Where does it begin? Where exactly is this line which we have to cross in order to be in “outer space”? The Earth’s atmosphere is about 100 km thick. Well, I say ‘thick’ but it’s all relative. The Earth’s diameter is almost 13 000 km. Compared to this, the atmosphere is like a thin sliver of air encapsulating a gigantic rock. If the Earth was the size of a football then the atmosphere would be a layer of about 1 mm on its surface. In that sense, we have a really thin layer of life-sustaining gases (oxygen, for example) keeping us and all living things alive on this planet. This atmosphere also acts as a shield or filter. It keeps certain harmful radiations from reaching the surface of the Earth. The sun not only gives us light (the visible part of the electromagnetic spectrum) but also throws in some infrared and ultraviolet (UV) radiation. UV can be harmful if exposure to it is prolonged. There are some types of UV which are even more dangerous but, thankfully, the atmosphere absorbs them before they reach us. The atmosphere also acts like a trap in that it stops the sun’s infrared radiation from escaping to outer space once they bounce off the ground. The atmosphere then acts like a blanket and keeps the Earth warm.
Given there is no traffic or speed limit, we could easily cruise at speeds of about 100 km/h on the motorway. In fact, with most cars, it is not difficult to achieve such speed and, often, we overlook how effortless it is to reach that speed. Now, instead of driving along a road at that speed, imagine driving vertically upwards from the ground. At that speed, we would be in outer space in about an hour! Wouldn’t that be great! Why then do we need such powerful and ginormous rockets to take us to space when, seemingly, a car has what it takes to do this journey in an hour? I’ll let you ponder on that for a while.
First of all, let’s see what is “out there”; what is beyond that thin sheet of air separating us from space. Our closest celestial neighbour is the moon. Earth’s one and only natural satellite. However, if we consider artificial (man-made) satellites then there are about 3 000 of them in operation. Yet these are but a fraction of the swarm of 24 000 or so objects (including debris from old satellites) in orbit around the Earth. A real junk yard in orbit just above our heads! Fair enough, without those satellites there would be no telecommunication or global positioning or spying on rogue states but just imagine the sheer amount of stuff hovering up there. But before the race to space began, some 55 or so years ago, the moon was the only thing orbiting our planet.
The Earth isn’t the only planet to have a moon. Mars, the fourth planet from the Sun, has two moons. One is called Phobos, after the Greek god of fear, while the other is Deimos, the Greek god of dread. I wonder whether we should be scared of them or whether they are a pair of cowards afraid of the mighty Greek god of war, Mars. Either way it doesn’t matter as, at least, they have a name to go by. We call our moon, Moon. It’s like naming your child, Child.
Earth, Mars and the other six planets and their moons as well as a whole bunch of asteroids all collectively go round the Sun. The Solar System, as professor Brian Cox has shown, is full of wonders, to say the least. That the sun is at the centre of the system is not a subjective claim. Previously, we used to think that the Earth was the centre of the whole Universe, let alone the Solar System! And this is purely out of ignorance and, subsequently, ego. Even if we think of it in relative terms, the idea that the Earth is the centre around which everything else revolves just doesn’t make sense. Let’s take an example: You are comfortably sitting in your car in the back seat admiring the scenery as it goes past your window. The landscape sweeps past you, framed by the window, like a movie about The Great Outdoors. Relative to you, you are not moving, you are sitting quietly and contemplating the lampposts, trees and mountains going by. But we clearly know that those very lampposts, trees and mountains are not actually moving. They are (or, at least, should be) firmly planted and with no means to move about on their own accord. Relative to them, you are the one moving as you go past them in your car. This picture is fine either way you look at it even if we didn’t know that, in the bigger picture, it’s you and your car that’s moving and the scenery stationary. However, the same reasoning cannot be applied to the geocentric theory; the theory that plants the Earth at the centre of the Universe. The Universe, you see, doesn’t have a centre. It doesn’t make sense to speak of our Universe as having a centre because the geometry of the Universe, the shape of the Universe, is not that of a sphere. Because we are so used to moons, planets and stars to be round in shape, we could easily assume that the Universe is simply a much bigger ball containing everything there is. On top of that, the idea that the Universe sprouted from a Big Bang and grew bigger and bigger, inflating like a balloon outwards from its centre, could also lead us to think that this is how the Universe is.
