Quantum Field Theory visualized
Summary
TLDR本動画では量子場論の基礎について解説しています。量子力学では粒子の位置は確定しないため、波動関数で表現される確率分布とされています。しかし、量子力学は粒子数の変化や粒子間での相互作用を考慮に入れません。そこで、特殊相対性理論と量子力学を統合した新しい数学的枠組みである量子場論が提案されました。この理論では、空間時間を量子場で満たし、その場に粒子が存在し、相互作用を通じて力が生じることを説明しています。標準模型はこの理論に基づいて、粒子の家族とその相互作用を記述していますが、重力を説明する一般相対性理論との統合はまだ課題です。
Takeaways
- 🌌 量子场论は量子力学と特殊相対性理論を統合した理論で、粒子の振る舞いをより詳細に説明します。
- 🎲 量子力学では、粒子は確定的な位置を持っておらず、その存在は空間全体に確率的に分布されています。
- 🔄 量子力学は時間の経過とともに粒子の進化を記述できますが、粒子数の変化や粒子間の相互作用を考慮に入れません。
- 🌀 量子場論では、空間時間に広がる「場」を用いて、粒子をその場の局所的な表現と考えます。
- 🔢 特殊相対性理論に従い、場は空間時間の対称性(翻訳、回転、参照フレームの変化)を尊重しなければなりません。
- 🌀 場にはスピン(0, 1, 1/2など)の異なる数学的オブジェクトが含まれており、これらは相対性理論の対称性に従っています。
- 🌐 量子場は、古典的な場から量子場への遷移を通じてエネルギーレベルを持ち、粒子はその場のエネルギーの摂動として現れます。
- 🌊 量子場は仮想粒子の揺らぎに揺れ、これらの仮想粒子は非常に短時間しか存在せず、観測できません。
- 🔗 量子場論では、異なる場が共存し、粒子の異なるファミリーを構成し、それらの場には内部の対称性があり、時間とともに一定の量が保存されます。
- 🤝 量子場論は、場の相互作用を許可することにより、力がどのように生じるかを説明し、电磁力などの基本的な力を記述します。
- 🔍 量子場論は、特殊相対性理論の制約を満たす量子的宇宙の記述を可能にし、驚くべき精度で宇宙の現象を予測できます。
Q & A
量子力学はどのようにして粒子の位置を記述するのですか?
-量子力学では、粒子の位置は確定的ではなく、空間に分布し、その存在は多かれ少なかれの確率で表されます。これは粒子を確率の波と呼ばれるものとして記述します。
量子力学が説明できない状況とはどのようなものですか?
-量子力学は、時間の経過とともに粒子の数が変わる状況を説明することはできません。また、同じ種類の粒子が同じプロパティと動作を示す理由についても説明できません。
量子場論とは何ですか?
-量子場論は、量子力学と特殊相対性理論を調和させる新しい数学的枠組みです。これにより、粒子がどのようにして相互作用し、力が生じるのかを記述することができます。
空間時間とは何を表していますか?
-空間時間は、特殊相対性理論において宇宙の組織を表すものです。このビデオでは、2次元の空間と時間の次元を単純化して表現しています。
場とはどのような概念ですか?
-場は数学においては、空間時間全体を満たす流体のようなもので、各点には数値、ベクトル、またはその他のエキゾチックなオブジェクトが含まれています。
スピンとは何を意味していますか?
-スピンは、特殊相対性理論において、場の数学的オブジェクトが空間を回転させるとどのように見えるかを示すパラメーターです。
量子場とは何ですか?
-量子場は、時間の経過とともに複数の構成をとる可能性を持つ古典場を量子力学で扱ったもので、エネルギーの量子化された状態をもつことができます。
仮想粒子とは何ですか?
-仮想粒子は、量子場の揺らぎによって一時的に生成され、非常に短時間で存在し、観測することは厳密には不可能な粒子です。
標準模型とは何を意味していますか?
-標準模型は、粒子物理学において、宇宙の微观世界を記述する最も成功した枠組みであり、異なる粒子の家族を構成する複数の場のセットを指します。
量子場論はどのようにして力を説明するのですか?
