The wave—particle duality of quantum mechanics dictates that all quantum objects, massive or otherwise, can behave as either waves or particles. The helium atoms, released one by one from an optical dipole trap, fell under gravity until they were hit by a laser pulse, which deflected them into an equal superposition of two momentum states travelling in different directions with an adjustable phase difference. The researchers then decide whether to apply a second laser pulse to recombine the two states and create mixed states — one formed by adding the two waves and one formed by subtracting them — by using a quantum random-number generator.
When applied, this final laser pulse made it impossible to tell which of the two paths the photon had travelled along.
The team ran the experiment repeatedly, varying the phase difference between the paths. However, application of the second pulse produced a distinct sine-wave interference pattern. When the waves were perfectly in phase on arrival at the beamsplitter, they interfered constructively, always entering the state formed by adding them.
When the waves were in antiphase, however, they interfered destructively and were always found in the state formed by subtracting them. This means that accepting our classical intuition about particles travelling well-defined paths would indeed force us into accepting backward causation. The other less likely option would be that of backward causation — that the particle somehow has information from the future — but this involves sending a message faster than light, which is forbidden by the rules of relativity.
Aspect is impressed. The research is published in Nature Physics. Close search menu Submit search Type to search. Topics Astronomy and space Atomic and molecular Biophysics and bioengineering Condensed matter Culture, history and society Environment and energy Instrumentation and measurement Materials Mathematics and computation Medical physics Optics and photonics Particle and nuclear Quantum. Sign in Register. What's more, you could calculate the velocity of the stool after you hit it with the ball, but you have no idea what its velocity was before you hit it.
To know the velocity of a quark we must measure it, and to measure it, we are forced to affect it. The same goes for observing an object's position. Uncertainty about an object's position and velocity makes it difficult for a physicist to determine much about the object.
Of course, physicists aren't exactly throwing medicine balls at quanta to measure them, but even the slightest interference can cause the incredibly small particles to behave differently. This is why quantum physicists are forced to create thought experiments based on the observations from the real experiments conducted at the quantum level.
These thought experiments are meant to prove or disprove interpretations -- explanations for the whole of quantum theory. In the next section, we'll look at the basis for quantum suicide -- the Many-Worlds interpretation of quantum mechanics.
Sign up for our Newsletter! Mobile Newsletter banner close. Mobile Newsletter chat close. Mobile Newsletter chat dots. It goes as follows:. You can say where the stool was, but not where it is now. When we start working with very small amounts of energy, we notice a problem: light, the means by which we observe most things, is itself powerful enough to completely change what is going on.
So light would be the medicine ball in the analogy. It is energetic enough to cause significant changes on a quantum scale. Any attempt to measure something on the quantum scale will invariably result in altering what you were trying to measure at the start. So in short, the equipment we use is perfectly capable of distorting our results, but we can expect a baseline of error simply by observing it in the first place.
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