# How relativity really works in real life

In the development of GPS (Global Positioning System) satellites, scholars discovered that: according to Einstein's special theory of relativity published in 1905, atomic clocks on satellites would be 7 microseconds slower than those on the ground every day due to the speed of motion; and according to the general theory of relativity published in 1916, atomic clocks on satellites would be 45 microseconds faster than those on the ground every day due to different positions in the gravitational field microseconds. Combining the two, the atomic clocks on GPS satellites will be 38 microseconds faster than those on the ground per day. If the time is not calibrated, the positioning position will drift by a distance of about 10 km per day.

Without relativity, there would be no GPS. So standing in 1905 or 1916, can one imagine that relativity theory can be of any use? Standing in 1854, I am afraid one could not imagine Riemannian geometry could be of any use either. Even in 1978, the U.S. developed GPS for the purpose of positioning its own missiles and nuclear submarines, etc. In 1983, Korean Air Flight 007 was shot down in Soviet airspace by mistake, and then U.S. President Reagan announced that GPS would be opened to the public to prevent similar tragedies from happening again. 1989, the first new generation of GPS satellites was successfully launched, and in 1994, all 24 GPS satellites were put into orbit. All 24 GPS satellites were put into orbit. The satellite navigation we need to drive today was not even imagined by science fiction writers in 1905.

Today, when we say to our cell phones "find me the best rated restaurant nearby", how much pure theory is involved behind it? Calculus, Riemannian geometry, complex functions, probability theory, relativity, electricity, optics, organic chemistry, inorganic chemistry ...... each theory, when it was born, we did not expect its role in daily life.

In a word, science and engineering are different. The purpose of science is to explore the laws of the world, while how these laws should be applied is the business of engineering. The main job of engineering is to use the theories and laws discovered by science to solve the problems that need to be solved in human society (of course, engineering develops a lot of understanding of the laws of the world in the process). The usefulness of the results of science will rarely be as obvious as that of engineering. Science is supposed to be ahead of its time. It is because research in science is always difficult and slow that we should persistently invest in expanding the boundaries of human cognition. If engineering finds that the theory of science cannot support the actual problem, and then invests money in science to study the related problems, the solution of the problem will be delayed for decades, which will greatly hinder the progress of human society.

If we are going to solve existing problems with existing theories, then we need to make sure that science research is ahead of society as a whole. Thus, the first applications of today's cutting-edge science research results are often decades or even centuries away, and its applications are likely to take forms that we can hardly imagine now.

It is often questioned that there are still many poor people in the world, so why not subsidize them with money instead of doing some scientific theoretical research that currently has no application scenarios in sight? This is because the main force that raises the standard of living is the increase in the level of productivity. If we still maintain the same level of productivity today as we did a thousand years ago, then no matter how much we help the poor, everyone's life will not be any better. Strengthening research in basic disciplines is beneficial to society as a whole, even if we do not see application scenarios for the time being. What do you think about this?