The Morning News How to grasp the insane dance that is quantum entanglement.

Here's the simplest explanation for what you're seeing that we could find:

When we measure both [entangled] members for color, or both members for shape, we find that the results always agree. Thus if we find that one is red, and later measure the color of the other, we will discover that it too is red, and so forth. On the other hand, if we measure the shape of one, and then the color of the other, there is no correlation. Thus if the first is square, the second is equally likely to be red or to be blue.

We will, according to quantum theory, get those results even if great distances separate the two systems, and the measurements are performed nearly simultaneously. The choice of measurement in one location appears to be affecting the state of the system in the other location. This “spooky action at a distance,” as Einstein called it, might seem to require transmission of information — in this case, information about what measurement was performed — at a rate faster than the speed of light.

But does it? Until I know the result you obtained, I don’t know what to expect. I gain useful information when I learn the result you’ve measured, not at the moment you measure it. And any message revealing the result you measured must be transmitted in some concrete physical way, slower (presumably) than the speed of light.

Upon deeper reflection, the paradox dissolves further. Indeed, let us consider again the state of the second system, given that the first has been measured to be red. If we choose to measure the second q-on’s color, we will surely get red. But as we discussed earlier, when introducing complementarity, if we choose to measure a q-on’s shape, when it is in the “red” state, we will have equal probability to find a square or a circle. Thus, far from introducing a paradox, the EPR outcome is logically forced. It is, in essence, simply a repackaging of complementarity.

### Researchers used ancient starlight to randomize an experiment, but still found quantum entanglement.

For decades, physicists contended that demonstrations of quantum entanglement were biased by observation. In an ingenious twist on an old experiment, researchers turned to ancient starlight from distant quasars to randomize the polarity of the particles used in the experiment. The results, however, stayed the same:

The colors of these photons were decided hundreds of years ago, when they left their stars, increasing the chance that they (and therefore the measurement settings) were independent of the states of the photons being measured. And yet, the scientists found that the measurement outcomes still violated Bell’s upper limit, boosting their confidence that the polarized photons in the experiment exhibit spooky action at a distance after all.

The experiment doesn't rule out an alternative entirely, but the primary exception would be a little bit spooky itself: determinism. If the state of the universe now is dependent on the state of the universe when the quasar emitted the photon used to randomize the experiment, that would also explain the results.

So we may have to pick between believing in a) a concept Einstein found so reprehensible he basically disowned it; b) a totally deterministic universe depends on the one before it; c) time travel.

Feb 16, 2017

In order to account for the results of our new experiment, the unknown mechanism would need to have been set in place before the emission of the starlight that Handsteiner’s group observed, back when Joan of Arc’s friends still called her Joanie.

Tangled up in q? Experimenters explain how they increased our certainty of quantum entanglement by a factor of "ten million billion."
↩︎ The New Yorker
Feb 16, 2017

### Quantum entanglement vexes us now. It might save us soon.

After all, with it we could...

—Build a better time capsule. You can use it to encrypt information that is impossible to decrypt until a specific moment in the future

—Sort large amounts of information quickly. And not just information, but atoms. Which means Star Trek replicators are on the horizon.

—Model chemical reactions as never before. Because molecules are highly entangled, understanding entanglement was the key to the first perfect simulation of a molecule.

Feb 16, 2017

Whether Trudeau rehearsed this as a stunt or not, it's actually kinda helpful.

Mathematically, entanglement in time is identical to entanglement in space, and we have no qualms with information traveling in all directions across space.

It's hard for us to fathom, but if you choose option c), time travel, then quantum physics actually starts to make sense.
↩︎ Quanta
Feb 16, 2017
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