A box is a cube. A ball is a sphere. The Great Pyramid of Giza is, well, a pyramid. We are very familiar with these shapes. They refer to solids or three-dimensional objects to which we can relate easily. The Universe, however, goes beyond three dimensions. We have to think of it as a four-dimensional object. What that means is that it has one added piece of information which 3D objects don’t have. Take a sheet of paper. Place it flat down on the table. Draw a line on it from left to right. Next, draw small circles from top to bottom. Finally, just scribble on it from one corner to the other. In each of these cases, you left your mark on the surface of the paper. This sounds obvious. But what we have to realise is that there is no way to draw a line vertically upwards from the paper towards the ceiling. Even suggesting this sounds strange. How can you draw above the flat sheet of paper? This concept of writing above the paper just doesn’t make sense. So, relative to that piece of flat paper, ‘above’ is something alien to it. All the paper knows is what’s flat on its surface. It is restricted to the 2D world only. It has no clue or awareness of the third dimension, of what’s up or down.
Take the example of a 3 story building. Imagine you are somewhere in that building and you need to tell your friend to come and find you. If all you say is that you are on the right hand corner of the building then your friend would have to check the right hand corner of every floor until she/he locates you. But thanks to 3D, not only can you give your location as being on the right hand corner but you can also specify which floor you are on. With 3D we can have one extra piece of information which 2D won’t be able to give us.
Similarly, the Universe has this extra level of information which we, 3D beings, aren’t aware of. The shape of the Universe, therefore, cannot be exactly specified in terms of 3D objects but we need a fourth level of dimension to have a more accurate picture. Nevertheless, with some approximations and analogies, we can have an idea of what shape our universe is and why, therefore, it is meaningless to speak of the universe as having a centre.
Imagine an ant crawling on a beach ball. It starts off from a point on the surface of the ball and crawls in a straight line in any given direction and it keeps in that direction throughout its journey. If it keeps along this path then after a while it will return to the point it started off from and thus complete one round trip along the equator of the ball. It could well have started off from a different point, crawl in a straight line along some other direction, keep moving along that path and end up where it had started. There is no one point on the surface of the ball that can be designated as the point from where all journeys begin. Any point could lead to the same type of journey round the ball. So to speak of a centre on the surface of the ball is meaningless. Also, the ant is limited to crawling on the surface only and not to jump or fly above the surface. In that sense, it is restricted to the flat 2 dimensional ‘world’ on the surface of the ball; it is unaware of the third dimension called ‘above’.
Now consider the world we live in as the ‘surface’ of the Universe’. In the same way that there cannot be a centre on the surface of the beach ball, there cannot be a centre on the ‘surface’ of the Universe. We cannot assign a point in space out there as the centre of the observable Universe. Neither can we place the Earth in such a privileged position and claim that it’s at the centre of the Universe.
Let’s carry on with that analogy. The surface of the ball is curved which therefore leads to the fact that the ant could come back to the starting point in its journey round the ball. Not only that, the size of the ball doesn’t change. If it were getting bigger and bigger as we keep inflating it while the ant trods along its path along the surface then there is no way the ant will return to its starting point if the ball keeps inflating forever. (Assuming, of course, such a ball exist!) If we now translate this to our Universe, what this would mean is that, if we were to follow a straight path through space from, let’s say, the Moon and keep moving in the same direction then we could, after some time, come back to the Moon after we’ve done this round trip across the Universe. This would be possible if the ‘surface’ of the Universe was curved just like the surface of the ball. But that’s not the only condition, though. What we also require is that the Universe is not getting bigger and bigger just like the inflating ball. If it were, then we would never return to where we started from (in this case, the Moon). So, first of all, there is the possibility that the Universe is curved like the surface of a ball and, secondly, that it’s expanding like an inflating ball. There is also the possibility that it’s neither curved nor expanding. In which case, we would not be using a beach ball as an analogy but a sheet of paper of finite size. How can we test which one it is? Well, we have to take some measurements. Observing stars and galaxies moving away from each other could mean that the Universe is expanding. As for whether it’s curved or not, we have to look elsewhere. Einstein‘s General Theory of Relativity is the best place to start looking for answers about the shape and curvature of the Universe. His theory gives us all the tools we need to determine this. We are not going to delve into the details of this theory in this blog but it suffices to say that Einstein has provided us all the necessary mathematical framework on which we can build our picture of the Universe. With powerful telescopes and other sensitive instruments, we can test the results derived from General Theory of Relativity. So far, what has been derived from or predicted by the General Theory of Relativity has turned out to be in line with our observation and with our rigorous tests. Therefore, we can rely on this theory to give us an accurate picture of the shape of our observable Universe.
