“Trying to understand the way nature works involves a most terrible test of human reasoning ability. It involves subtle trickery, beautiful tightropes of logic on which one has to walk in order not to make a mistake in predicting what will happen.” -Richard Feynman
If you were to send a space probe to a distant star system, gather information about it and send it back to Earth, you’d have to wait years for the information to arrive. But if you have an entangled quantum system — say, two photons, one with spin +1 and one with spin -1 — you could know the spin of the distant one instantly by measuring the spin of the one in your possession.
Are there prospects, then, for entangling quantum particles, placing one aboard a spacecraft and sending it to a distant star, making a measurement at that distant location and then making a measurement here to know what you saw over there? It’s an incredible idea to exploit quantum weirdness. While the laws of physics allow you to indeed know the properties of the other member of the pair by making a measurement here, they conspire to prevent you from transmitting information faster-than-light.