Can time travel backward?

Does our reality exist if we are not observing it? Can time travel backward? These seemingly absurd questions derive from two incredible experiments that beg such questions.

The first experiment is of course the famous Double Slit Experiment which was first performed back as far as 1801 and repeated in the 1920s with electrons. The results have baffled Physicists for a hundred years. The other experiment was performed only a few weeks ago and the results are even weirder. Essentially the results of these two experiments challenge our logical understanding of time and Newton physics. It seems that reality as we know it does not actually exist until it is observed or measured.

The Double Slit Experiment

The Double Slit Experiment has been performed many times and the results are always the same. Let’s say you fire normal marbles through a plate with a single slit and toward a back wall. The result is an impression left in the back wall similar to the shape if the slit in the plate the marbles passed through. You get the same result when you fire electrons and protons into a similar setup at Quantum level. However, when you repeat the same experiment but with two slits in the plate, the marbles leave two impressions in the back wall with similar shape to the slits as you would expect. But do this same experiment with light particles, namely electrons or protons and you get multiple impressions or what is known to Physicists as an interference pattern. Even when they are fired through one at a time, to rule out that the electrons were bouncing of each other, the result is still an interference pattern.

This result is weird and counterintuitive because Physicists know full well that an interference pattern suggests they went through the slits as waves instead of particles. The interference pattern is exactly what you get when water goes through the two slits. Waves interfere with each other and cause peaks and troughs as well as cancelling each other out. The resulting pattern leaves multiple lines of impressions on the back plate where the waves exert the most pressure and between the lines there is little or no pressure because the waves have cancelled each other out.

If this was not weird enough, scientists decided to take a peek and see which slit the electrons actually went through. Upon observation, these particles left two impressions in the back plate instead of the multiple lines of the interference pattern. So why the different result? When you are not measuring or looking, protons and electrons act as waves, and when you take a peek, they behave as particles. To better understand the Double Slit Experiment, watch this video:

Wheeler’s Delayed Choice Experiment

Years later this experiment was repeated, but with the measuring device placed after the double slits. This would mean that the electrons should act exactly the same as if there was no measuring device because the electrons would enter the slits without being measured or observed. So what was the result? The experiment left two lines like the first experiment with the measuring device before the double slits. So it seems to make no difference where you place the measuring device or when you observe, because the result is the same. Measurement or observation before or after the plate with double slits gives the same result. It is as if the electrons should have gone through as waves, but then realised they were being observed, so went back in time and changed back to particles and then went through the slits as particles.

This and other experiments were thought experiments first proposed by John Archibald Wheeler. Called ‘Wheeler’s Delayed Choice Experiment’, the outcome has led many to question reality and time and to ask what they really are. They are best explained by this quote from George Greenstein and Arthur Zajonc, The Quantum Challenge, p. 37f.

These experiments are attempts to decide whether light somehow “senses” the experimental apparatus in the double-slit experiment it will travel through and adjusts its behavior to fit by assuming the appropriate determinate state for it, or whether light remains in an indeterminate state, neither wave nor particle, and responds to the “questions” asked of it by responding in either a wave-consistent manner or a particle-consistent manner depending on the experimental arrangements that ask these “questions.

Questions that naturally arise from the result of these experiments is whether time can go backward. There is nothing in mathematics that states it cannot. Another question is about reality itself. Does it only exist if we are observing it. In other words, does a tree fall in the forest if no one is there to observe it.

The latest experiment

A new experiment was then setup to further test the bizarre results of the Double Slit Experiment and Quantum weirdness. Using lasers and a helium atom instead of protons or electrons, an Australian team thought an atom might also exist in an indefinite state until observed, just like the smaller particles of protons and electrons. The lasers they used served as the slits in a plate or a grate with an initial grate, but the addition of a second grate that was used randomly.

What they discovered was just as weird as the Double Slit Experiment perhaps even stranger. When the two grates were used, the helium atom passed through in many paths like a wave, but when the second grate wasn’t present, the atom passed through the first like a particle. Of course the amazing thing about this is the fact that the second grate was random and the atom was effected before the second grate was used. In other words it hadn’t happened yet, but acted as if it had.

Does a helium atom know when there is going to be a second grate before it actually happens? It seems like it when we consider that the second grate is completely random and happens after the particle has already passed through the first grate. So it seems that its state as a particle or wave depended on something that happened in the future.

Can the future affect the past We are already familiar with the past and present affecting the future, but can time run backward too. Or is it that that the atoms did not travel, at all until they were measured or observed. If the atom really did take a certain path , then we would need to accept that a future measurement is affecting the atom’s past..

This adds to the bizarre questions that the Double Slit experiment has us asking. The questions are now justifiably a lot weirder than before.

If it is theoretically possible to travel back in time or to view time in reverse, then what exactly is happening at quantum level with experiments like the Double Slit experiment. One possible explanation is covered in a theory I call “The Theory of Conscious Time“. Another explanation is that things at quantum level are not subject to time because they are too small for time to act upon them. This would mean that time effects only collections of atoms but not individual atoms or particles themselves. If is correct, then where is the line that we cross before time is no longer relevant? Is there a time-line so to speak where one side has time and the other has no time? Perhaps the scale of a helium atom and no bigger? There will be more interesting experiments to come, yielding results that will hopefully get us closer to an explanation, but like many quantum based experiments, perhaps the results will only lead us to more questions.