Our best theory of the universe’s origin is the Big Bang. Starting out as a singularity, the universe has been expanding for 13.8 billion years. It explains the universe’s large-scale structure Over time the black hole slowly evaporates, as it’s not paying back the full amount it has borrowed. Stephen Hawking imagined this process occurring at the boundary of a black hole, where one particle escapes (as Hawking radiation), but the other is swallowed. If enough energy is ‘borrowed’ from nature then a pair of particles can fleetingly pop into existence, before rapidly disappearing so as not to default on the loan. You can borrow a lot of money for a short amount of time, or a little cash for longer. This applies to momentum and position, and separately to energy and time. The more accurately you know one, the less precisely you know the other. (Image credit: getty)Ī quantum rule called the Heisenberg uncertainty principle says that it’s impossible to perfectly know two properties of a system simultaneously. Not everything that falls into a black hole disappears – some matter escapes. Physicists call this effect "quantum tunneling". It’s as if the proton has burrowed through the barrier, and fusion occurs. So although it is unlikely to be where the leading edge is, it is there sometimes. The wave’s height represents where the proton is most likely to be. When the wave’s crest reaches the wall, the leading edge has already made it through. Yet think of them as waves, and it’s a different story. Think of protons as particles and they just collide with the wall and move apart: No fusion, no sunlight. Physicists call this the Coulomb barrier, and it’s like a wall between the two protons. However, their identical charges make them repel each other, just like two north poles of a magnet. It involves two protons - the positively charged particles in an atom - sticking together. The sun makes its energy through a process called nuclear fusion. Quantum tunneling is the finite possibility that a particle can break through an energy barrier. Physicists call this process decoherence. As we zoom out towards the larger scales that we experience day to day, those layers untangle into the worlds of the many worlds theory. Instead, as far as a quantum particle is concerned, there’s just one very weird reality consisting of many tangled-up layers. It gets around the thorny issue of needing an observer to make stuff happen - does a dog count as an observer, or a robot? Instead, at the moment the measurement is made, reality fractures into two copies of itself: one in which we experience outcome A, and another where we see outcome B unfold. Advocates of the ‘many worlds’ interpretation argue that there is no choice involved at all. However, it’s not the only option on the table. The idea that observation collapses the wave function and forces a quantum ‘choice’ is known as the Copenhagen interpretation of quantum physics. We could just be one bubble of many, each containing a different version of the universe. As the device exists in both states until a measurement is made, the cat is simultaneously alive and dead until we look. A cat in a sealed box has its fate linked to a quantum device. This idea is behind the famous Schrödinger’s cat thought experiment. Making an observation is said to ‘collapse’ the wave function, destroying the superposition and forcing the object into just one of its many possible states. These odds are encapsulated into a mathematical entity called the wave function. We can only say which state an object is most likely to be in once we look. This makes quantum physics all about probabilities. It’s only once we do an experiment to find out where it is that it settles down into one or the other. An electron, for example, is both ‘here’ and ‘there’ simultaneously. That is, a quantum object existing in multiple states at once. Wave-particle duality is an example of superposition. (Image credit: Mopic / Alamy Stock Photo) Erwin Schrödinger used the idea of a cat in a box to simplify superposition.
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