One of the tasks of philosophy is to expose bad philosophy. Scientists pump out quite a lot of it. Physicists are among the worst. I have given many examples. Here is another one. Let's get to work. Dartmouth physicist Marcelo Gleiser writes in There is No Now,
You say, “I’m reading this word now.” In reality, you aren’t. Since light travels at a finite speed, it takes time for it to bounce from the book to your eye. When you see a word, you are seeing it as it looked some time in the past. To be precise, if you are holding the book at one foot from your eye, the light travel time from the book to your eye is about one nanosecond, or one billionth of a second. The same with every object you see or person you talk to. Take a look around. You may think that you are seeing all these objects at once, or “now,” even if they are at different distances from you. But you really aren’t, as light bouncing from each one of them will take a different time to catch your eye. The brain integrates the different sources of visual information, and since the differences in arrival time are much smaller than what your eyes can discern and your brain process, you don’t see a difference. The “present”—the sum total of the sensorial input we say is happening “now”—is nothing but a convincing illusion.
Gleiser is confusing seeing with object seen. True, light travels at a finite speed. So the word seen is the word as it was one nanosecond ago. But it doesn't follow that I am not seeing the word now. The seeing occurs now at time t, the word seen, however, is not the word as it is at t, but the word as it was at t* (t*<t).
When I glance at the sun, I see it as it was about eight minutes ago. But it does not follow that the seeing (glancing) is not occurring now, or that there is no now.
Suppose that at time t I am visually aware of a word and of a cat. I am focused on the word, but the cat is nearby in the periphery of my visual field. So the seeing of the word and the seeing of the cat are simultaneous seeings. But the word I see is the word as it was one nanosecond ago, whereas the cat I see is the cat as it was, say, 10 nanoseconds ago. So I grant that there are a couple of illusions here.
The first illusion is that if a seeing occurs at time t, then the object seen is as it is at t. This cannot be given the well-known facts that Gleiser adduces. The object seen is as it was at an earlier time t*. But if you see through (forgive the pun) the first illusion, you may still succumb to the second. The second illusion is that objects seen at the same time t are as they were at the same time t*, where t* is earlier than t. In my example, the seeing of the word and the seeing of the cat occur at the same time, call it t. But, given that word and cat are at different distances from the subject, there is no one time t*, earlier than t, such that word and cat were as they were when they were seen.
But again, that does not show that the present moment or the Now is an illusion.
Gleiser's thesis is that there is no Now, that it is a "cognitive illusion." He sums up:
To summarize: given that the speed of light is fast but finite, information from any object takes time to hit us, even if the time is tiny. We never see something as it is “now.” However, the brain takes time to process information and can’t distinguish (or time-order) two events that happen sufficiently close to one another. The fact that we see many things happening now is an illusion, a blurring of time perception.
Gleiser is just confused. There is an illusion, but it is the illusion that we see things as they are now. But that is not to say that there is no Now, or that the Now is an illusion. In fact, Gleiser presupposes that there is a Now when he says that we never see anything as it is now. Right now the Sun is in some definite state, but the physics of visual perception make it impossible to see the Sun as it is now. If it had gone supernova three minutes ago, it would appear to us now as it usually does.
Geiser confuses an epistemological claim -- We never see anything distant from us as it is at the precise time of the seeing -- with an ontological claim: there is no present moment.
There is other nonsense in Gleiser's piece. Take this sentence: "The notion of time is related to change, and the passage of time is simply a tool to track change." I'll leave it to the reader to sort this out. I've had enough!
Related entries:
Why Do Some Physicists Talk Nonsense about Nothing?
"We're Just a Bit of Pollution," Cosmologist Says
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