In the previous blog, I spoke of the electromagnetic spectrum. The most familiar part of the spectrum is the one visible to the human eye: light. The other constituents also carry information but invisible to the naked human eye. With certain instruments, we can capture the other electromagnetic radiations and gather information from them. We use radio telescopes to detect radio waves coming from space. We also have x-ray and gamma ray telescopes which look out for x-rays and gamma rays cruising the interstellar space. Because x-rays and gamma rays are absorbed by the atmosphere (we should be grateful for that) we have to place those telescopes in orbit around the Earth outside of the atmosphere. Radio wave telescopes, on the other hand, can sit comfortably on the ground and gaze at the stars. Radio waves, it turns out, are not absorbed by Earth’s atmosphere. The same star which emit visible light, could also be emitting x-rays but unless we use the x-ray telescope to detect that, we wouldn’t be able to visualise what type of information the x-ray emitting star is sending out. This is analogous to you going to the hospital and showing the doctor your sprained ankle. With her eyes, the doctor can clearly see the swollen part of your ankle. But that’s about it. That’s all the information visible light coming from your foot can tell her. But with an x-ray machine, the doctor can now see what’s going on inside your foot. This is information she couldn’t get before. Whether you fractured a bone or not, she can clearly tell that from the information captured by x-ray.
So you see, there is a lot of information and detail that we can gather from outer space by making use of the whole of the electromagnetic spectrum. Pulsars are a good example of this. Pulsars are a type of stars which send out bursts of electromagnetic radiation (radio waves and gamma rays, for example) at regular intervals. Pulsar is short for ‘pulsating star’. Without the relevant instruments, we would not have been able to discover those fascinating celestial phenomena. There is a whole world of amazing and awe-inspiring moons, planets, stars and galaxies out there to be discovered. Thankfully we have a panoply of instruments (which are basically extensions of our senses) to help us find those objects.
Space exploration is another extraordinary human endeavour. The desire to explore and the excitement to be the first to discover something new are what drive us to seek new worlds. And this is a deeply humbling experience. When we look out to the stars and realise that our solar system is just one of many, when we peer deeper into space and realise that our galaxy is one of many, when we look further still into the recesses of space, we realise how small, how miniscule our planet is compared to the vastness of space and not only that, we realise how ephemeral our existence as a species is compared to the age of the Universe. We, Homo sapiens, have been around for about 200 000 years. The Universe, on the other hand, has been around for some 14 billion years. We are but a mere fraction (about 1/70 000) of the existence of the Universe. To put this in perspective, imagine the age of Universe to be the duration of a day. That’s easier to conceive than having to handle such big numbers as 14 billion years. So, if the Universe was 1 day old then human existence would only be about 1.2 seconds! Just small tick on the big clock of existence. That’s nothing. That’s almost unnoticeable. But yet, in that fleeting moment of human existence, we have achieved a lot in terms of understanding the Universe and the laws that govern it. And in the last few decades, we have found so much more about the Universe than what we knew of in the last few centuries. This is to say that our knowledge and understanding of science grows exponentially. Up until the invention rockets and spacecrafts and radio telescopes, our picture of the Universe was very narrow. We only knew of a handful of stuff out there compared to the tremendous amount of data we’ve gathered from decades of exploration and observation. We’ve found planets which resemble our own and which could potentially harbour life as we know it. We’ve found black holes and quasars. We’ve mapped the whole sky not only in breadth but also in depth. More importantly, we’ve been able to see so much deeper into space that we’ve been able to glimpse how the Universe was at an early stage of its life. To look into the distance not only tells us how far away something is but also how old.
