Feymann's QED theory requires the existence of positrons that come to the present from the future. So the causility that you speak of is not present in particle quantum mechanics.

For example, thake the double slit experiment. In Feymann's theory, whether the particle is detected at one slit or not is known from the anti-particle that comes back from the future. That amount of time is much more than what is allowed in the uncertainty principle. So the future in Feymann's theory is not just the uncertainty time as you once previously suggested.

Feymann's theory is thought to be the most accurate theory ever, and yet uses "time reversal" in its fundamental level. It does not allow time travel imto the past. But it clearly allows for time travel into the future if the particles doing the time travel are sufficiently close to the speed of light.

• No, it is ONLY within Heisenberg uncertanty time. - alexander - January 15, 2002 - 22:24 UTC
  • HERE IT IS!!! TIME TRAVEL - medvedbr - January 16, 2002 - 01:43 UTC
    • How about causality when reversing time? - alexander - January 16, 2002 - 04:05 UTC
      • no direction? - medvedbr - January 21, 2002 - 20:55 UTC
  • Double slit experiment cannot be explained by QED - yanniru - January 16, 2002 - 14:23 UTC