Monthly Archives: October 2008

The Present

I run an astronomy course for homeschooled children of elementary and middle school ages.Last night’s session wasmy lecture entitled “Distance and Time”, dealing with the rather fascinating fact that in astronomy we are always observing events in the past. Although most educated adults “understand” this fact superficially, spending a couple hours talking about the ramifications of this fact as I expand the range that we’re discussing from the Moon (at about 1.25 light seconds from Earth) to the most distant objects observed by the Hubble Space Telescope (at about 13,000,000,000 light years from Earth) creates a lot of discussion in the class.

Last night, near the very end of the lecture, the youngest member of this class – age 8 I think – asked a very, very profound question. I had driven home the point repeatedly that everything we see happened in the past – even watching me across the room, the light they were seeing had left me a few nanoseconds before they “saw” it. His question (slightly paraphrased):

If everything we see and experience happened in the past, does the Present exist?

This question amazed me on several levels. In his actual phrasing of the question, it was clear to me that this was not an accidental stumbling upon a deep question – he really did have an inkling of what he was asking. The amount of experience he attempted to integrate in that instant was a huge surprise. I am still trying to follow how his mind could have created that question at such an early age.

I had no real hope of answering him in a manner he could understand, but that didn’t stop me from trying. Here is an expansion of what I told the class, in which I tried to explore the issue of observing very short time intervals. Although this was a somewhat technical answer (that no one in the room understood, perhaps including myself at the time), it has lead me further to consider just what the concept “Present” may actually represent.

Similar to how a computer functions, the human mind has a “clock rate”. Unlike a computer, which can perform billions of elementary calculations per second, the human brain’s neurons can fire at most 500 times a second.To receive and recognize visual information may require the firing of dozens of neurons, which brings our visual “frame rate” to maybe 10-50 frames per second. (This makes some sense, since a movie shot at 15 frames a second will appear visually “jerky”, while one shot at 30 or 60 frames per second generally looks smooth). For concreteness, let’s say the mind can receive one frame in 1/50th of a second. That means that anything happening in less than 1/50th of a second will be experienced as simultaneous.

Light travels at 186,000 miles per second. So, using our 1/50th second frame rate, anything that we observe within a range of about 3720 miles at a given instant in “global time” will appear to happen simultaneously. In some psychological sense then, our experience of “Now” has a range of 3720 miles.

As I said, this argument confused us all. And what I’ve written here is much clearer than what I said in the class last night – yet I’m still musing over what it means epistemologically, and what it means for our concept of Time.

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A comment about comments

There has been a dramatic increase in spam comments being posted to this blog – typically I’m getting 70 or so every month making it past whatever filter has been deployed by the blog’s host. In the past these have been easily dealt with – the content of the spam was obvious, and I could whip through the comments and typically delete all of them.

However, more recently the attacks have become more wily and sophisticated. The spam contains complete sentences, sometimes seeming to agree with a point from one of my posts. Only the broken English and finally the address reported for the commenter indicate that these comments are not legitimate, and I can still easily identify and delete them.

Now it is true that I have maybe 4 readers of this blog – including my wife – and in the three years this blog has been here I’ve gotten about 3 comments that were worth posting. So I could just say no comments allowed, and have those who want to comment just call me – or better yet, walk down the hall and see me – to register their opinions. But there’s an outside chance that someone I don’t actually know may land here and be interested enough to want to start a discussion, so I would prefer to keep comments open.

It is also true that other blog sites might have better systems, with better filters. Yes, that may be true, but they also push advertising in the reader’s face, and not all of it (more likely any of it) would I find joy in supporting. Here there is virtually no advertising, and the host is highly trusted to only insert links which I enthusiastically support. I could complain to the host about the system, but since he offers it for free, and does so for the best of all intentions, I can’t bring myself to whine about his service.

Ok – the point of this story

If you are going to post a comment, please follow these rules.

  1. If you do know me personally, drop me an email elsewhere telling me you’ve posted a comment (I do want your comment here so I can post it and refer to it in the future. If for some reason you don’t want your comment posted publicly, just say so in the comment).
  2. Start the comment itself with your full name, then a -:-, and the title of the post your commenting on. That should be unique enough that the spam jackals won’t be copying it soon.
  3. If you make a grammatical or spelling error, it is very likely I’lldelete your comment. It amazes me that the spam jackalshaven’tfigured this out, but there has almost never been a spam email or comment that I’ve read that didn’t contain an error.

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