The Biggest Unanswered Questions In Physics Today

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Physics mysteries are everywhere we look. From the nature of reality to why the shower curtains blow in, there is so much that we don’t know. And while ignorance is part of the human experience, so is knowing things. We are also bothered when people (or in this case nature) keep things from us. Here are some of the most intriguing and complex questions that physicists are trying to solve.

How are we going to reconcile quantum mechanics and relativity?

Two pinnacles of human ingenuity were both formulated at the beginning of the 20th century. These are quantum mechanics and Einstein’s theory of General Relativity. Over the last 100 years, they have been expanded upon and tested and they continue to serve scientists extremely well. But there’s one problem. They don’t work well together.

Relativity explains the large and massive, and its realm is gravity. Quantum mechanics describes the other three fundamental forces: electromagnetism, and the two nuclear forces, and everything it involves is small. The two theories are formulated and constructed in different ways so at present it’s not possible to use one to explain the other’s domain. Problems arise when they have to work together and usually we end up with nonsensical answers.

This tells us that there should be a better theory out there. One that can include both relativity and quantum mechanics. String theory and quantum gravity have been proposed to be such a theory, which is usually dubbed the theory of everything. So far we have not been able to test either of them to confirm these claims, due to limitations of technology. While the theoretical edifice of such a theory is being built, we also lack observations that push our trusty science to the limit. Nothing seems to properly violate either relativity or quantum mechanics. Finding such limits will help us make the theoretical efforts better directed to their goal. 

What are dark energy and dark matter?

Everything you see, the Sun, your phone, and the town of Lllanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch in North Wales are all made of regular matter. And regular matter is only 4 percent of the entire matter content of the universe. The rest is made by two unknown components – dark matter and dark energy

Dark matter was proposed almost five decades ago to explain how galaxies spin on their axis. If we take account of all the mass that we can see in stars and gas, their rotation doesn’t make sense. Dark energy was instead proposed 20 years ago to explain the accelerated expansion of the universe.

The effects of these two components are, in broad terms, well understood. We have used them in many simulations and they have produced predictions in agreement with what we observe in the universe. And yet after many years of study, we are none the wiser about their true nature.

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