## What is quantum field theory in simple terms?

Definition of quantum field theory : a theory in physics: the interaction of two separate physical systems (such as particles) is attributed to a field that extends from one to the other and is manifested in a particle exchange between the two systems.

## What is quantum field theory Weinberg?

Weinberg was a master of quantum field theory, a branch of physics born from applying the rules of quantum mechanics to the electromagnetic field, which sees a particle — the photon —as a “quantized” excitation of the field.

**Is quantum field theory real?**

Over the past century, quantum field theory has proved to be the single most sweeping and successful physical theory ever invented. But quantum field theory, or QFT, is indisputably incomplete. Neither physicists nor mathematicians know exactly what makes a quantum field theory a quantum field theory.

**Is Fock space separable?**

Fock Space is separable. Thermal Field theories have non-separable Hilbert spaces, but Fock space is separable.

### Why is quantum field theory necessary?

You need a quantum field theory to successfully describe the interactions between not merely particles and particle or particles and fields, but between fields and fields as well.

### Why is quantum field theory so hard?

The Heisenberg uncertainty relation means that a quantum field cannot sit still. Instead, it froths and boils, a bubbling soup of particles and anti-particles, constantly created and destroyed. This complexity is what makes quantum field theory hard. Even nothingness is difficult to understand in quantum field theory.

**Why do we need quantum field theory?**

**Who discovered the quantum field theory?**

In particle physics, the history of quantum field theory starts with its creation by Paul Dirac, when he attempted to quantize the electromagnetic field in the late 1920s. Major advances in the theory were made in the 1940s and 1950s, and led to the introduction of renormalized quantum electrodynamics (QED).

## Why quantum field theory is wrong?

It means all these particles are desctibed as a “single letter” like electron. So quantum field theory cannot express each particle as an actual object. Unless quantum field theory can explain actual, concrete state of each particle, it is completely useless and meaningless for us, forever.

## Will physics ever be complete?

As long as such mysteries remain — and there are others — the work of physics will not be complete. The aim of physics is to understand in a precise, mathematical way all manifestation of matter and energy in the universe — and we have barely started to explore this infinitude of possibilities.

**Are Fock states orthogonal?**

be an orthonormal basis of states in the underlying one-particle Hilbert space. Fock states often form the most convenient basis of a Fock space.

**What is the difference between first and second quantization?**

The first quantization is the quantization of classical lagrangian particle(s) mechanics。 The second quantization is the quantization of classical field theory like electromagnetic field, dirac field and so on.

### What is Fock space in quantum mechanics?

Definition. The Fock space is the (Hilbert) direct sum of tensor products of copies of a single-particle Hilbert space Here , the complex scalars, consists of the states corresponding to no particles, the states of one particle, the states of two identical particles etc.

### Is Fock space the direct sum of all Hilbert spaces?

In a book, it says, Fock space is defined as the direct sum of all $n$-body Hilbert Space: $$F=H^0\\bigoplus H^1\\bigoplus \\bigoplus H^N$$ Does it mean that it is just “collecting”/”adding” all the states in each Hilbert space? I am learning 2nd quantization, that’s why I put this in Physics instead of math.

**What is the general state in the Fock space?**

The general state in a Fock space is a linear combination of product states. A state that cannot be written as a convex sum of product states is called an entangled state . , it must be borne in mind that in quantum mechanics identical particles are indistinguishable. In the same Fock space, all particles are identical.

**How do you find the total Fock space?**

So far we have defined the Fock space ℱ N pertaining to a fixed number N of identical particles. We can formally construct the total Fock space by performing a direct sum, (14.23) ℱ = ⊕ N = 0 ∞ ℱ N.

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