When learning elementary physics, you are often amazed at how intuitive it is and how predictive it is. For example, the simple equations of kinematics are enough to calculate how long it will take for a solid ball thrown from a certain height to reach the ground. But, when studying the most complex parts of physics, sooner or later there comes a time when theories contradict intuition and become hard to believe.
Quantum mechanics is a good example. The fact that it is not possible to know, with total precision and at the same time, the position and speed of a body seems absurd. When a traffic radar takes a photo, the police know where the sanctioned car was and what exact speed it was going; It seems ridiculous to think that this is not the reality for all objects in the universe. However, this indeterminacy is well demonstrated with experiments.
The answer to that contradiction is that quantum effects are so tiny that, in everyday life, they are imperceptible . The inaccuracy in position or velocity due to quantum that could occur in an object as large as a car could become impossible to measure. Therefore, for physics to function as a predictive science in everyday life, it is not necessary to complicate life with the equations of quantum.
These failures of intuition are difficult to understand: they require knowledge of advanced physics to try to understand them. But there are very simple concepts that defy intuition for the sole reason that on the surface of the Earth they have no relevance. The fact that the speed of light is enormous, but finite, is one of them.
If we see a friend approach us on the street and, ten meters away, raise his hand, we will consider that the light coming from him reaches us instantly. But it is enough to use the most elementary physical equation, that speed is space divided by time, to verify that this is not true. It took our friend’s light 0.0334 millionths of a second to reach them. It is such a short time that it is out of reach, for example, of any stopwatch in common use, which does not distinguish beyond a hundredth of a second. So it is possible to disregard such short times and consider that the light comes to us instantaneously.
This is applicable to modern communications. Transmitting information over copper wires, fiber optics or satellite is done practically at the speed of light. For this reason, a phone call or an internet conversation between two people who live in Madrid and Rio de Janeiro, which are about 8134 km apart, takes place, according to our point of view, instantaneously: the transmission takes 0.027 seconds to arrive. to Brazil and many others to return. Priceless.
The problem is that it makes us believe that modern communications will always be instantaneous, because that is what we are used to. However, if we had a family member working on a lunar base, the transmission would take about 1.28 seconds to arrive (it could be a little more or a little less, since the Moon is not always at the same distance from Earth) . That means we would say “hello” and the response from our family member would reach us 2.5 seconds later. Slow and weird, but manageable.
The situation would get worse if our relative is on Mars. The minimum distance between the two planets is about 56.57 million kilometers, while the maximum is around 400 million kilometers. That implies that the light would take about 3 minutes and 9 seconds in the best case and about 22 minutes and 14 seconds when they are further away. A video conference or phone call is unfeasible when the response to a phrase takes between 6 and 44 minutes to arrive. If our unfortunate relative were on Pluto, it would take a little more than 5 and a half hours for the light to arrive, which means a response delay of about 11 hours.
Therefore, communication with people who are on other planets would be done through emails or sending video recordings, never in real time. Nor would it be possible to play online video games with friends who live on other planets. This is also why the rovers exploring Mars have artificial intelligence programs: if you had to give them all the orders from Earth, considerable time would be wasted just on the transmissions.
Despite this, in some science fiction films you see scenes like the following: a dramatic dialogue without delay between the crew of a ship with serious problems and the control center, despite the fact that the ship is hundreds of millions kilometers. Such a dialogue would be impossible, but we are so used to instantaneous communication with any place on Earth that we do not usually perceive this error.
The only reason we maintain the illusion of instantaneous communication is because Earth is actually a very small place, and human intuition only works when distances are at most a few thousand kilometers.
The good news is that physics doesn’t fail when human intuition does. This is why this beautiful science is such a powerful tool to help us understand the universe.
Juan Cuquejo mira, member of the cloister of the International University of La Rioja (UNIR).
