it though? Is that the upper limit? Is that as far as we know?

Senan: That's as far as we know, yeah. That's as far as we know.

Joe: But is it possible that there's like gamma plus or like lambda or whatever, wherever you would go after gamma?

Senan: We're kind of not only are we reaching the limit of our knowledge, we're reaching the limit of my knowledge of mathematics too. So I apologize listeners. We should have found this out.

Joe: Okay. We're going to say that gamma rays are the daddies.

Senan: That's what we know of at the moment, yeah. But as the EM spectrum, it's something else. The amount of variety that one substance... it's not even a substance, that one phenomenon we'll call it. You know everything from radio waves that are kilometers long down to these gamma ray bursts that are like minuscule.

Joe: And of course the lines in between all of these different categories are pretty arbitrary I imagine.

Senan: Oh yeah. I mean these different bands we've been talking about, gamma rays, X-rays, ultraviolet, blah blah blah. They're all human divisions. I mean there isn't like a sharp change when you hit the border as it were. You know. So something that's slightly on the gamma ray side versus slightly on the X-ray side, very little difference between them.

Joe: Well you want your radiologist to know. Definitely. What did you say? Did you say gamma ray? No, no. No X-ray. It's definitely an X-ray.

Senan: Yep. Yep.

Joe: Well look, that was a hell of a tour around the electromagnetic spectrum. Quite a comprehensive one.

Senan: Yeah, yeah. We've filled an hour. I can't believe we filled an hour. When I looked at all the notes we had made I said we'll be lucky to get to half an hour. So it's funny the way time just drags on.

Joe: It doesn't drag on. Just dragged on. It flew along.

Senan: We're traveling too fast. I bet you that's it. We've accelerated towards the speed of light.

Joe: We've accelerated it so time seems slower. So if you actually speed up this podcast time will go slower for you. So slow it down and time will go faster. There you go.

Senan: My brain hurts.

Joe: I know. Mine too. I think we'll leave it there. That's enough with the science for this week. I'm Joe.

Senan: And I am Senan. And we'll see you all again next week where we will not be talking about the EM spectrum.