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David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.
Next time you're leaning your elbow on the table, what would you think if your arm fell right THROUGH the table? Well, you'd probably think that you'd gone crazy, but if you were a professor of quantum theory, you might be able to explain what happened because quantum theory tells us that it's actually POSSIBLE! Quantum theory is a body of work in physics that explains the way the universe works on the tiniest scales. The regular laws of physics, from Newton's laws to thermal physics, just don't help us when things are super small. They no longer work.
Quantum theory is... well, it's WEIRD. But it helps us explain a lot of things. Light behaves like a particle and a wave, depending on the exact scenario, and quantum theory helps us explain this. The behavior of elements in the periodic table can also be explained by quantum theory. And just observing a particle has an effect on that particle; the particle would be in a different state if you'd never bothered to look.
Even the weirdest conclusions you can make from quantum theory have led to real, practical applications. Quantum theory has been responsible for many inventions that we take for granted today, from flat-screen televisions to sensors in digital cameras to lasers in DVD and Blu-ray players.
One of the basic ideas of quantum theory is that you can never know with absolute certainty the position of a particle. Instead of a particle having a position, it has a wavefunction. A wavefunction is an equation that tells you the probability of a quantity (like position) having various values. So, you'll know which is the most likely position the particle holds, not its actual position.
Once you measure the position of the particle, the wavefunction is said to 'collapse' into an actual, specific position. This is why, as mentioned previously, measuring a value actually affects the thing you're measuring. If this strikes you as odd, you're not alone. But this is the source of wave-particle duality; when you measure the particle's position, it goes from behaving like a wave (with a wavefunction) to behaving like a particle (with a specific position).
Another key idea in quantum theory is the Heisenberg Uncertainty Principle. This principle relates various pairs of quantities and says that the more precisely you know one value, the less precisely you know the other. For example, if you know really accurately the position of a particle, you'll hardly have any idea what its velocity is, and vice versa.
Schrodinger's Cat is such a famous thought experiment in quantum theory that it deserves its own section. The Schrodinger's Cat scenario shows what happens if you try to apply quantum physics to regular, everyday objects like a cat. So, the thought experiment goes, if you put a cat in a closed box containing a breakable vial of poison, the cat could be dead OR alive, depending on whether it knocked over and smashed the vial. The only way to know is to open the box.
But, if we apply quantum theory to this situation, the cat is described by a wavefunction showing the probability of both the cat being dead or alive. This means that the cat must be dead AND alive simultaneously. So, quantum physics really doesn't make much sense on our everyday scales. Schrodinger used this to make the point that we need to find some way to bridge the expanse between quantum physics on tiny scales and regular physics on everyday scales.
So, last of all, let's go back to the scenario that opened this video: putting your elbow through the table. Quantum theory says that this is possible - after all, a table is mostly empty space, like all objects. Unfortunately, there is a rather enormous catch. Yes, there is a small, but real possibility of your elbow going through the table. But that probability is SO small, that you would have to wait... let's say, several times the age of the universe for it to happen. Sorry to disappoint you.
Quantum physics is a body of work in physics that explains the way the universe works on the tiniest scales. The laws of physics that we use for our everyday scales don't work on this level. Uncertainty is a big part of quantum theory. Instead of a particle having a position, it has a wavefunction. A wavefunction is an equation that tells you the probability of a quantity (like position) having various values. When you measure the particle's position, the wavefunction 'collapses' into a specific position.
Another quantum physics idea is called the Heisenberg Uncertainty Principle, and says that the more precisely you know one value, the less precisely you know the other. You can't, for example, know the position and velocity of a particle with complete precision.
Schrodinger's Cat is a thought experiment that demonstrates how quantum physics can't work on everyday scales. A cat put in a box with a vial of poison, according to quantum theory, is simultaneously both dead and alive. This is quite obviously nonsensical, so we need a unifying theory that brings quantum theory and larger scale physics theories together.
Quantum theory explains how light can be both a wave and a particle, why elements react the way they do, and how particles are affected by being observed. It's led us to develop flat-screen televisions, sensors in digital cameras, and lasers in DVDs and Blu-ray players, among many others.
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Back To CourseFundamental Physics
22 chapters | 253 lessons