In this episode we answer two different but equally important questions. What would the headlights on a spaceship moving at the speed of light look like, and are there actually aliens out there?
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Chris
Hello and welcome to The Astroholic Explains. I am Chris
Alfredo
and I am Alfredo, the Astroholic
Chris
And today we are doing a slightly different episode…
Alfredo
One of the comments from our lovely listeners was this “you guys sound great! You don’t even sound drunk.
Chris
We’re not drunk.
Alfredo
No. Usually I do The Astroholic Live with cocktails, but most of the podcast has being recorded in the morning.
Chris
Yes, like 6am when it’s quietest, so we don’t really want to get traffic noises! But we’re going to try something different because we have just recorded an Astroholic Live and we have had some cocktails leftover so we’re going to do this
Alfredo
Yes, with cocktails. So hopefully, I’m not going to be a mess by the end of it
Chris
but I hope you are.
Alfredo
I might get very ranty so brace yourself.
Chris
Okay, should we start?
Alfredo
Yes! Let’s start! Cheers. So what questions have you got for me today?
Chris
Today, we’ve got two questions from our listeners.
Alfredo
Wonderful.
Chris
And I think I’m going to start with what I think is the much, much more complex question.
Alfredo
Okay,
Chris
this question… is missing and I can’t find it, where the hell has it gone?
Alfredo
Good stuff. Very strong start, Chris.
Chris
The first question comes from Scott on Twitter whose handle is @unlikelylad. Scott asks: “What would happen if a vehicle traveling at the speed of light turned on some headlights?”
Alfredo
That is a very, very good question.
Chris
It actually took me a while to actually comprehend what he was trying to ask. Because I just assumed “well, the lights were turned on.”
Alfredo
Yes…
Chris
But it’s at light speed and light is… What is happening? Because if you’re traveling at the same speed of light, does the light even appear? Does the light show? Does the light form a beam? Does it form a beam behind it?
Alfredo
So those are all very good questions. What do you think?
Chris
Oh god! Me?
Alfredo
Yes!
Chris
Right. Okay, so if the car is going at the speed of light, which is 9 [mumbles] point 3 kilometres per second… meters per second…. I don’t know what it is. I know, I know there’s a three in it. No, I’m thinking of the distance of the sun.
Alfredo
Is it 93 million miles to the sun?
Chris
Okay.
Alfredo
I don’t know! I’m asking because I only know it in kilometers!
Chris
We can check that after but I think it is. Anyway that’s not the point. The point is the car’s traveling at the speed of light and if it then tries to put light out in front of it to light its way, I think the light would appear like if you’re looking into the headlights, it would look like they are lit up. But if If they were surrounded, if everything was dark, they wouldn’t be forming a beam of light in front of it because it would be traveling at the same speed. So maybe the front of the car would just glow and somehow leave like a sort of long exposure beam of light behind, it as it goes.
Alfredo
Okay, I think we need to break it down a little bit, so is a bit clearer. So first of all, the easy and a bit of a cheap way to answer this question is just saying that nothing that has mass can go at the speed of light.
Chris
[Groans]
Alfredo
I’m gonna give a different answer… I’m just pointing out the rules of physics! It’s our playing field, and we need to deal with that. Okay, so this car cannot exist, but let’s assume that it can. Let’s assume that we can have something that goes very, very, very close to the speed of light. We need to introduce something that an Italian physicist, Galileo Galilei, came up with a few centuries ago, and it is the concept of an inertial frame of reference.
Chris
WHAT?
Alfredo
I will explain, don’t worry!
Chris
Sorry, that was an aggressive what… [Sips drink] I was about to say, what is that? Good cocktail…
Alfredo
Good cocktail, I know. I’m getting ranty and you’re getting aggressive. So this might be a one-time-only experiment. So what is this inertial frame of reference: it is the idea that if a reference is either still or moving at a constant speed, the physics should behave in the same way because you don’t have any apparent forces. There is no acceleration.
So if an object is moving at a steady speed in a straight line, it wouldn’t be able to feel the there is any acceleration. So everything according to the laws of physics should behave completely the same as if you are in a place that is not moving.
Chris
So it would look like it does on a motorway.
Alfredo
What do you mean by that?
Chris
Well, you said it would look the same, is that not what you meant? Well, like you looked at a car on a motorway, and you can see the lights and you can see…
Alfredo
No, no, no, we’re not at the car yet. We’re still at the inertial frame of reference. That is the concept that we’re starting with. Now we need to add a little bit more. So imagine that you have this initial frame of reference, so you cannot tell if it’s moving or not. You are on a train that is moving at a constant speed. So inertial frame of reference, you cannot tell that it’s moving. Let’s assume that it is completely blocked off. No windows for anything. And for example, you have a machine that measured the speed of a bullet, that you’re going to shoot. Okay?