-量子場論では、場同士が相互作用し、仮想粒子を介して運動量を交換することで力が生じる様子を説明しています。このプロセスは、電磁力などの力の根源を明らかにします。
量子場論はまだ完全な理論とは言えない理由は何ですか?
-量子場論は特殊相対性理論に満足するが、重力を記述する一般相対性理論と統一されておらず、宇宙の曲げを量子的レベルで説明する理論がまだ見つかっていないためです。
Outlines
🔬 量子场論の基礎
この段落では、量子場論の概念が説明されています。量子力学において粒子は確定的な位置を持たず、空間中に確率的な波の形で存在します。しかし、量子力学は粒子の数が時間とともに変わる状況や、同じ種類の粒子が同じ性質を共有する理由を説明することができません。そのため、特殊相対性理論と量子力学を統合する新しい数学的枠組みが必要となります。この枠組みにより、空の宇宙を構築し、そこに場を追加し始めます。場は数学的なオブジェクトで空間時を満たし、特殊相対性理論の対称性に従う必要があります。
🌌 量子場の構築と粒子の振る舞い
この段落では、特殊相対性理論の制約に従い、空間時を量子場で満たし始めます。量子場は古典的な場から量子化され、複数の状態を同時に取り得ます。この量子化により、エネルギーレベルを持つ量子場が得られ、粒子はその場の揺らぎとして存在します。また、仮想粒子と呼ばれる一時的な揺らぎも存在し、これらは非常に短い間だけ存在します。さらに、異なる粒子の種類が空間時の中に存在し、これらの粒子は特定の対称性を持つ内部構造を持っています。
💥 量子場の相互作用と力の発生
この段落では、量子場が相互作用を許すことでどのように力が生じるかが説明されています。特に、電子場と光子場の間の相互作用について焦点を当てています。電子が仮想光子を放出または吸収する簡単な相互作用を許すことで、電子が徐々に動くようになります。量子場はすべての可能なシナリオを同時に実現し、これらのシナリオの合成が物理システムの実際の進化を記述します。このようにして、量子場論は力が単純な対称性からどのように生じるかを説明します。
🌐 量子場論の限界と万物の理論への道
最後の段落では、量子場論が特殊相対性理論の制約を満たす量子的宇宙の記述を可能にしていること、そしてその限界について話しています。量子場論は驚くべき精度で宇宙の現象を予測することができますが、重力を記述する一般相対性理論と統合することはできません。ブラックホールの時間による蒸発などの結果はすでに計算されていますが、重力と量子を統合する万物の理論を求める研究はまだ続いています。
Mindmap
Keywords
💡量子力学
💡量子場論
💡空間時間
💡場
💡スピン
💡対称性
💡量子化
💡仮想粒子
💡標準模型
💡相互作用
Highlights
量子场论是量子力学和特殊相对论的结合,用于描述微观世界。
在微观尺度上,粒子的位置不是固定的,而是以概率波的形式分布在空间中。
量子力学无法描述粒子数量随时间变化的情况,如光子被电子吸收。
量子力学将每个粒子视为独立的,忽略了粒子家族之间的相似性。
为了解释电子等粒子的相同性质,需要建立一个新的数学框架。
量子场论通过引入场的概念,将粒子视为场的局部表现。
场是充满整个时空的数学对象,可以是数字、向量或其他更复杂的对象。
特殊相对论要求场中的数学对象必须遵守时空的对称性。
场中的数学对象根据自旋(spin)分类,如自旋为零的标量场和自旋为一的矢量场。
量子场论将经典场转变为量子场,允许场以多种配置存在。
量子场具有能量级,可以包含整数数量的能量量子,即粒子。
量子场还受到虚拟粒子的扰动,这些粒子短暂存在且无法直接观察。
标准模型是描述宇宙微观粒子内容的集合,包括各种自旋的场。
量子场论通过允许场之间的相互作用,解释了力的产生。
通过简单的对称性,量子场论解释了粒子如何通过交换虚拟粒子来相互作用。
量子场论是构建模型宇宙的数学配方,它预测了宇宙的微观现象。
尽管量子场论非常成功,但它仍然无法与描述引力的广义相对论统一。
科学家仍在寻找一个统一理论,以解释空间时间的弯曲和量子现象。
Transcripts
[Music]
welcome back to science clique
today quantum field theory
unlike a marble which has a definite
position
at the microscopic scale a particle does
not really have a position
its presence is distributed throughout
space with more or less probability
this description of particles as waves
of probability
is called quantum mechanics
quantum mechanics allows us to describe
the evolution of a particle
over time
however this description as effective as
it is
fails to take into account two
considerations
firstly quantum mechanics cannot
describe situations where the number of
particles
varies over time however in nature we
often observe that particles can appear
or disappear
like when a photon gets absorbed by an
electron in an atom
secondly quantum mechanics treats each
particle independently
however within a family of particles
such as electrons
all exhibit the same properties and
behaviors
how is it that an electron coming from
the far reaches of the cosmos
has exactly the same mass or charge as
an electron in an apple
to answer this question we will have to
build a new mathematical framework
a more general description that
reconciles quantum mechanics with
special relativity
we will construct the most successful
framework available for describing the
microscopic world
in this video we build together quantum
field theory
to begin with let's start with an empty
universe
relativity teaches us that the fabric of
the universe is space-time
to simplify we will represent only two
dimensions of space
as well as the dimension of time
we now want to fill our universe with
content mata
we saw previously that all particles of
the same type
for example all electrons appear
perfectly identical
as if they were only local
manifestations of a single
underlying object which would fill the
whole universe
a field to add content to our universe
we will therefore start by adding a
field
[Music]
in mathematics a field is like a fluid
which fills all space time
each point of which is populated by a
mathematical object
it can be a field of numbers vectors
or other more exotic objects
that said special relativity imposes
some restrictions
it forces us to respect certain
symmetries which correspond to the
geometry of space-time
symmetries of translation rotation
or changing frame of reference
[Music]
these symmetries are only respected by
certain mathematical objects
and we can classify them with a
parameter spin
the simplest objects that we can use are
numbers
we give them spin zero because when we
rotate space around a number
it does not vary
