Time Is

[Music] [Applause] [Music] hello [Music] yes [Music] man conceived time [Music] since then he is trying to understand what it was he created [Music] or the most abstract of his ideas it comes from the simplest of his experiences events succession motion change cause and effect he cannot free himself from time and yet his personal experience of it is an anarchy firstly his perception of time is very limited most aspects of the time scale are beyond his senses he cannot see the mechanism of many ordinary events [Music] hmm [Music] hmm [Music] even that small part of the time spectrum he can grasp is elusive and inconstant [Music] in the summer time hangs slightly across the days [Music] um [Music] at other moments time can seem to stop altogether or utterly lose its meaning [Applause] we continually experience events which apparently change the rate at which time pulses some actions can make the passage of time seem slow and others can make it seem fast [Music] thank you [Music] god [Music] ah [Music] for us time is split into three the present the past which we know only through memory and the future which all men seek to know somewhere a mother must have asked what will my little boy become what will he do what will he say [Music] britain has been great is great and will stay great provided we close our ranks and get on with the job even the present we do not perceive as a moving instant but in lumps of now controlled by attention or association [Applause] [Applause] at the moment of catastrophe time can stretch into vivid in irradicable detail [Music] so when men speak about time it seems to mean a different thing to each of them [Music] although subjective judgments of time are undependable most animals have some form of built-in biological clock these are often true solar clocks and not governed by weather or geography these ducks are obviously returning from migration at the summons of a clock time and not a weather time [Music] [Music] in man the nearest approach to a biological clock is the alpha rhythm of his brain this lies between 8 and 13 cycles per second and is the dominant brain rhythm this alpha rhythm becomes manifest if the brain is stimulated at the same frequency this effect can sometimes be accidentally induced when driving at speed past a long row of trees which cross a low sun [Applause] [Music] as this 12-cycle flicker strikes the closed eyelids it produces in the mind brilliant colors and patterns dream images fabricated by the brain [Music] perhaps it is this rhythm which enables a man in perfect quiet to guess time intervals with uncanny accuracy but if he is isolated for a long time in pitch darkness his clock begins to run slow if he is spun in a centrifuge however his clock then runs fast the biological clock is governed by chemical processes and so it is affected by temperature and other factors on the left the nitric acid is cold and on the right it is hot the hot clock ticks faster animals whose bodies are kept at a very high temperature die sooner and in old age the body clock slows down and external time seems to go faster to every sportsman there inevitably comes a time to retire [Music] oh uh [Music] [Applause] so [Music] [Music] the biological clock too is fickle and unreliable [Music] men have always tried to make time an objective quality which they could measure and talk about consistently they built machines to contain it clocks [Music] [Applause] [Music] foreign [Music] huh [Music] and now they have a clock that loses only one second in 4 000 years [Music] but still they are unsatisfied still they ask what actually is thai does it only exist with events or in our minds is it the same everywhere and at all times perhaps to some other part of the universe we could look like this [Music] to the greek philosophers time was associated with motion time was the measure of motion just as number was the measure of quantity they argued that time was either continuous that is divisible without limit or was made up of discrete minimum units but zeno of alaya argued that in neither case could time exist because motion itself was impossible the javelinist seems to move but it is impossible that he can move first suppose the time can be divided without limit before he can reach the end of his run he must reach the mid point of it and before he can get that far he must reach the midpoint of that first half before he can reach even that point he must reach the midpoint before it and before he can reach that he must and so on ad infinitum to move from any one point to another he must travel through an infinite number of positions in a finite time motion is therefore impossible or suppose that time has indivisible units then motion must consist of a sequence of instance in each of which the objects are at rest but if they are stationary at each separate instant how then can they be moving over the whole interval ah [Music] [Applause] [Music] [Applause] [Music] the theory of relativity starts from difficulties about the idea of simultaneity that is about comparing times at different places to know of an event the information must be brought to us by a signal sound light messenger each travels at only a certain speed and therefore takes time this start looks simultaneous only because the speed of sound is much faster than our sensors slow the speed of sound down to our level say five miles an hour and the simultaneous start begins to look rather unsatisfactory try again with the starter moving but relativity theory brought with it some even stranger paradoxes suppose the speed of light is 60 miles per hour this young man parts from his friend and sets off around the universe at nearly the speed of light [Music] einstein says that his clock will run very much slower than his friend's clock when he returns after what was for him a short trip a hundred years have passed for his friend who is by now losing interest if he could accelerate right up to the speed of light our eternity would pass him in a flash [Music] [Applause] [Music] [Applause] [Music] the fastest way we can get information about something is by receiving light from it if it could travel away from us faster than the speed of light it would disappear its light could not reach us similarly if we travel away from it these ideas have been taken up by cosmologists who ask about the origin of the entire universe was it created and time itself in some gigantic explosion at some definite point of the past or did time exist before this a pre-cosmic time in an eventless matterless void has the universe always existed what is it trapped in a perpetual cycle [Music] again we always think of time as going in one direction [Music] is this a genuine property of time or only another of our human limitations [Music] life in reverse time seems ludicrous but in subatomic physics the idea is less bizarre consider the man to be an electron and the girl to be the unstable flighty positron the bubble cars are gamma ray photons a gamma ray photon can split spontaneously into an electron and a positron in a world consisting largely of electrons the positron is very nubile and is quickly snapped up by another electron and they turn back into another gamma ray photon mathematically this whole event is equivalent to a single electron bouncing forwards and backwards in time that is electrons going backwards in time are equivalent to positrons going forwards in time [Music] if therefore there is some part of the universe made of antimatter its time might seem to us to be flowing backwards [Music] if we rush to meet an antimatter time reversed person from such a world not only would communication be difficult but the actual meeting would rid us of everyone concerned [Applause] in relativistic quantum mechanics time can be regarded as atomic the smallest measurable time units being called chronons for durations less than the cronon past present and future cannot be distinguished within the cronon time order is arbitrary an ironic phrase about the one understood of my remark perhaps even implausible oppression that noah said nothing again i had the input i was the odd words passed over me as if i didn't exist and now some scientists are even playing with two-dimensional time [Music] with changes in the concept of time fantastic incredible worlds emergency [Music] [Music] that's right [Music] when man creates an abstract idea he creates a monster [Music] so [Music] you