this video is brought to you by brilliant click the link in the description to sign up for free and support this channel there was a time when everything that happened was seen as random or a seeming Miracle sometimes attributed to the Unseen hand of a Divine being then Greek and other ancient civilizations began to explore rationality and logic to explain how the universe works a paradigm shift came through the likes of Galileo and Newton and the introduction of classical mechanics the universe was then viewed as a kind of cosmic clock ticking with mathematical Precision where
almost every movement and phenomenon could be explained and predicted through observations and equations in the early 20th century this view of a mechanical deterministic and predictable Universe was shattered with the Advent of Relativity and quantum mechanics time was no longer set in stone and the precise location of particles was no longer measurable Einstein Planck boar and Schrodinger LED this new paradigm shift this might seem like the end of the story but there has been one additional more recent Paradigm shifting development in physics that perhaps did not receive as much fanfare but it is undoubtedly equally
profound and that is how quantum mechanics was supplemented and made more complete by Quantum field Theory or qft it is the basis of the best theory we have in physics today to explain nearly everything called the standard model of particle physics what is quantum field Theory why is it necessary how is it different than quantum mechanics that's coming up right now [Music] classical mechanics has been and continues to be used to explain many phenomena that we can observe consider a planet orbiting a star we can use Newton's laws to model it fairly accurately if the
planet were to somehow lose its kinetic energy or slow down it would spiral into the star and collide now consider something conceptually similar an electron orbiting the proton of a hydrogen atom in this case we could again try to use Newton's laws to model it instead of the attractive force of gravity for the star and Planet the two objects electrical charges keep it bound together this is where classical mechanics fails because as we know from Maxwell's laws an accelerating charge creates electromagnetic radiation and the constantly changing direction of the electron creates an acceleration this means
the electron would constantly give up photons losing energy in the process it would thus spiral towards the nucleus and Collide but we know that no such thing actually happens in reality atoms are stable an electron does not crash into the nucleus why because we were using the wrong tool to describe the model of an atom classical mechanics we have to use a new tool quantum mechanics Niels Bohr proposed that the electron maintains a stable orbit because its energy is quantized it can only be in an orbit that is an integer multiple of a minimal quanta
and its lowest energy state is the lowest orbit that the electron can have it cannot be lower this minimal quanta by the way is proportional to the Planck's constant in Newtonian physics we think of objects as discrete particles having very specific and measurable properties such as a mass x momentum Y and position Z and quantum mechanics our objects are wave functions described by some completely different mathematics this is shown by the Schrodinger equation which is perhaps the most important equation in quantum mechanics here the location of a particle is unknown until the moment of measurement
we cannot know where it is beforehand we can only know the probability of finding it at any specific location prior to measurement the wave function depicts a kind of smearing out of its location thus in the quantum mechanical model of the hydrogen atom the electron is not spinning around the nucleus like a planet around a star it's in some unknown location at some unknown distance from the nucleus all we know is that the chance of finding the electron at any specific location or distance from the nucleus has a probability associated with it and we can't
determine the location in advance of measuring it so the better model of the atom is like a cloud around a fuzzy nucleus the White Cloud represents the probability cloud of the location of the electron note that the nucleus 2 would be fuzzy as well since it is also a Quantum object but its Cloud would be more localized than the electrons now you might think this is a great model we know everything now we can stop here but we can't because quantum mechanics has some problems too there are some things it cannot explain and we get
the wrong results just like when we tried to explain the electrons orbit with the classical formulation first of all quantum mechanics is not relativistic that is it will give you wrong results if the quantum object is moving close to the speed of light Schrodinger's equation simply doesn't obey Einstein's theory of special relativity the Practical result of this is that it doesn't incorporate a speed limit the speed of light needed to make causality work for example it allows for two measurements to influence each other faster than light this would mean that there would be some reference
frame in which the future could influence the past breaking causality a second problem with quantum mechanics is that it only tells you how a particle evolves over time that is how it goes about its business it does not tell you how it is created or annihilated so it can't account for things like beta Decay due to the weak nuclear force where neutrons transforms into a proton an electron and an antineutrino in this case quantum mechanics breaks down because it doesn't work if we change the number of particles in the case of the beta Decay I
