Can we alter the past?

Time travel is theoretically possible, new calculations show. Time travel is possible based on the laws of physics, according to new calculations from researchers at the University of Queensland. But time-travelers wouldn’t be able to alter the past in a measurable way, they say — the future would stay the same.

Can information be sent back in time?

A device capable of “telegraphing into the past” was later also called a “tachyonic antitelephone” by Gregory Benford et al. According to the current understanding of physics, no such faster-than-light transfer of information is actually possible.

Can time go backwards?

Most importantly, time always appears to run forward, never backwards. In other words, there is a perceived arrow of time, and there is a thermodynamic arrow of time, and they both always point in the forward direction.

Which way is information?

The effect of “which-way” information measurement is the cornerstone of the Copenhagen interpretation of quantum mechanics. According to this philosophy, the state of a system is described by its probability wavefunction and lacks definite position or momentum until a measurement is performed.

How does a quantum eraser work?

They end up in an area called a quantum eraser with detectors 1&2, two mirrors, and another beam splitter. All you have to know is that it mixes up the photons so if detector 1 or 2 activates instead of 3 or 4 the which-way information is lost. As expected in the experiment the screen displayed an interference pattern.

Do you miss the “delayed-choice quantum eraser?

Most were small and nobody will really miss them, but I did feel bad about eliminating my discussion of the “ delayed-choice quantum eraser ,” an experiment that has caused no end of confusion. So here it is, presented in full. It’s a bit too technical for the book, I don’t know what I was thinking!

What is the difference between observation and measurement in quantum mechanics?

Observation and measurement are used interchangeably but a conscious observer is NOT required for this. Let’s not get into a pseudoscientific quantum consciousness rabbit hole. Measurement means that information about the particle is now available in the universe. Any physical interaction that makes this information counts as a measurement.

Can time be measured in quantum theory?

No. Time in quantum theory goes forward, like Newtonian absolute time. But one thing is time, the other one measurment of time. There is no operator for time measurement in quantum theory. In this sense, time is not measurable. Ok, it can be measured approximately, with clocks.