There is an enormous list when we try to talk about unsolved problems in physics. From multiverse to supersymmetry, from an atom in a universe to the universe in an atom, many unsolved problems are yet to be solved. A number of scientists and physicists over decades of work have been able to solve many. But, as the curiosity of knowing the mechanism increases, the deeper we go into the working, the more problems we face. By solving them, we get a deeper insight into the nature of life itself.
From the microcosmos to the macro cosmos, through physics, we’ve been trying to unlock the mysteries of nature by one step at a time. From turning the sand to a satellite, we’ve made enormous efforts trying to decode the cosmic mechanism. Physics essentially means to understand the fundamental constitutes of the universe. The nature of how things work and why they work the way they do. From the patterns on flowers to the patterns of the milky way galaxy, from the grains of sand in the beach to the atoms in the universe, from stone writings to atomic writings; we are just curious about how this wonderful nature around us works the way it does. The first and foremost thing to know is, there are two main branches of physicists. Theoretical physicists and experimental physicists. Although both of them are curious about the same thing, the approach to the solutions is quite different. Theoretical physicists are the people who imagine, deduce and guess the new laws while on the other hand, experimental physicists are the people who conduct an experiment, imagine, deduce and then guess at the laws. Why these broad fields? One might ask; it’s just because, the principle of science essentially says, “ the test of all knowledge is an experiment”; but, we are stuck when we ask: if the experiment is the sole judge of scientific truth, what is the source of knowledge?
Physics is a broad field, extremely broad. But, it can be compressed into 3 major fields which can be seen as below.
Classical physics is the field that was first introduced in the society while there was still a cycle of natural philosophy. Through the introduction of classical physics, for the first time, we were able to understand that, everything which was happening in the universe was not completely random. From the projectile of a rock which is thrown to the movement of the galaxy, it was possible to be quantifiable, comprehend and understand through the path of physics and mathematics. Classical physics deals with topics like mechanics, thermodynamics, electricity, magnetism, optics, chaos theory.
Relativity, it based upon simple principle: perspective. It gives us laws that are the same everywhere in the universe. This is the core concept of relativity. From Galileo Galilee to Einstein, there was an enormous change in “relativity”. There was a complete scientific revolution when Einstein introduced his 2 groundbreaking theories. Theory of special relativity and theory of general relativity. General relativity simply means it’s a generalized theory of special relativity. ( but not simply: involvement of time). This discusses the complete space-time fabric of the cosmos from the big bang to black holes and beyond.
While we cover the topics of macro cosmos, in time we’ll look into the microcosmos. The quantum world. The whole of the scientific community was in complete shock when quantum physics first emerged in the 1920s. The study of wiggly jiggle particles which are always present; the study of atoms and subatomic particles and the way they behave. The action of particles in the quantum world, how they interact, how they react, how they form, how they die; their properties and many more which are extremely mind-boggling.
These are the broad field but there are many fields which are not yet discussed. ( cause the list is simply huge) and even the list of unsolved problems would go on (if written in-depth) . but, let us consider a few of the problems.
- The theory of everything
- Arrow of time
- Physical information
- Fine-Tuned universe
- Cosmic inflation
- Size of universe
- Baryon symmetry
- Dark matter
- Dark energy
- Shape of the universe
- Vacuum catastrophe
- Quantum gravity
- Extra dimensions
- Neutrino mass
- Supermassive black holes
- Ultra high energy cosmic rays
Theory of everything is a hypothetical theory that encompasses all of the fundamental framework of physics; from quantum mechanics to general relativity. It is one of the most intriguing concepts in the field of theoretical physics. This theory of everything would unify all the fundamental forces of nature, namely; gravitation, electromagnetism, strong interactions, weak interactions. The graph is given below:
The Arrow Of Time is one of the general unsolved problems in physics. It is described by the second law of thermodynamics. It is in correlations with entropy. Entropy simply means the amount of disorder. The universe seems to be having a high entropy stage where its distributing the order all across. The arrow of time simply points forward to the future and is the reason why we can’t do time travel. Without this arrow of time, the universe simply can’t exists.