Let’s reflect on this for a moment. Even light takes time to travel a given distance even if it has an enormous speed, even if it holds the world record for the fastest moving thing in the Universe. When I say light I also mean every other member of the electromagnetic spectrum. Be they radio waves or microwaves or gamma rays, all electromagnetic radiation travel at the speed of light. That’s a staggering 300 000 km/s! In kilometres per hour (or kph) that’s about 1 billion. The fastest car in the world can only do about 430 kph. Big deal!. So, 1 billion kph might seem huge (and it is huge compared to our fast cars) but on the scale of the Universe, which is even huger, the speed of light becomes quite banal. It takes light about 8 minutes to reach us from the Sun, on average. At top speed, it would take the Bugatti Veyron Super Sport about, well, 40 years to travel that same distance, assuming of course that there’s enough fuel to power this incredible trip. This is just another way of saying that the Sun is really, really far away even though it looks like a big yellow spot in the sky. The scale of the Universe is stupendous. It no longer makes sense to talk in terms of kilometres or even thousands of kilometres just as we might do here on Earth. The distance from the Earth to the Sun, for instance, is about 150 million kilometres. But Earth is still relatively close to the Sun. The furthest planet in the Solar System, Neptune (the Roman equivalent of the Greek Poseidon), is about 4 500 million kilometres away from the Sun, on average. I say on average because the path Neptune follows around the Sun is not circular. If it were then the distance from Neptune to the Sun would always be the same. The radius of a circle is constant. But like every other planet in the Solar System, the path Neptune traces around the Sun is elliptical. An ellipse is like a stretched circle. So it has one radius longer than the other one and the two radii are perpendicular to each other. What that means is that, as the planets go round the Sun, sometimes they are very far and sometimes very close to the Sun. So, back to our Roman god Neptune. Neptune is about 30 times further away from the Sun compared to the Earth. And this is not yet the edge of the Solar System. There are other bits and pieces floating in space, beyond Neptune, which are also revolving around the Sun. They are not planets but, like asteroids, they go round the Sun. One of these objects is called Pluto. Pluto used to be considered a planet but it has been denied this privilege a few years ago now. Well, it’s not fair to say that being a planet is a privilege but to be called a planet and then be stripped of this appellation in the face of your peers must be an embarrassing moment. But I don’t think Pluto cares about this. It is now considered to be a dwarf planet like a whole host of other dwarf planets orbiting the Sun in the far reaches of the Solar System. This region of the Solar System is called the Kuiper Belt and it extends to about 15 billion kilometres from the Sun. That’s roughly 100 times the distance from the Earth to the Sun. Already this is becoming difficult to imagine. Such mind-boggling scales is way beyond our comfort zone. We are more used to things ranging from centimetres to a few metres. Anything outside that range is beyond the human scale. So to speak of a system which is 30 billion kilometres in diameter is humanly inconceivable. We may believe that we understand such distances but we can’t. Our brain doesn’t have what it takes to visualise such big numbers. However, we are a bunch of clever apes so this is why we came up with the concept of scale to allow us to compare things we are familiar with to things which lie beyond that ‘normal’ range.
Speaking of comparison, let’s see how long light from the Sun would take to reach the furthermost part of the Solar System compared to how long it takes to reach us. We already know that it takes 8 minutes to reach us. Light, as you would recall, travels at 300 000 km/s. To cover a distance of 15 billion kilometres, it would take about thirteen hours and fifty-three minutes! Another way to put this is this: If you were to send a text from the edge of the Solar System saying that you were waiting for everyone to join you there for a party, that text (transmitted via microwaves) would take 13 hours and 53 minutes to reach the Sun. We, here on Earth, would intercept that text 8 minutes sooner or in about 13 hours and 45 minutes. By that time, you would probably have given up on waiting and left to party somewhere else. And there is no way we could have received that message any sooner as nothing travels faster than light.
Similarly, imagine you witnessing an extraordinary event from your privilege position there at the edge of the Solar System. Let’s say, purely for the purposes of this example, let’s imagine that you saw a spacecraft in the shape of a submarine drifting past you and that there were some crazy chaps in that yellow spacecraft disguised as the Beatles. Almost as a reflex action, you took out your camera and filmed that event while simultaneously transmitting the images over to us here on Earth. This ‘live’ event you were broadcasting to us would reach us at the very earliest, 13 hours and 45 minutes after the event. When we would actually receive that video from you and start watching the Beatles drift by in their yellow submarine, it would only be an old video. Old by almost fourteen hours. What we, here on Earth, think is a ‘live’ event is actually something that has already happened and probably even ended by the time it took to reach us. The submarine could have been long gone by the time we started watching that video. This is a very important concept to grasp. What we see out there in the far reaches of space is actually images of things as they were in the past. They are not ‘live’ images, they are not representation of these objects or events in what we call the present or ‘now’. They are images of the past, of what was not of what is.
This tallies in nicely with what I was talking about a few paragraphs ago. When we look into the distance, we not only see how far away something is but also how old it could be. So if light from a star takes 4 billion years to reach us then when we look up the night sky and see that star, the image we see is four billion years old, it’s the image of the star as it was four billion years ago. Not only is the star far, far away from us but it’s also at least four billion years old. And so, the further away we look in space, the older the objects and events are. This concept is not so much relevant in our day to day activities for the simple reason that the distances we deal with are on a scale which is insignificant to the speed light. However when we deal with distances of astronomical proportions then this becomes relevant.
We, therefore, sit in this immense Universe drifting by calmly and nonchalantly amidst stars and galaxies. A speck we might be before the majesty of the Universe but on that speck we call the Earth, on that world of ours, we are special enough to have the capacity to be awed by this majesty, this beauty, to understand and appreciate the Universe and to dream about alien worlds. If we give up on our dreams to explore space and seek out new life then we give up on what it means to be us.