In early 1900’s, the British physicist Lord Kelvin claimed: "There is nothing new to be discovered in physics now. All that remains is more and more precise measurement." But in less than three decades, quantum mechanics and Einstein's theory of relativity had revolutionized physics. Currently, no physicist would ever think of claiming that our knowledge of physical universe is near completion. Because each new finding appears to unravel a Pandora's box of even greater, even deeper physics questions. So here are my choices for the most deep and open questions of all. What is dark energy: No matter how scientists manipulate the numbers, the universe basically doesn't add up. Even though gravity is pulling inward on space, it just keeps growing outward faster and faster. To provide a solid explanation for this, astrophysicists have suggested an unseen agent that overpowers gravity by pushing space-time apart. Astrophysicists call it dark energy. In the most broadly recognized model of dark energy, it is a "cosmological constant": a characteristic property of space itself, which has "negative pressure" pushing the fabric of space-time apart. As space expands, more space is produced, and as the more space is produced, more dark energy is created. Centered on the observed rate of expansion, astrophysicists know that the totality of all the dark energy must make up more than 70 percent of the entire contents of the cosmos. But so far no one knows how to look for it.
So far, physicists can't really crack the set of equations that defines the behavior of fluids, from water to air to all other liquids and gases. Actually, it isn't even acknowledged whether a general solution of the so-called Navier-Stokes equations even exists, or, if there is a solution, whether it explains behavior of fluids everywhere, or comprises characteristically incomprehensible points called singularities. As a result, the nature of chaos is not well understood. Physicists and mathematicians still wonder, is the climate purely difficult to predict, or fundamentally unpredictable? Does turbulence exceed mathematical explanation, or does it all make sense when you use the right math?
Is string theory correct?
When physicists assume all the basic particles are essentially one-dimensional loops, or "strings," each of which beats at a dissimilar frequency, physics gets much cooler and easier to understand. String theory permits physicists to reunite the laws governing tiny particles, called quantum mechanics, with the laws governing massive things in space, called general relativity, and to unite the four fundamental forces of nature into a particular framework. But the problem is, string theory is only useful in a universe with 10 or 11 dimensions: three large spatial ones, six or seven compressed spatial ones, and a time dimension. The compressed spatial dimensions — along with the vibrating strings themselves — are almost a billionth of a trillionth of the size of an atomic nucleus. There's no imaginable way to discover anything that small, and so there's no acknowledged method to experimentally confirm or invalidate string theory.
Why is there more matter than antimatter?
The question of why there happens to me more matter than its oppositely-spinning and oppositely-charged, antimatter, is essentially a question of why anything happen to exists at all. One assumes the universe would treat matter and antimatter equally, and that is why, right after the Big Bang, equal amounts of matter and antimatter would have been produced. But if that had happened, there would have been a total extermination of both: Protons would have negated with antiprotons, similarly electrons with anti-electrons (positrons) and neutrons with antineutrons, and so on, leaving a cloudy sea of photons in a matterless vastness. For some unknown reason, there was extra matter that didn't get crushed, and here we are. For this, there is no recognized explanation so far.
Are there any parallel universes?
Astrophysical data recommends that space-time could be "flat," rather than curved, and thus that it goes on endlessly. If so, then the area we can see (which we call as "the universe") is just one bit in an enormously large "quilted multiverse." At the same time, the regulations of quantum mechanics claim that there are only a limited number of thinkable particle formations within each cosmic patch (10^10^122 separate possibilities). So, with an infinite number of cosmic patches, the particle arrangements inside them are forced to repeat — infinitely several times over. This means there are infinitely numerous parallel universes: cosmic regions precisely the same as ours (comprising someone exactly like you), as well as patches that vary by just one particle's position, patches that vary by only two particles' positions, and so on down to patches that are entirely different from ours. Again there is still no solid evidence for the presence of parallel universes.