Fine Tuned universe suggests that the occurrence of life on earth is very sensitive / very rare when we take the big picture of fundamental physical constants that rules the universe. These fundamental constants are generally dimensionless. For example, the fine structure constant alpha α which has the value 137.03597. If these fundamental values have a slightly different value, the universe would have evolved into something different.
Size of the universe is somewhat difficult to define. According to the general theory of relativity, far regions of space may never interact with ours even in the lifetime of the Universe due to the finite speed of light and the on-going expansion of space. For example, radio messages sent from Earth may never reach some regions of space, even if the Universe were to exist forever: space may expand faster than light can traverse it. Distant regions of space are assumed to exist and to be part of reality as much as we are, even though we can never interact with them. The spatial region that we can affect and be affected by is the observable universe. The observable universe depends on the location of the observer. By traveling, an observer can come into contact with a greater region of space-time than an observer who remains still. Nevertheless, even the most rapid traveler will not be able to interact with all of the space. Typically, the observable universe is taken to mean the portion of the Universe that is observable from our vantage point in the Milky Way. Since we don’t yet know about the size of the universe, as it is always expanding, the size of the observable universe is estimated to be Estimates for the total size of the universe, if finite, reach as high as 10^(10^(10^122)) megaparsecs.
Quantum gravity, broadly construed, is a physical theory (still ‘under construction’) incorporating both the principles of general relativity and quantum theory. Such a theory is expected to be able to provide a satisfactory description of the microstructure of space-time at the so-called Planck scale, at which all fundamental constants of the ingredient theories, c (the velocity of light in vacuo), ℏ (the reduced Planck’s constant), and G (Newton’s constant), come together to form units of mass, length, and time. This scale is so remote from current experimental capabilities that the empirical testing of quantum gravity proposals along standard lines is rendered near-impossible.
Extra dimensions: Einstein’s general theory of relativity tells us that space can expand, contract, and bend. If one direction were to contract down to an extremely tiny size, much smaller than an atom, it would be hidden from our view. If we could see on small enough scales, that hidden dimension might become visible. Imagine a balancing act in which a daredevil walks the cable of a suspension bridge, only able to move backward and forward, not left and right, nor up and down. The daredevil experiences only one dimension, but things that live on a smaller scale, such as ants, can move about in an extra dimension — circularly around the cable, in this analogy. String theory requires the existence of extra dimensions. Perhaps we will be fortunate enough to detect them directly in upcoming experiments, or infer their existence from early-universe cosmology. If so, we will have yet another confirmation of how the universe extends well beyond our everyday experience.
Super symmetry: The Standard Model has worked beautifully to predict what experiments have shown so far about the basic building blocks of matter, but physicists recognize that it is incomplete. Super symmetry is an extension of the Standard Model that aims to fill some of the gaps. It predicts a partner particle for each particle in the Standard Model. These new particles would solve a major problem with the Standard Model – fixing the mass of the Higgs boson. If the theory is correct, super symmetric particles should appear in collisions at the LHC.
At first sight, the Standard Model seems to predict that all particles should be massless, an idea at odds with what we observe around us. Theorists have come up with a mechanism to give particles masses that requires the existence of a new particle, the Higgs boson. However, it is a puzzle why the Higgs boson should be light, as interactions between it and Standard-Model particles would tend to make it very heavy. The extra particles predicted by supersymmetry would cancel out the contributions to the Higgs mass from their Standard-Model partners, making a light Higgs boson possible. The new particles would interact through the same forces as Standard-Model particles, but they would have different masses. If supersymmetric particles were included in the Standard Model, the interactions of its three forces – electromagnetism and the strong and weak nuclear forces – could have the exact same strength at very high energies, as in the early universe. A theory that unites the forces mathematically is called a grand unified theory, a dream of physicists including Einstein. in many theories scientists predict the lightest supersymmetric particle to be stable and electrically neutral and to interact weakly with the particles of the Standard Model. These are exactly the characteristics required for dark matter, thought to make up most of the matter in the universe and to hold galaxies together. The Standard Model alone does not provide an explanation for dark matter. Supersymmetry is a framework that builds upon the Standard Model’s strong foundation to create a more comprehensive picture of our world. Perhaps the reason we still have some of these questions about the inner workings of the universe is because we have so far only seen half of the picture.