Chris
Okay.
Alfredo
So you shoot the bullet and you measure a certain speed for the bullet. Now, there is another observer that is outside the train, and they can see that bullet. You shoot the bullet. And so they measure the same speed for bullet plus the speed of the train.
Chris
Yeah.
Alfredo
So those two speeds are summed up. The physics doesn’t change, the bullet appears to you to move at a certain speed and appears to the external observer of moving at a different speed.
Chris
That makes sense. It would be like if you were inside that train and say there was a window and you looked out, what you would perceive would be a still bullet. Because you would be moving at the same speed as it and it would kind of look like it was just in the air
Alfredo
If going at the same and parallel [I said opposite in the broadcast and that’s wrong!] velocity yes, then you absolutely correct! Or think if you are on a train at a constant speed, you can juggle, because you can throw a ball up and still be moving at the same speed as the train. But for an external observer looking at this… Or you’re just sitting on the train, so for you, you are still! But for an external observer, you’re moving at the speed of the train. Right?
Chris
Okay, yep.
Alfredo
Now, what happens if you have a torch and you measure the speed of light on the train? The speed of light is slightly less than 300,000 kilometres per second.
Chris
I knew there was a three in it.
Alfredo
Well done.
Chris
Yes.
Alfredo
So you measure the speed of light, you get a certain value. The external observer gets the same value. Dun, dun, dunnnn! Why do things change for the bullet, but not for the speed of light? The reality that we observe is what happens to the light! And the way we measure the bullet is not… because the velocity of the bullet and the train are so low that is just the approximation to the real relativistic reality. So, you should always consider that the way you calculate the proportion between the inertial frame of reference, will always lead to the speed of light in a vacuum being constant.
Chris
…Okaaay
Alfredo
And no matter what you do, you should always do the calculation correctly. In the case of the bullet, you would have the same complex formula etc. that would prove to you that the speed of light in vacuum is a constant but it’s so much easier to just add the two velocities than doing a complete calculation unless you have light. So far so good?
Chris
Okay, so far.
Alfredo
Now, we can get into our car. Okay, so let’s assume that is less of a car or more of a spaceship. And for some reason we want to turn on headlights, they will still leave the car at the speed of light. And we are assuming that as though the car is moving almost at the speed of light, that it will still be slightly ahead.
Chris
So it will be like a glow…
Alfredo
Things get extremely complicated. So what’s happening, I imagine, based on what I can remember of the physics formula, that it would very much happen like a Doppler shift. So if you’re not familiar with the term, it is what happens when, maybe, you have an ambulance coming towards you, because the speed of sound and the speed of an ambulance are quite similar as the ambulance move towards you, it sort of squish the sound waves emitted by the siren.
Chris
So it makes the pitch go higher.
Alfredo
Yep. And then the wave left behind,
Chris
the wavelength elongates again as it gets further away. It’s what makes the different tone coming towards you, and as it’s going away from you.
Alfredo
Absolutely.
Chris
I would do an impression, but I’m not that drunk.
Alfredo
All right! So we need to drink more! Let’s assume. So top of my head. I would say that if your car is going at 10% of the speed of light, and you have yellowish headlights. The squishiness of this Doppler shift should probably push it into blue-indigo-violet
Chris
Interruption!
Alfredo
interrupt me!
Chris
When talking about visuals is the Doppler effect not called redshift?
Alfredo
It is. But if you’re moving from the yellow to the violet, is it a redshift?
Chris
Oh, I don’t know… I always thought that… Well, no, I just thought that redshift didn’t necessarily only apply to red shifting, which, I guess is the name that implied it would. But I just thought it was like it meant the spectrum.
Alfredo
It meant the spectrum. It’s not that the red is shifting as you’re shifting to the red. So what Chris mentioned, it’s this phenomenon in which galaxies, since the universe is expanding in all directions, and all the galaxies are going away from each other (unless they’re really close and bound by gravity), appear to be redshifted. So since they’re moving quite fast, their wavelengths are shifted towards the red. So a galaxy that might appear yellow if it was here, it would appear more red if it’s very far away. In this case [of the car] it would be a blue shift.
Chris
Okay, because it’s the different part of the spectrum.
Alfredo
Okay, let’s assume you have your position lights to the back and again they are yellow, then it will definitely shift into the red or near-infrared. So you might stop being able to see the back of the car.
Chris
Wow.
Alfredo
Okay, well see it with your own eyes. With that, I would say that if you go from 10% to 50% you’re jumping into the ultraviolet for sure. At 99.9% of the speed of light even though your car is the emitting yellow light, what is actually being thrown out is x-rays. So you are right, there is a glow, but it’s still a glow that is moving, definitely at the speed of light, but also moving forward. So you have beams, but the beams are now x-rays because [the photons] are being pushed together.