just described the down Quark of a neutron decays into an upquark changing the neutron to a proton at the same time emits an electron and an antineutrino with a mediating W boson this change to other particles can't be described by quantum mechanics this is where Quantum field Theory explains things that quantum mechanics cannot explain on its own so what is quantum field Theory well it's a mathematical framework that combines classical field Theory a classical field would be like a magnetic field as described by James Clark Maxwell special relativity and quantum mechanics there is a field
for every particle of the standard model so in our beta Decay example there would be a field for the down Quark the W boson the up Quark the electron and the anti-neutrino all these fields extend out in all of space-time in other words the fields are always there and exist everywhere including inside your body now although they exist everywhere and you can't see them they are not nothing they are teeming with virtual particles these are particle anti-particle pairs that get created and destroyed so for example the down Quark field will always have some spontaneous creation
down quarks and anti-down quarks which get created annihilated almost instantly they come in and out of existence constantly these virtual particles can't be measured but nature allows the creation of these virtual particles by letting them borrow energy from the vacuum as long as that energy is put right back into the vacuum this happens so quickly that it's as if nature doesn't register them as real measurable particles we can visualize these fields as a kind of ocean just like the ocean wave has some turbulence the fields always have a kind of turbulence even in their ground
state of minimal energy this turbulence is due to the virtual particle creation and Annihilation I just described in these turbulent Seas if there's enough energy a large wave can be created we can be measured these are the real particles so in the up Quark field for example an up Quark will be created if there's energy of 2.3 Mega electron volts or Mev which is the mass of one up core two quarks will be created if there's energy of 4.6 MAV so a particle is nothing more than an excitation in this field these excitations are quantized
not continuous so the fuels can only create particles in integer increments they cannot for example have one and a half up quarks only two quarks or three quarks Etc now energy can be transferred between two Fields via a mediating boson field this is considered an interaction or a force matter particles can't interact on their own without a mediating Boson so while in quantum mechanics there's no way for the neutron to split its energy into three different particles a proton electron and an anti-neutrino in Quantum field Theory this can be done via energy exchange between the
fields you start with the fields of all the different particles which are always there and you finish with the fields of the same particles some of them just have more or less energy after the exchanges of energies depending on the interaction so in our beta Decay for example you start with the down Quark field this field transfers its energy to the up Quark field and the W boson field the W boson field then transfers its energy almost immediately to the electron field and the anti-neutrino field so we started with one particle in the down Quark
field and we ended up with three particles simply by the fields exchanging energy note that although the number of particles changed the total energy is always conserved if you add up all the masses and kinetic energy at the beginning they will add up to all the masses and kinetic energy at the end in other words the energy of the fields is the same before and after the energy has changed so by having Quantum fields we can mathematically account for and model creation annihilation of particles as well as the mechanism of Force exchange the icing on
the cake is that the theory is fully relativistic meaning it's free of causality violations but even this modification of quantum mechanics is not perfect for example it's still missing gravity we do not have a Quantum field theory for Gravity if we did it would mean that we could model a field for the theoretical graviton particles and gravity would be mediated between matter particles by the exchange of this graviton boson so even qft which is extremely accurate for the forces and particles we do know about in the standard model remains as yet incomplete the fact that
we don't have this tells us something it reminds me of the saying that when you have a hammer as your tool everything looks like a nail our tool is qft so far everything we know has been a nail so either gravity is not a nail or maybe we just don't really know how to use the hammer but still in my view qft is probably the most beautiful theory in science and here's why because it tells us that the Universe and everything in it including us and all living things the whole planet every Star every Galaxy
and even things outside the visible Universe are all connected everything even our thoughts dreams and ideas are composed of excitations in the same Quantum fields and all these fields extend to not only all of space but all of time the universe is made of the same basic stuff and we are all simply a series of excitations in it so when someone says we're all one or that we're all connected to the universe this is not just a fanciful idea but has a real physical meaning I find this to be beautiful and another beautiful thing is
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