What is Time Anyway?
Spacetime: not space; not time; not space & time; not space-time. Spacetime. Got It?
If you want travel in time, it helps to know what spacetime is. HINT: you might be traveling in spacetime at the speed of light right now.
Spacetime is what Einstein’s teacher Minkowski called the universal frame of reference in which we are interwoven. In short everything. It is not “space” and “time,” although that is definitely the way most people think of it, so I’ll break some rules and start with . . .
Space. Most of the time it’s ok to regard up, down, east, west, north, and south as Space. Or x, y and z for those who prefer. Spoiler alert: space is not like a theater stage or basketball court with walls and fixed dimensions. Why not? Because it is spacetime and spacetime has its own set of rules and they are not the same for everyone. Also space as we know it extends from the very itty-bitty, way smaller than any sub-atomic particle to the boundless vacuum of the universe. (Comfort note: if you count the orders of magnitude from bottom to top in size, humans are about in the middle.) So, that brings us to . . .
Time. Newton made use of time in his calculations, however most scholars, Newton included, don’t claim to understand time at a fundamental level. For example: why do equations in physics which calculate just fine backward, fail to represent the reality of big stuff in reverse, whereas Feynman diagrams of the interaction of matter and energy, little stuff, correctly describe movements backward in time? Explanations involve equations, blackboards, hand-waving, and ultimately invoking entropy and quantum mechanics. I guess we have to go there.
Entropy. Mostly applies to big stuff.
The 1st Law of Thermodynamics: in an isolated system, “Work” can only be done by a difference in heat, you know, “thermometer.” No free energy from the air, sorry YouTube.
The 2nd Law of Thermodynamics’ central concept is that entropy, in an isolated system left to spontaneous evolution, cannot decrease over time. Don’t wear perfume to the gym or ride an elevator after lunch from Chipotle. You get the idea, right?
Life—meaning everything that will die at some point—has to constantly “work” to organize and reduce entropy.
Quantum Mechanics. Mostly applies to little stuff.
The Electron, without which we would literally fall through the floor. Electrons, you see, do not share their space. Ever. So when the electrons in your foot meet the electrons of the floor, they resist with all the energy they can muster. Electrons are so negative.
The Photon, the carrier of energy. Don’t make light of it; it IS light and all the spectrum from below AM radio, infrared, through the narrow range of our light vision, to x-rays and beyond. For doing all that for us, the photon gets a bonus: it never has to ask “Are we there yet?” Photons are always there. Time never passes for them and they travel at the speed of light (duh). Bad news is if a photon hits anything, they “give it up.” The cosmic background radiation everywhere in the universe comprises photons coming from the dawn of time, but with their energy shifted down to nearly absolute zero. How cool is that?
The Proton, they get to determine, by their numbers, exactly which element they constitute. Hydrogen—the most abundant element in the universe—has only one proton, still it remains positive. Two protons: helium after ‘helios’ the sun, where helium was first discovered. The proton has a sidekick . . .
The Neutron, remains neutral on most subjects, mostly because there is no ‘charge’ but also due to its secret of being able to turn into a proton and an electron as a clever party trick called ‘beta-decay’. Too much fun!
Any more? Well, the electron and the photon are ‘elementary particles’ of which there are seventeen, most recently joined by the elusive, but very much sought after ‘Higgs Boson’. The only ones we need worry about are the UP quark and the DOWN quark as these—along with their energy particle the ‘gluon’—constitute all everyday matter by way of being the inner clockwork of both the proton and the neutron. Whew!
Wait, wait; what about the force of gravity? There has to be particle for that force, right?