Super massive black hole: These black holes typically have the range from 100,000 to billion or more solar mass. One of the most exotic regions in the fields of cosmology and astrophysics is to know how the supermassive black holes are formed. There are various theories, one which includes mid-range blackholes; but the complete story on how the supermassive black holes formed is still a question that needs to be answered. One of the possible theories are; during the formation of the early universe, when the gases were still in clutter, there is a possibility where the huge clouds of gas came together by the force of gravity and with the incredible force of gravity and enormous mass, it directly turned into a supermassive black hole. Another possibility is where the mid-range blackholes or the intermediate blackholes which have 10^5 to 10^9 solar masses collided during the early universe formation. There are also other kinds of blackholes: the ultra-massive blackhole. This has the mass 10^20 times of our sun. (Example TON 618).
These are just basic introduction of few topics which come under unsolved problems in physics. To understand what’s “unsolved” we need to get deeper into each of those regions. (Another blog will be dedicated to exploring the physics and math behind one of the unsolved problems in depth.)
The topics of unsolved problems don’t just come under a single field but comes under various sub fields:
- General physics/ Quantum physics
- Cosmology and general relativity
- Quantum gravity
- High-energy physics/ particle physics
- Astronomy and astrophysics
- Nuclear physics
- Atomic , molecular and optical physics
- Classical mechanics
- Condensed matter physics
- Plasma physics
Let’s consider astronomy and astrophysics; this is a vast field. But what does that field contain? Here’s the list:
- Planetary astronomy
- Planetary systems
- Are there planets beyond Neptune?
- Rotation rate of Saturn
- Stellar astronomy and astrophysics
- Solar cycle
- Coronal heating problem
- Origin of stellar mass spectrum
- Fast radio bursts
- OH-My-God particle
- Tabby’s star
- Galactic astronomy and astrophysics
- Galaxy rotation problem
- Age-metallicity relation in galactic disk
- Ultra luminous X-ray sources
- Black holes
- Gravitational singularities
- No-hair theorem
- Black hole information paradox and black hole radiation
- Final parsec problem
- Dark matter
- Dark energy
- Baryon asymmetry
- Cosmological constant problem
- Size and shape of the universe
- Cosmic inflation
- Horizon problem
- Axis of evil
- Origin and future of the universe
- Extra-terrestrial life
- Is there other life in the universe?
- Nature of Wow! signal
As you can see, this is a huge topic with a length of various subtopics. With one’s curiosity, they can explore each or any one of the fields to get a deeper insight.
Many scientists around the world are working their life to unlock the mystery of cosmos, equation by equation. Not all problems are left unsolved. Some might take a decade, some might take a century or more. But with, enough evidence and knowledge, what was ones unsolved, will be solved. Few of such solved problems are:
- Origin of short gamma-ray burst (1993 -2017)
- Time crystals (2012-2016)
- Gravitational waves (1916-2016)
- Existence of Pentaquarks (1964-2015)
- Higgs boson and electroweak symmetry breaking (1963-2012)
- Faster than light neutrino anomaly (2011-2012)
- Numerical solution for binary black hole (1960s-2005)
- Long duration gamma ray bursts (1993-2003)
- Solar neutrino problem (1968-2001)
- Cosmic age problem (1920s-1990s)
- Nature of quasars(1950s-1980s)
Many scientists and even more space enthusiasts are required to be a part of the solution for few of these problems. Believe it or not, when solution(s) for one of the problem(s) is found, then the group of people who found the solution is literally changing a whole generation of population and opening a tremendous possibilities and opportunities for advanced technologies. Today’s science fiction may be tomorrow’s reality.