|MadSci Network: Physics|
My, that’s quite a question. I’ll split your question up into two parts: 1) what is the ‘present’ for our subjective experience, and 2) what is the ‘present’ from an objective perspective. Subjective ‘Present’: I was reading Penrose’s “The Emperor’s New Mind” the other day. Turns out it has a chapter that goes to the heart of some of your questions about the order in which the brain processes signals. First of all, it confirms your suspicions about the processing time necessary to interpret stimuli. Your perspective of the present is actually several milliseconds delayed in ‘real’ time. However, the brain also interleaves different signals in different ways. You can react to certain stimuli (touching a hot stove) much more quickly, so there are some signals that you can process before you’re even aware of them. There were also experiments described in which carefully chosen stimuli occurred in one order, but were perceived in reverse order, and then vice versa. Therefore, I would conclude that our perception of the ‘present’ is garbled to the point where it really serves no meaning except to describe your current state of consciousness. Furthermore, I would argue that my perception of the ‘present’ has only a tenuous relationship with anyone else’s perception of the ‘present.’ [Roger Penrose, “The Emperor’s New Mind: Concerning Computers, Minds, and the Laws of Physics” (Oxford Press, 1999, ISBN 0192861980). I cannot remember details, but the experiments I’m talking about are described in his chapter on the structure and operation of the brain, and he includes full reference information there.] Objective ‘Present’: As for an objective version of the ‘present,’ this too is tricky. As you hinted in your question, this goes beyond physics into philosophy or semantics. Whether a person can point to the existence of a ‘present’ is going to depend entirely on how that person defines the concept. Whether anyone else will believe the argument will depend first on whether the concept was communicated clearly enough, and then whether they believe the definition, too. Extemporaneously, I’ll present an argument for an objective ‘present’ in a local sense, based on the ideas of physics. Arguing from a physics perspective, however, does not necessarily mean that the arguments would be accepted universally. It’s merely the most comfortable framework for me. (Note also that this description is filled with just as much jargon as would be required of a philosopher – “inertial reference frame” and “relativity” are phrases that require an awful lot of background baggage before they can be appreciated, just as do technical terms from epistemology.) Provided we do not approach a gravitational singularity, any event in space can be labeled with a local position and local time. Furthermore, physics tell us the order of events which take place in the same location will always be the same: if one person sees A before B, then everyone else will see A before B (if A and B occur in the same spot in our local inertial frame). Relativity says that time and space _between_ events are different for different observers, but that the order in which they occur is always observed to be the same. Furthermore, we can trace the flow of events down to very, very small increments. Near as we’ve been able to measure, time is continuous. So, I argue for a ‘local present’ in the following way. As we record events with ever-smaller increments and ever-faster speeds, the ‘present’ is the limit of the sequence of past events. I think you’re right in that we cannot ever experience the present, as both measuring devices as well as our brains take time to record events, but I think one can define a present as this limit. Interesting question – it certainly made me think, - Guy
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