Monday, May 12, 2014

Time

 Time
     Some thoughts prompted by an article in New Scientist (http://www.newscientist.com/article/mg22029410.900-saving-time-physics-killed-it-do-we-need-it-back.html)
     Apparently one of the unsolved problems in the Standard Model of physics is time. Time is not privileged: the arrow of time could run either way. The only obstacle to running time backwards appears to be probability, or the 2nd law of thermodynamics. It’s more or less improbable for a system to decrease its entropy; and local systems can decrease entropy only with the addition of energy, which is scavenged from outside the system and therefore increases entropy elsewhere. The overall entropy of the Universe is increasing: and that’s why the arrow of time runs forward.
     But time does not “emerge” from the fundamental laws of nature as now understood. Worse, there are paradoxes and inconsistencies.
     In relativity, time is tangled with space, and worse, there are no fixed, absolute times for events: the times, and hence the sequence of events, depends on who is observing what. That puts paid to the arrow of time in a thoroughgoing way. It’s true that for any given observer entropy increases in the expected direction. But the observed sequence of events will be different for two observers moving relative to each other. That implies that one observer will place an event in the past, and another in the future. And that causes problems.
     In quantum physics (if I get this right), the future is uncertain. Until there is an interaction, certain states of a particle are indeterminate. The technical term for this is superposition; and when the interaction that determines the state of the particle occurs, the wave function that describes it is said to collapse. But the wave function may also collapse randomly, with no apparent interaction. There is only a series of state changes, and it’s this series that determines the sequence of what we observe as events. This means that the future is fundamentally indeterminate. Worse, entanglement seems to delay events, such as acquiring spin. Couple this with relativity, and we get a paradox: the acquisition of spin will be determined from one point of view, and undetermined from another.
     The usual notion of time is that the past is fixed because it’s already happened, and the future is undetermined because it hasn’t happened yet. Both relativity and quantum physics undermine this notion. In both, time is a derived property. We experience time as a sequence of events, that is, a series of changes. In fact, we measure the passing of time by observing a series of events, such as the oscillations of a pendulum, or the burning of candle, or the vibrations of a quartz crystal.
     So what’s to be done to rescue the notion of time? Some physicists are working on tweaking the mathematics of the Standard Model in various ways so that time is an absolute, independent property of the Universe. As an outsider with only a metaphorical grasp of the Standard Model, I notice two things: First, in relativity, the observed difference in a sequence of events occurs only when those events are independent of each other. But when events are a causal sequence, such as the oscillations of a pendulum, it’s the intervals between events that varies for different observers, not the actual sequence. Second, in quantum physics, I notice a fixed sequence of events. Entangled particles may be in a superposed position until they interact with some other particle (such as the one placed in the path of one of them by the observer). Then their wave function collapses. But that wave function collapse always follows that interaction, it never precedes it. In other words, wave function collapse implies a temporal sequence, no matter how far apart. I also note that the random interactions that all particles undergo cause changes in state in fixed sequences. If an electron is in a given spin state, it may flip to the other. In fact, we know of spin states only because we have observed that sequence. So those observations that undermine the notion of time can occur only because we observe events in sequence, in time.
     Time is fundamental in some way that the Standard Model can’t account for. Either the Standard Model is the best we’ll ever do, in which case the mystery of time will never be solved; or else the Standard Model will be superseded. We do live in interesting times, don’t we?

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