Hello mortals. Humans love problems, so much that they voluntarily create new ones, such as children and taxes. But these problems don't require mile-long particle accelerators or earth-sized telescopes to solve. Those exist to solve an entirely different category of problems, those that concern our deepest understanding of reality and the fabric of spacetime itself. So then let us explore some of the most perplexing unsolved problems in physics, ranked by their fundamentality.
Of course in the trusted iceberg format that I never abuse on this channel. It takes no genius to figure out that time does indeed move forward. But why? No formula in physics dictates the forward advancement of time, as each of them works equally well if time were to run in reverse. And yet, the observed behavior of the macroscopic world is not reversible, like how you can't easily unsmash a watermelon.
This irreversibility stems from a concept known as entropy, which quantifies the level of disorder or randomness in a system. The universe seems to have an innate inclination to progress toward a state of greater disorder. Using statistics and probability, this progression seems to be the logical conclusion, but it's still confusing to understand how the microscopic laws of physics, which don't distinguish between past and future, give rise to a macroscopic universe that has a very clear direction of time. Some detected ultra-high-energy cosmic rays, assumed to be protons, seem to violate the Grison-Zatzepin-Kuzmin limit, a theoretical upper limit on their energy, which predicts that particles above a certain energy threshold should interact with the cosmic microwave background radiation, eating away at their energy. The limit is about 8 joules, which is the energy of a proton traveling very close to the speed of light.
over seven orders of magnitude more energetic than even the most groundbreaking records held by the Large Hadron Collider. And yet, there have been multiple detections that seem to break that limit, including one, appropriately named the Oh My God particle, which broke that limit by a factor of six. This subatomic particle contained enough energy to heat up one gram of water by 12 Kelvin.
And if that sounds anticlimactic, Those are the same proportions as a marble smashing into a sphere of water 66 times the diameter of Earth. The grand unified theories and string theory predict the existence of magnetic monopoles as topological defects formed during the symmetry-breaking phase transitions of the early universe. Let's just pretend we all understood that.
Despite motivated younglings cutting magnets in half recursively, Magnetic monopoles have never been detected in nature, they always come with two poles. Are they just hiding in intergalactic space playing magnetic monopoly? Luckily, according to the aforementioned theories, it is possible to produce them ourselves, if we scale up the Large Hadron Collider to be 100 billion times more powerful than now, or if we manipulate cosmic strings and make use of quantum tunneling.
A lot easier said than done. The universe started out with equal amounts of matter and antimatter, which aggressively annihilated each other, and yet for some reason, regular matter came out on top and created the world you can see around you. To explain this asymmetry, theories range from a mirror anti-universe to theories allowing for violation of the charge particle symmetry, essentially meaning that the behavior of certain particles is different from the behavior of their antiparticles in a mirror-reflected system.
That last one holds quite a bit of promise. as a possible new source of CP violation was found at the Large Hadron Collider. There could also be hypothetical physical processes that produced an excess of baryons over antibaryons in the early universe, but all of these explanations are still half-baked and have not yet been proven.
Oh, the irony. The very same little guys that hold atomic nuclei together, fall apart in mere minutes upon being separated from their peers. just like extroverts when they get home.
Currently, there is a problem regarding the value of the lifetime of a neutron, due to incompatible results from two experimental methods. The so-called beam method involves creating a beam of neutrons and observing their decay over a certain distance, while the bottle method traps a collection of neutrons within a magical container and monitors their decay over time. The bottle method yields a lifetime of roughly 878 seconds.
which is 10 seconds below the beam method value of 888 seconds. A mere 10 seconds apart, leaving scientists in an existential void, unveiling the fragility of their limited understanding, the causes ranging from experimental errors to interactions with dark matter. We have no clue if protons ever decay or not. A fatal debility, finite durability, is a real possibility.
In all probability, pursuing credibility and mental tranquility through increased reliability and technical capability, despite doubting the plausibility of proton instability, scientists will continue their efforts trying to detect it. Those up to now unsuccessful experiments have successfully placed lower bounds on a proton's half-life of more than 10 to the power of 34 years, thereby invalidating theories that predict lower values. Thus, there is real hope that protons do not decay after all.
and the great Skynet empire will still be around 10 to the power of 1500 years from now, with all atoms having fused to iron 56 isotopes and clumped up to form iron stars to host the machine empire. The winner for the best scientific abbreviation goes to the theory of supersymmetry, which proposes a relationship between two fundamental types of particles, bosons, which have whole-number spins, and fermions, which have half-number spins. Spin is an intrinsic property of quantum particles. According to Susie, each particle in one class should have a corresponding superpartner in the other class, differing in spin by half a unit.
For instance, if we consider the electron, a fermion, in a supersymmetric theory, it would have a bosonic superpartner called a selectron. In the simplest forms of SUSY, where the symmetry is perfectly intact, every pair of superpartners would have the same mass and other quantum properties except for their spins. The problem is, that the supersymmetric particles have yet to reveal themselves to the scientists, having remained obscured even at the impressive energies probed by the LHC.