vectors on the other hand indicate a
direction in space
their appearance depends on the
orientation in which they are observed
we assign them spin one because when we
rotate space by a full turn
a vector also describes a full turn
finally relativity also allows other
more exotic objects
and in particular spinners which have
spin one half
you have to make two turns around a
spinner for it to come back to its
initial state
[Music]
all these mathematical objects seem very
abstract
and some are difficult to understand but
technically they all obey the symmetries
of relativity
and are therefore potential candidates
with which we could fill our universe
[Music]
in addition to imposing the types of
objects that are allowed
space-time symmetries also set
restrictions on the way
objects behave inside the field
each symmetry forces the field to
respect the conservation of certain
quantity
over time to obey relativity
our field must respect the conservation
of energy
momentum angular momentum
and velocity of the centre of mass
moreover the mathematical objects
themselves can contain symmetries of
their own
if we decide to form a field with
complex numbers for example
they exhibit an internal symmetry which
implies the conservation of another
quantity over time
related to the very nature of complex
numbers
the electric charge
[Music]
at this stage we have a space time which
we have filled with a field
which satisfies all the restrictions
imposed by special relativity
but our goal is to describe the
microscopic world
so it's time to turn our field into a
quantum field
[Music]
in quantum mechanics to transform a
classical object into a quantum object
we allowed it to adopt several positions
at the same time
with more or less probability
[Music]
similarly to transform a classical field
into a quantum field
we allow it to adopt several
configurations
multiple ways it can evolve with more or
less importance
[Music]
over time our field evolves as a
superposition
of all possible scenarios
transitioning from a classical field to
a quantum field
results in a very interesting property
just like an electron in atom has
well-defined energy levels
[Music]
a quantum field also has energy levels
it can only contain an integer number of
disturbances
quanta of energy that can appear or
disappear
these are particles
much like a wave on the surface of water
a particle is simply a disturbance which
propagates within the field
[Music]
a quantum field is also agitated by
fluctuations
which keep popping in and out of
existence these are called virtual
particles
these virtual particles exist only very
briefly
so that it is strictly impossible to
observe them
[Music]
step by step our model universe is
getting closer to reality
we now describe a space-time filled with
a quantum field
inside which move disturbances particles
in a soup of fluctuations virtual
particles
in our universe several fields coexist
and constitute different families of
particles
some are vector fields spin 1 and the
particles they contain
are photons z and w bosons and gluons
others are fields of spinners spin one
half
they are the fermions that make up
matter quarks
electrons muons tau particles and
neutrinos
finally there is a field of spin zero
the higgs field
among all these fields most have
internal symmetries
which provide them with quantities that
are conserved over time
charges which distinguish their
particles between several versions
we saw previously that fields formed
with complex numbers
have asymmetry which gives them their
electric charge
this symmetry allows us to distinguish
two versions of the particles
one with positive charge the other with
negative charge
this is anti-matter in a way
the anti-particle is the complex
conjugate
of the ordinary particle
other fields also have more exotic
symmetries
the quark fields for example exhibit a
symmetry which assigns them another
charge
the colour charge which must also be
conserved over time
and that allows us to separate quarks
into three versions
red green and blue
the set of all these fields that make up
the content of our universe
is the standard model of particle
physics
to this day this is the most successful
description of our universe on the
microscopic scale
[Music]
our model universe now contains the same
particles as our real universe
however it still isn't realistic indeed
