Time is very simple, once you get it. But “getting it” is very very difficult. That’s because your current concept of time is so deeply ingrained. You think of time as a length: Q: How long will it take to get to London? A: What do you mean long? We form a mental map of the world using our senses and our brains. But the map is not the territory. We use time to think, but we’ve grown so accustomed to thinking the way we do, that we don't think about time any more. We don't see time for what it is. But let’s start with something easier. Let’s start with colour. Follow the link below to conduct an experiment: http://www.echalk.co.uk/amusements/OpticalIllusions/colourPerception/colourPerception.html This demonstrates something important about colour perception. What you thought was yellow is in fact grey. It really is. It isn’t a trick. Tear a small hole in a piece of paper to make your own mask to remove context. Hold it up to one image after the other, and you realise that the effect is genuine. It comes as a shock, but genuine it is. Yellow is grey. What does this tell you? It tells you that colour is perception rather than reality. Imagine a super-evolved alien bat with a large number of ears, like a fly’s eye. This bat would “see” using sound, and if it was sufficiently advanced it would see in colour. This should be a reminder that in the subatomic world there is no such thing as colour. A photon has a wavelength, an electromagnetic oscillation, a motion. Next let’s take a look at heat. Put your hand on the griddle and sizzle, you know heat is real. But we talk about heat exchangers and heat flow as if there’s some magical mysterious fluid in there. And yet we know there isn’t, because junior-level physics tells us that heat is atomic or molecular motion. It’s a “derived effect”, or a macro effect if you prefer. Sure, heat is a real thing. But you know it's motion. Pressure is similar. You can’t measure the pressure of an atom, because pressure isn’t a fundamental property of the sub-atomic world. It’s another ”derived effect”, and the Kinetic Theory of Gases tells us it’s derived from motion. How about Kinetic Energy? A cannonball in space travelling at 1000m/s has Kinetic Energy. Oh sorry. I made a mistake. It isn't the cannonball doing 1000m/s. It's me. So where's the kinetic energy now? Nowhere. Because it's just a mathematical expression of stopping distance. There isn't any. All there is is motion. We’re all familiar with Sound. It’s like light because it’s waves, and like pressure because they’re pressure waves. And when you look beyond this at the molecules that make up the air around us, you see that sound is motion. Please Register or Log in to view the hidden image! Did you know that smell is really shape? Look up Olfaction on wikipedia, but nevermind, because you should be getting the drift by now. We are accustomed to thinking about the world in terms of how we experience it, rather than the scientific, empirical, fundamental, underlying things that are there. And nowhere is this more so than with Time. What is Time? Let’s start by looking up the definition of a second: "Under the International System of Units, the second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom. This definition refers to a caesium atom at rest at a temperature of 0 K…” OK, a second is nine billion periods of radiation, of light. Now, what’s a period? We mentioned light, so let’s have a look at frequency: Frequency = 1 / T and Frequency = v / λ Flipping things around, I see that period T is wavelength λ divided by velocity v. A wavelength is a distance, a thing like a metre: “The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second...” And a velocity is a distance divided by a time. So: A period T is a distance divided by a distance divided by a time. That’s a another period, another time. OK, so that definition of time is circular. We can’t see the empirical fundamental definition. The axiom warning light is flashing, so let’s look at frequency again: "Frequency is the measurement of the number of times that a repeated event occurs per unit of time". And the penny drops. We measured nine billion oscillation events and then we defined that as a second. We counted events. We counted motions. That’s what time is. It’s counting. One two three four five… nine billion. Mark that down as a second. One two three four five… nine billion. Another second. And you don’t have to count the motion in an atomic clock. You could count the motion of beans in a a bucket. Ping, ping ping, chuck them in, regular as clockwork. But now you should notice something: the only direction that is actually there, is the direction of the beans' motion. "More beans" is not a direction. There is no direction for the “Arrow of Beans” to point to. It’s just a mathematical notion, as imaginary as the direction you take when you count along the set of integers. So why on earth do we say things like Clocks slow down as if a clock is something that moves like a car? It isn't travelling. There's no slow or fast or up or down to it. We say The day went quickly but it didn’t go anywhere, and it didn’t go quickly at any speed at all. It isn’t travelling and there is no direction. The only directions that are there are the directions of the internal cyclic motion. And they’re being counted, incremented, added up. We count this regular motion to use as a ratio against some other motion, be it of light, atoms, buses, or brains. All of these things have motion. Some have more of it than others. And all those motions are real, with real directions in space. But the time direction isn't real. It's as imaginary as that direction you take when you count along that set of integers. That's why the past is only in your head and your records. It's the places where things were. All those places are still here, now. It isn’t a place where you can go. The past is the sum of all nows, and now lasts for zero seconds because there is no fundamental time. Only motion. A second is nine billion motions of a caesium atom. Accelerate to half the speed of light and a second is still nine billion motions of a caesium atom. But there's only half the local motion there used to be, because the other half is already doing the motion through space. Look again at the definition of the second and the metre, and you will understand Special Relativity. Time didn’t begin fifteen billion years ago. Because it never started in the first place. It