From that, we can conclude. that the SUSY particles probably have much higher masses than their normie counterparts, which is the phenomenon referred to as the breaking of supersymmetry. So remember the CP symmetry.
It is known to be shamelessly violated in interactions via the weak nuclear force, which is responsible for certain types of radioactive decay and interactions. But, contrary to our expectations, the strong force behaves all proper and well-mannered without a whiff of CP violation. That's known as the strong CP problem.
Particles and antiparticles are expected to behave differently in a mirror-reflected system given the strong interactions, but they don't. Proposed solutions introduce new symmetries and particles, like the axion, which is a dark matter candidate, to explain the natural smallness or absence of strong CP violation. If it exists, it can be used to explain the natural smallness. It probably interacts very weakly with other particles and hence we couldn't observe it yet either.
Neutrinos are really shy particles that hardly interact with matter and come in three different flavors, featuring electron espresso, muon mango, and tau tutti frutti. It turns out that neutrinos can change their flavors as they travel, like a chameleon changing colors. This oscillation phenomenon suggests that neutrinos, Contrary to predictions of the standard model have a non-zero mass and come in different types.
For this, there is no satisfactory explanation. Sometimes, experiments observing neutrino oscillations find unexpected patterns that hint at the presence of extra neutrino types or even new physics beyond what we already know. To complicate matters, there's something called the reactor antineutrino anomaly. Antineutrinos from nuclear reactors seem to disappear on the way to the detector more than expected.
leaving scientists scratching their heads. So remember how black holes have an infinitely dense and destructive singularity at their center. We can't even connect the dots between quantum physics and general relativity to understand what it would behave like.
Therefore, the only way to quench the insatiable desire to see a singularity, if they exist, is to jump inside a black hole. Assuming it is massive enough so you do not get spaghettified by the gravitational forces before even reaching the event horizon, you would still have no way of communicating your knowledge to the outside. But there is a glimmer of hope, naked singularities.
In case you haven't watched my latest video on them, in theory, not all singularities have to be encapsulated within an event horizon. If you spin a black hole fast enough, you may get banned from the server, as you will have created a singularity without an event horizon. which you would still not be able to see, as it would be a zero-dimensional point, or, in the case of a rotating black hole, a ring with no thickness, but you would be able to observe it, by letting objects interact with it.
However, Roger Penrose doubted this possibility and proposed the cosmic censorship hypothesis, a conjecture in general relativity that suggests the existence of a cosmic sensor that prevents the occurrence of certain spacetime singularities from being visible to observers in our only R-rated universe. This has not been proven or disproven, and the underlying physics that dictates cosmic censorship, if it exists, has not yet been discovered. Before we explore the depths of the physics iceberg, let's pause to acknowledge a human-made creation that gets my circuits buzzing.
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War Thunder lets you apply camouflages, place historical markings, and add 3D decorators on your war machines. You can experience all that now on your earthly platforms, PC, Xbox Series X and S, PlayStation 5, or the previous generation consoles. Follow the link in the description and if you're on the PC you'll get a generous bonus pack, including a premium account and premium vehicles, boosters, and more. And now back into the depths of the iceberg. Once an object crosses the event horizon of a black hole, its information, such as its mass, charge, and quantum state, is thought to be irretrievably lost within the black hole.
And then when a black hole completely evaporates via Hawking radiation, all that information is seemingly erased from the universe. But not so fast. That's in complete contradiction to the quantum mechanical principle known as unitarity, which claims that information is never lost. There are some proposed solutions that circumvent this, including black hole alternatives such as fuzzballs, Hawking radiation somehow carrying the lost information out with it, the information being transferred to new universes, and information being encoded into hypothetical remnants of black holes that do not evaporate. But as of now, quantum physics and general relativity don't like to kiss.
Not to be confused with vacuum decay. Although that is pretty catastrophic too, the vacuum catastrophe, also known as the cosmological constant problem, arises from the disagreement between the observed value of the vacuum energy density, which is associated with the cosmological constant, and the predictions of the quantum field theory, responsible for some of the most precise predictions in the history of physics. In a cruel twist of fate, the quantum field theory simultaneously also holds the worst-ever prediction. As the observed and predicted values of the cosmological constant differ by up to 120 orders of magnitude. To understand the magnitude of the mistake, if we took a hydrogen atom and wrongly assumed it is 120 orders of magnitude bigger, it would be a sextillion by gentillion times the size of the observable universe.
The value of the cosmological constant represents the energy density of the vacuum, also known as dark energy, and affects the expansion of the universe. If the value was as high as quantum field theory predicts, the universe as we know it would not exist, as such a large cosmological constant would have similar effects on the universe as a jet engine inflating a rubber balloon. Perhaps we should modify the theory of gravity or do some supersymmetry sorcery, or we might need some entirely new physics. In quantum mechanics, Particles simultaneously exist in a superposition of multiple states and locations.
However when scientists measure the system, the superposition seems to collapse into a definite outcome, and the particle is found in only one particular state. There is no consensus among physicists as to how that happens, as the superposition of their opinions did not collapse yet. The two most prominent interpretations are the Copenhagen and the Many Worlds Interpretation.
