have the opposite effects but probably would be as deadly: you’d weigh less; birds would soar higher than ever before; the sun would cool off as it bloated, and we’d freeze to death. Of course, in Dicke’s theory the decrease is imperceptibly slow: maybe as much as a 1 percent decrease in a billion years. Even that slight change might be detectable in highly precise measurements of planetary motion and perhaps in geophysical effects. Attempts to find evidence of a change in the gravitational constant have so far failed.
Variations
Poincaré’s thought experiment, which helped pave the way for the acceptance of Einstein’s relativity, illustrates one of the mostpalatable forms of antirealism. Many variations on Poincaré’s fantasy are possible. Obviously, a nocturnal shrinking of the universe would be equally undetectable. Would there be any way of telling if:
• The universe “stretched” to twice its size in one direction only (and things that changed their orientation after the change stretched or compressed proportionately)?
• The universe turned upside down?
• The universe became a mirror image of itself?
• Everything in the universe doubled in value, including money, precious metals, and whatever is used for currency on other planets?
• Time started running twice as fast?
• Time started running twice as slow?
• Time started running a trillion times slower?
• Time stopped completely, starting right … NOW!
• Time started running backward?
Most would say that all these scenarios would be equally undetectable and meaningless. The last two questions in the list deserve comment.
You could never know it if time stopped. You
can
know that it didn’t stop last night or three seconds ago when you read the word “NOW!” (I speak of time stopping “forever,” and not just stopping for a “while” and then starting back up again. A temporary suspension of time would be undetectable.) Whether this very moment is the moment in which time stops is something you cannot know until after the fact.
If you are sure that time is
not
running backward, ask yourself how you know this. You probably cite your memories of the past. It is now 1988. You have memories of experiences in 1987, 1986, 1985, etc.; you do not have memories of 1989, 1990, etc. But you would, for the moment, have the memories you do whether time was going forward or backward from 1988. The question is whether the moving finger of time adds to or deletes from this stock of memories. There is no way of telling!
Did Time Begin Five Minutes Ago?
The best-known thought experiment about time was devised by Bertrand Russell in 1921 (or was it?). Suppose that the world was created five minutes ago. All memories and other traces of “prior” events were likewise created five minutes ago as a private joke onthe Creator’s part. How do you prove otherwise? You can’t, Russell insisted.
Few would argue with Russell, for the same reasoning quashes any proposed refutation. A 1945 bottle of Château Latour—the yellowed pages of a Gutenberg Bible, dated 1457—fossils—carbon 14 dating—astrophysical evidence of the age of stars—the Hubble time—none means anything more than the time on a clock in a painting. They were simply created that way, five minutes ago.
(In a weird case of theology imitating philosophy, some opponents of Darwinian evolution have claimed that God created fossils to tempt the wicked into disbelieving that the world was created in 4004 B.C., as Archbishop Ussher figured in the margins of the King James Bible.)
Perils of Antirealism
The antirealist position can be applied unwisely. There is always the danger of assuming too readily that something presently unknowable must remain so forever. In 1835 French philosopher and mathematician Auguste Comte, founder of logical positivism, advanced the chemical composition of stars as something necessarily beyond human knowledge. “The field of positive philosophy
Variations
Poincaré’s thought experiment, which helped pave the way for the acceptance of Einstein’s relativity, illustrates one of the mostpalatable forms of antirealism. Many variations on Poincaré’s fantasy are possible. Obviously, a nocturnal shrinking of the universe would be equally undetectable. Would there be any way of telling if:
• The universe “stretched” to twice its size in one direction only (and things that changed their orientation after the change stretched or compressed proportionately)?
• The universe turned upside down?
• The universe became a mirror image of itself?
• Everything in the universe doubled in value, including money, precious metals, and whatever is used for currency on other planets?
• Time started running twice as fast?
• Time started running twice as slow?
• Time started running a trillion times slower?
• Time stopped completely, starting right … NOW!
• Time started running backward?
Most would say that all these scenarios would be equally undetectable and meaningless. The last two questions in the list deserve comment.
You could never know it if time stopped. You
can
know that it didn’t stop last night or three seconds ago when you read the word “NOW!” (I speak of time stopping “forever,” and not just stopping for a “while” and then starting back up again. A temporary suspension of time would be undetectable.) Whether this very moment is the moment in which time stops is something you cannot know until after the fact.
If you are sure that time is
not
running backward, ask yourself how you know this. You probably cite your memories of the past. It is now 1988. You have memories of experiences in 1987, 1986, 1985, etc.; you do not have memories of 1989, 1990, etc. But you would, for the moment, have the memories you do whether time was going forward or backward from 1988. The question is whether the moving finger of time adds to or deletes from this stock of memories. There is no way of telling!
Did Time Begin Five Minutes Ago?
The best-known thought experiment about time was devised by Bertrand Russell in 1921 (or was it?). Suppose that the world was created five minutes ago. All memories and other traces of “prior” events were likewise created five minutes ago as a private joke onthe Creator’s part. How do you prove otherwise? You can’t, Russell insisted.
Few would argue with Russell, for the same reasoning quashes any proposed refutation. A 1945 bottle of Château Latour—the yellowed pages of a Gutenberg Bible, dated 1457—fossils—carbon 14 dating—astrophysical evidence of the age of stars—the Hubble time—none means anything more than the time on a clock in a painting. They were simply created that way, five minutes ago.
(In a weird case of theology imitating philosophy, some opponents of Darwinian evolution have claimed that God created fossils to tempt the wicked into disbelieving that the world was created in 4004 B.C., as Archbishop Ussher figured in the margins of the King James Bible.)
Perils of Antirealism
The antirealist position can be applied unwisely. There is always the danger of assuming too readily that something presently unknowable must remain so forever. In 1835 French philosopher and mathematician Auguste Comte, founder of logical positivism, advanced the chemical composition of stars as something necessarily beyond human knowledge. “The field of positive philosophy
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