was motion that started in the first place. And it was fifteen billion light-years a go-go. Let’s go over it again. Imagine yourself as a metronome. Each tick is a thought in your head, a beat in your heart. If you’re travelling with a forward motion of c you can't tick, because any transverse motion would cause c to be exceeded. If however your forward velocity is zero you can tick with a transverse motion of c. Your time experience changes, but it merely depends on how your motion is cut. Motion is a change of place in space. We measure this by comparing it with some other motion, and use the term "time" in our measuring. It's a measure, so by definition it's a dimension in the proper sense. But that only makes it a parameter, not a spatial, linear dimension that we can move along. So why do we say how long when we're thinking about time? We imagine a length of time. We imagine that we travel along this imaginary length at a speed of one second per second. When you "get" time, you realise just how ridiculous this is. We don't travel anywhere in time. Our atoms and everything else are in motion, but there's no travelling through the measure of this motion. To travel backwards in time we'd need negative motion. Motion is motion whichever way it goes. You can’t have negative motion. So What do we do with SpaceTime? Ah, Einstein. He knew all right. He found his Hole. Einstein’s Hole. Look it up. Talking of Einstein, let’s look at Simultaneity, and a little thought experiment called the “Cylinder and the Nail”. The cylinder is the same length as the body of the nail. At the far end of the cylinder there's a sheet of paper stretched across it like a drumskin. If you were to slide the nail into the cylinder, the pointy end of the nail just touches the paper, but it doesn't penetrate because the head of the nail is too wide to fit into the cylinder. You mount collision detector A on the head end of the cylinder, and collision detector B on the paper end of the cylinder. Now with a very special gun, you can fire the nail at the cylinder, or the cylinder at the nail, and monitor your collision detectors. From the cylinder's perspective, the nail is a shortened spike. So the first detector to fire is A at the front end of the cylinder. The nail doesn't stop (in reality we're talking gamma-ray plasma jets here) so detector B at the paper end fires later. From the nail's perspective, the cylinder is a flattened doughnut. The first detector to fire is B at the paper end. Detector A at the front end of the cylinder fires later. From the cylinder's perspective A "happens before" B, whilst from the nail's perspective B "happens before" A. The time experience is therefore subjective to each object and its motion, and is not an objective experience independent of motion. Ergo our experience of time is a subjective experience that is the product of motion, and our treatment of time as a length and a travel direction is incorrect. The correct concept of time has to defer to velocity. Velocity is not distance over time. Instead velocity determines your measure of time and space, because spacetime is fundamental, not space, and not time. Velocity is motion, more absolute than distance, more absolute than time. We measure the motion of the molecules of a gas using temperature. There is no time in temperature. And while we talk of a “high temperature”, we cannot travel a “height of temperature”, because there is no height. And we cannot travel a “length of time”, because there is no length. I’ll show you a picture: Please Register or Log in to view the hidden image! What can you measure? OK you can measure height. And width. And if it wasn't just a picture you could also measure depth. That's three Dimensions, with a capital D because we can move in those dimensions. What else can I measure? What is the fourth dimension? Well, the picture comes from the Wikipedia Temperature page, so I can also measure the temperature. The motion. The velocity. It's a measure of change of place rather than a measure of place, and it has no absolute units, because you can only measure one change of place against another. It's a fourth dimension, but you can't move in this dimension so it's a dimension with a small d. And because there are no absolute units, the units are relative, which is what Special Relativity is trying to tell us. And Special Relativity is also trying to tell us something about the speed of light. Speed is distance over time. But light experiences no time, so talking about speed doesn’t make sense. Light doesn’t travel at any speed. It is a constant, because it is constant. And that constant c has its own units of velocity that we should liken to temperature. Velocity should be defined by degrees, not by metres and seconds, because it defines metres and seconds. And because it defines metres and seconds it but a short step from there to telling the children that the speed of light is the speed of time. Strange but true. Because when you get down to the subatomic nitty-gritty, there is no colour. There is no heat. There is no sound. There is no pressure. There is no time, not the way you think. Now try to imagine a particle, without a surface please. And you see why the quantum world, the real world of physics, is oh so very strange. If you don't believe me, if you think I'm wrong, show me the maths. But make sure you kick little old t out of all of your equations. And note that there are physicists who think like me. Julian Barbour. Carlo Rovelli. And more. Ever heard of a book called A World Without Time: The Forgotten Legacy of Godel and Einstein, by Palle Yourgrau? "It is a widely known but insufficiently appreciated fact that Albert Einstein and Kurt Goedel were best friends for the last decade and a half of Einstein's life. They walked home together from Princeton's Institute for Advanced Study every day; they shared ideas about physics, philosophy, politics, and the lost world of German-Austrian science in which they had grown up. What is not widely known is that in 1949 Goedel made a remarkable discovery: there exist possible worlds described by the theory of relativity in which time, as we ordinarily understand it, does not exist. He added a philosophical argument that demonstrates, by Goedel's lights, that as a consequence, time does not exist in our world either. If Goedel is right, Einstein has not just explained time; he has explained it away..." Time Travel is bunk. Sleep tight.