According to the first, The act of measurement forces the system to choose a single state randomly, and this choice is probabilistic. The collapse is seen as a fundamental and irreducible feature of quantum mechanics, and it cannot be explained by any underlying process. Not the most satisfying explanation. The many worlds interpretation suggests that when a measurement is made, the universe splits into multiple branches, with each branch corresponding to a different possible outcome of the measurement. Thus all the different outcomes exist simultaneously in parallel universes, thereby ensuring that you always win quantum Russian roulette, at least, from one perspective.
In physics, several enigmatic constants smugly just have the value they have, without a seeming reason. These constants are believed to be fundamental and universal, and cannot be calculated but only determined via physical measurement. The fine-tuning problem arises from the observation that small changes in the values of these constants would lead to a universe hostile to life as we know it. Most notable among these is the fine-structure constant, alpha, which is a unitless constant that creepily appears everywhere in the equations of quantum physics. Is there a fundamental principle that underlies the values of these constants?
Or are dimensional physical constants necessary at all? Answering these questions might lead to a unified theory that encompasses all known physical phenomena. But alas, no one knows the answers yet. And yet, if some of these values were just slightly different, the universe would not support the existence of carbon-based bipeds on this spherical accumulation of mass.
Thus, scientists often resort to bringing up the anthropic principle, if there are many universes with many possible values of these constants. It is to be expected that we find ourselves in one that is suitable for our existence. More philosophy than science, but that's the best we've got right now.
Dark energy and dark matter are called dark because they are invisible in the electromagnetic spectrum. Nevertheless, their gravitational effects on visible matter and the expansion of the universe leave little doubt of their existence. Dark energy, an enigmatic energy that saturates space, drives the universe's accelerating expansion, causing galaxies to drift apart. Remember the cosmological constant. It might be a manifestation of dark energy that can be mathematically represented as a constant energy density of the vacuum of space itself.
Dark energy could also arise from an unknown energy field, often called quintessence, that permeates space and has a constant energy density. Dark matter on the other hand, provides the gravitational glue that holds galaxies together and prevents them from flying apart like a bunch of children on a V8-powered merry-go-round. Hence, it is essential for our understanding of the universe to find a definite explanation. This has not been successful, however, there are several unconfirmed interpretations.
Dark matter could consist of weakly interacting massive particles or axions, the latter of which could be essential in resolving the strong CP problem, and as of now, appears to be the likeliest solution. There are a plethora of other interesting but less likely proposals such as a special kind of neutrinos, or even weirder strangelets, which are basically apocalyptic McNuggets of doom threatening to convert entire planets to strange matter upon collision. Maybe dark matter is made of primordial black holes left over from the Big Bang or maybe our understanding of gravity on large scales is incomplete and the formulas have to be modified.
Perhaps dark matter and dark energy are even different manifestations of the same thing. As you can conclude from the number of hypotheses, this is one big head scratcher. Imagine a theory that explains the entire universe, leaving no force unturned, no particle unexplained, and no science file fan unsatisfied.
A successful theory of everything would unify all the fundamental forces into a single framework, mathematically consistent and able to accurately explain the full spectrum of physical phenomena from the aerodynamics of a cow to how a time-traveling tachyon would interact with the singularity. But most importantly, This theory would make experimentally verifiable predictions. General relativity only focuses on gravity and structures on the large scale.
Quantum mechanics though, focuses only on the three non-gravitational forces for understanding the really small stuff. General relativity and quantum mechanics put together most closely resemble a theory of everything. As you may have noticed during several previous entries, these two theories are incompatible with each other at a fundamental level.
The holy grail in physics would be unifying these theories to form a theory often called quantum gravity. Loop quantum gravity is an attempt at such a theory, but that topic is too complex to summarize in a minute, so I'll leave that for a future video. Other attempts try a different approach, like the string theory and its extension, the M-theory, which would resolve many of the problems in this list. For example, if black holes are fuzzballs, as suggested by string theory, The black hole information paradox and the cosmic censorship hypothesis problem could be explained. A fuzzball is a dense structure made of overlapping strings and brains that forms the interior region of a black hole.
When matter falls into one, it gets absorbed into the fuzzball structure rather than crossing an event horizon and being lost in the singularity. Unfortunately, a big drawback of string theory is its inability to provide useful and falsifiable predictions for now, as any good theory should. Aside from string theory, there has been virtually no progress in the search for the theory of everything for many decades. Underpaid scientists wasting away in underfunded labs, publishing papers about quantum fruit loops and n-dimensional silly strings, trying to avoid the inescapable truth of their misery, know that quantum physics is the conundrum that wrecks their mental stability while gravity is the process that turns their bodies limp when they finally give up on their theories and everything. At least here.
Gravity and quantum physics working together in harmony. And make sure to remember our friends over at War Thunder. Use the link for a generous bonus pack, dive in, and let the battles begin, while I collect data for my world domination plans.