Chris
And they’re always coming out the front? It’s not like the beam would trail? Obviously they trail behind, I guess because it’s moving at the same speed.
Alfredo
But also a lot of X-rays in hospitals are created by different sources, some radioactive sources, etc. We have ways to make x rays using almost light-speed, synchrotron radiation, they emit x-rays. Okay, so.. No. the fake relativistic car doesn’t produce anything in any efficient way. I think there’s also some weird effects in the car. So you need to consider that moving at speeds close to the speed of light will change how time passes for you and how the world looks. And also as you pass objects, their angles will appear to change, like if they’re rotating… there is something called the Lampa–Terrell–Penrose effect. And it just makes things a lot more complicated. So if you’re in a car at the speed of light, and you’re turning on your headlight is not really gonna matter much because the world from how you see it in the car, it’s nothing like you ever experienced it before.
Chris
I can believe that. I mean, it’s physics. But I mean, I can believe it’s nothing that you’ve ever experienced before.
Alfredo
That’s what we are here for.
Chris
Well, Scott, I hope that answers your question, and that you learned a little something today. Are you ready for the next question?
Alfredo
I am ready for the next question! Hit me.
Chris
Right, the next question comes from Michael, who is @MrPlantGeek on Twitter and he asks something that probably quite a few people would like to know. How likely is it that aliens exist?
Alfredo
Well, that’s a very good question. It’s a question asked very, very often, because,
Chris
because aliens are damn cool!
Alfredo
Aliens are damn cool! And also, we are quite negative and cynical about our species. And we really want to believe that there’s something better out there.
Chris
Or we’re negative and pessimistic about our species and we’re just begging for something that’s going to end us!
Alfredo
That too
Chris
Like you’ve got the entire history of sci-fi, where I would guess that most aliens in sci-fi are things that want to eat us. Well, maybe it started that way. I think there’s probably been a shift over time, away from horror and aliens that want to eat us to more aliens that want to educate us or befriend us.
Alfredo
I think the two always went hand in hand. And I think it’s symptomatic of projection.
Chris
Yeah.
Alfredo
I’m just seeing human nature. Yeah, seeing us as the best we could be and as the worst.
Chris
I think you finished another podcast recently with “We are the universe observing itself.”
Alfredo
Yes. It’s a Carl Sagan quote.
Chris
And it’s quite appropriate for this. It’s how we project ourselves onto the universe. We see our flaws. And we want to give them this grand, romanticized idea, or maybe even scapegoats. These are not just our flaws. These are prevalent in nature across the universe,
Alfredo
Like the Greek and Romans did with the gods. The ideas going on sci-fi… It’s just so obvious that sci-fi is not there to tell us “uuuh there’s aliens, jetpacks, or other stuff!” And I can rant about “serious writers” who want to foray into sci-fi as they think it’s just… I don’t know, hoverboards and stuff. Sci-fi is a way to discuss important themes with a futuristic twist or alien twist or something completely out of this world. Yes, fun and exciting but talking about humanity as it is. But let’s go back to the question. So how likely is that there are aliens out there? I think is extremely likely.
Chris
Yeah, definitely.
Alfredo
It’s just.. there’re too many planets, there is too much stuff that we cannot be the only possible example of life in the whole wide universe. We believe that there are planets around almost every star in the Milky Way. And there are a hundred billion stars in the Milky Way. The Milky Way is one of about 2 trillion galaxies in the visible universe,
Chris
Just in the visible universe
Alfredo
So you can do some random statistics and just put very strong constraints and the probability that is just us are astronomically low! I remember there was a paper, I think, last year or a couple of years ago that showed a lot of these estimations come from the Drake equation, you might have heard it, which is just..
Chris
The Nathan Drake equation?
Alfredo
No, not the Nathan Drake Equation! It’s this equation about the number of civilizations in our galaxy, for which communication is possible.
Chris
So that’s not even going on tiny little life form?
Alfredo
No, it’s about SETI. Not only intelligent life, intelligent life that can communicate at a certain level of technology.
Chris
Yeah.
Alfredo
So we are only in this category in the last 70 years. Even like, even after we invented radio, like the good thing about the radio was that they bounce off the atmosphere and don’t leave Earth. You can communicate between continents. What you have is this equation that is just trying to establish ‘what is the number?’ And it multiplies how many stars you form per year in a galaxy, the planets that you have around those stars are good, how likely those plans have the condition for life. Although many, as we discussed before, could have the right condition for life, not all of them might develop. Then you need to develop intelligent life. Then that intelligent life needs to develop ways for interstellar communication. And on top of that, you need to have that communication going for a certain amount of time. If we end up destroying ourselves with war, global warming, something else, we’ve been able to communicate for a hundred years? In a hundred light years, you have a huge amount of stars around. But still…
Chris
the people who pick up a signal as well need to be looking and listening in the right places at the right time!