the symmetries of space time
force all particles to move in straight
lines forever
independently one from the other
to finally complete our model all we
have to do is add one more fundamental
ingredient
we need to allow these fields to
interact with each other
[Music]
to understand let's focus on one of the
simplest interactions
between the photon field and the
electron field
we will allow an electron to emit or
absorb a virtual photon
and vice versa allowing only this simple
interaction will have drastic
consequences
for instance in the following situation
we start with two electrons motionless
over time the two electrons progress
towards the future
at first one might think that the two
electrons remain motionless indefinitely
but that would be forgetting that our
electrons are constantly moving through
the photon field
with which we allowed them to interact
[Music]
we saw that a quantum field realizes all
possible
evolutions at the same time
in a way each evolution describes a
scenario
and in some of these scenarios the
electrons will interact
with the photon field
[Music]
in this scenario for example the
electron emits a virtual
photon at a certain instant which
carries away
part of its momentum and the virtual
photon is absorbed a little later
by the other electron
[Music]
in this other scenario the electrons
exchange this time
two photons
[Music]
or again in this third more complex
scenario
the electron emits a virtual photon
which is converted into a pair of
virtual electron and positron
that inhalate together into a virtual
photon
which finally ends up absorbed by the
second electron
by exchanging part of their momentum
carried by virtual particles
the two electrons will in some scenarios
get closer
and in others get further apart
now consider the following analogy on a
guitar a
string can vibrate with different
frequencies each of which corresponds to
a pure
sound but when we pluck the string
it starts to vibrate in a superposition
of all these frequencies with more or
less amplitude
and the synthesis of all these pure
sounds together with different
amplitudes
is what makes the total sound produced
by the string
similarly a quantum field evolves
according to every possible scenario
with more or less amplitude and it is
the synthesis of all these scenarios
together
that describe the real evolution of the
physical system
in particular in our example when we add
up all these possibilities
we observe that overall our two
electrons are more and more deflected
they feel a force repelling them because
of the exchanges of virtual photons
this is the electromagnetic force
and if instead we had started with an
electron and a positron
of opposite charge the amplitudes of the
different scenarios would have been
different
resulting this time in an overall
attraction force
[Music]
by allowing particles to interact and
exchange momentum
quantum field theory explains how forces
arise from simple symmetries
the symmetries of the fields which make
up our universe
to conclude quantum field theory is a
mathematical recipe
for building a model universe we start
with an empty space-time
which we fill with quantum fields that
satisfy the symmetries
of special relativity quantum field
theory thus makes it possible to
construct a quantum description of our
universe which satisfies the constraints
imposed by relativity by allowing fields
to interact with each other
this theory makes it possible to predict
with astounding precision
the phenomena that govern our universe
according to quantum field theory the
evolution of our universe is described
as the synthesis of
all possible scenarios at the
microscopic scale
that being said this description remains
incomplete
as even though it satisfies special
relativity quantum field theory cannot
be unified
with general relativity which describes
gravitation by the curvature of
space-time
some results of the theory can already
be calculated in curved space times
such as the prediction that black holes
evaporate over time
however scientists are still looking for
a unified theory
that would explain microscopically why
space-time gets curved
and would reconcile the infinitely large
with the infinitely small
gravity with quantum a theory
of everything
[Music]
you
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