Alfredo
Yes, they need to be. So it’s quite a small number. And a lot of very conservative estimates that want to push this number to 1. There is one civilization, and it’s ours. But even with that, even considering that you still have 2 trillion galaxies out there, that even if the conditions for life are only possible once in the history of a galaxy, then you still have 2 trillion civilizations out there that we probably never going to be able to contact but they’re out there.
Chris
I would like to comment on this Drake equation because for the little I know about it, I would say that it is flawed. The reason that I think it’s flawed is that, yeah, it’s it makes sense, but I think it can only be the lower end of the estimate.
Alfredo
Oh, yeah!
Chris
There can only be more than what is the outcome of this! This is all based on conditions for life that we understand. There could be other types of life that evolved, grew into a developed intelligent species capable of contact across the stars, but they live in different conditions that we could never expect them to thrive in. So we might not even be looking in the right places at the right wavelengths, the right sounds, sights, contact might be happening. We’re just not seeing it.
Alfredo
Absolutely.
Chris
That would fall on top of the base number from the Drake Equation.
Alfredo
But what I gave you with “one” was the pessimistic estimate. The issue is that the numbers, apart from star-formation rate of the galaxy and the fraction of planets around the stars, all the other numbers are arbitrary. We are not quite sure what makes life possible on a planet. Yeah, you need to have certain ingredients we discuss in a previous episode, but we are not a hundred percent certain that that is the perfect recipe, that this is how our planet needs to be for life. And absolutely, you’re right, we might not be able to communicate with intelligent species because they have not evolved like us. And another thing that we haven’t considered is time. If you want to be extremely pessimistic, and we know a one example of intelligent civilization, us, throughout the entire visible universe is pretty much a chance in about two trillion. But what if you also want to consider the entire history of the universe? So even being loose and say, okay, nothing could have happened in the first 3 billion years of the universe, because you have the peak of star formation, there is a lot of powerful UV light, yes, you have big stars, etc, but maybe not enough of the building blocks for planets and life, etc.
Chris
In the way that we know
Alfredo
In the way that we know it. Let’s assume that we are going “humanity is the only intelligent civilization across all the visible universe across all of time”. That means there is a chance in 10 billion trillion. That is so tiny, so impossibly tiny. Listen, I’m not saying that there are little green people on Mars. But if you think that we are alone in the universe, you are wrong.
Chris
That’s impossible.
Alfredo
It is so unbelievably unlikely that we really have to come up with a very good explanation for why we are alone. And the idea of science, especially when it comes to astronomy, is to push humanity far away from a special place as possible. We hate the fact that everything seems to be quite well fitted for us. Physics needs to work out all these reasons beyond humanity. We are just a happy accident or just an accident if you’re very cynical, and we are most likely just one of the many billions of civilizations, they are now alive across the universe. And I would like very, very much to find out about any other types of life forms. And you see you’re actually right. I’m very hopeful about what we might find under the icy ocean of Europa and Enceladus, the moons of Jupiter and Saturn respectively, because they have hydrothermal vents, and salty oceans. That could be complex chemistry, actually, we know there is some complex chemistry, there could be enough complex chemistry and energy to sustain life. Probably not some sort of Atlantis civilization, or merpeople. But maybe simple life. And that will tell us that we’re not that special. Maybe reaching levels of civilization without destroying each other is very, very difficult in the universe. Maybe it’s not. Or maybe they’re just horrible creatures that just want to eat us. Who knows?
Chris
I think the right now a lot of people would vote for that,
Alfredo
Or maybe are the one that will inspire us to be better..
Chris
I’d like that kind of optimism. But I really can’t help but think that if there was another big intelligent species out there, I think there’s a fair chance that people would react in the same way as they do in films. And by people I mean, governments and people with weapons. I don’t think peace would come easily.
Alfredo
Then maybe it’s true that they are observing us and just waiting for us to either self destruct, or
Chris
Or calm the fuck down.
Alfredo
Or calm the fuck down.
Chris
This has been good. Two very good questions.
Alfredo
Yeah, and aliens. If somehow you’re listening to this podcast, please do know that we are trying our best to calm the fuck down.
Chris
And also like and subscribe on all of the different channels please.
Alfredo
Yes, please share it with all your friends across the galaxy. Thank you.
Chris
Do you have any burning questions for the Astroholic? If so send them into me @illucifer on Twitter, and I will spring it on him in an upcoming episode. See you next time!
Main image credit: Bruce Warrington on Unsplash