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Answer of the Most Important Unsettled Question of Physical Theory in 20th Century—Can Schrödinger Equation Describe Transition Processes

Junhoa Zhang Shantou University Shantou People’s Republic of China

Abstract

Quantum mechanics take the sum of first finite order approximate solutions of time-dependent perturbation to substitute the exact solution, it will produce the error. How much is this error? However people do not find up for arbitrary N and the exact solution , so quantum mechanics can not answer this question. Therefore this ‘unknown error’ is as a premise of all theoretical conclusions of quantum mechanics for the transition processes. This problem is relative to the question. Can we really use the Schrödinger equation to describe the transition processes? So it is the most important unsettling problem of physical theory in 20th century. All of physical theory cannot avoid the strictly mathematical inference.

We find out the time-dependent perturbation approximate solution for arbitrary order and the exact solution . Then we can prove that: (1) In the neighborhood of energy conservation, the series is divergent. The basic error of quantum mechanics is using the sum of the first finite order approximate solutions to substitute the exact solution in this divergent region. It leads to an infinite error. So the Fermi’s golden rule is not a mathematically reasonable inference of the Schrödinger equation (2) The transition probability per unit time deduced from the exact solution of Schrödinger equation cannot describe the transition processes.

 

 

(1) The most important unsettled question of physical theory in 20th century

 

Quantum mechanics deems that, we can use the Schrödinger equation

(1)

to describe the variance of the system with time, where

(2)

We may write the as the product of time independent with a time dependent factor . Quantum mechanics only discusses two types , they are

(3)

and

(4)

The eigenvalues of are discrete or continuous. We shall discuss for each case. In discrete case, according to quantum mechanics, suppose

(5)

Then the Schrödinger equation may be written as

(6)

The time-dependent perturbation theory supposes that

(7)

and uses the approximate equations

(8)

(9)

to substitute the exact equation (6).

So far, people only find the few order approximate solutions of (7). We do not find out for arbitrary order. The only way is to substitute the exact solution by the sum of first finite order approximate solutions

(10)

and to use this sum to describe the transition processes.

The problem is that, whether the may be abandoned? From the point of physics, if the abandoned part is large then the experimental error, then we cannot obtain any conclusion from the comparison between the sum of first finite order approximate solutions with experimental results. In this case, the words “Schrödinger equation may describe the transition processes” would be meaningless. From the point of mathematics, is the function of energy . Only in the convergent range of series, for , we can find a number M , that the relation

(11)

is satisfied. What is for arbitrary order? What is the exact solution ? In which range is the series divergent? These questions are relative to that, can the equation of quantum mechanics describe the transition processes? So it is the most important unsettled question of physical theory.

 

(2) Discussion in the case in which the eigenvalues of are discrete and the time factor is

 

The equations (6) and (9) contain , it means that we discuss in the discrete case. We shall solve the Schrödinger equation and its approximate equations in the range .

 

(2-1) Expression of for arbitrary

 

Quantum mechanics found out the first finite order time dependent perturbation approximate solutions. The forms of first and second order approximate solutions are simple. However it is difficult to look for the general form of the approximate solution from them. The purpose of this section is to find the another form of the approximate solution, it can help us to seek the general form of the high order approximate solution.

Considering the stationary state equation

(12)

(13)

Let us use the stationary state perturbation solution

(14)

(15)

to substitute in the expression of , then it is easy to discover the general form of the time dependent perturbation approximate solution. and satisfies the stationary state approximate equations

(16)

(17)

where satisfies the orthonormalization condition

(18)

In appendix A we prove that the order time dependent perturbation approximate solutions may be expressed as

(19)

(20)

(21)

The first order of time dependent perturbation approximate solution deduced by quantum mechanics does not contain the term. This term is

(22)

It is just the term in Eq. (20). So you see the result give by quantum mechanics is incomplete. The incompleteness in the low order approximate solution will influence the calculation in the high order approximate solution.

According to Eqs.(19) —(21), you may easy to discover that the general form for arbitrary N order time dependent perturbation approximate solution is

(23)

where the coefficients are

(24)

(25)

(26)

We shall take in the latter calculation, so we have

(27)

According to Eqs.(24)—(26), you may guess that the general form of must be

(28)

Because the first order time dependent perturbation approximate solution deduced by quantum mechanics is incomplete, then the high order approximate solution will do not contain the term relative to . For comparing, let us consider the first term of Eq.(23),

(29)

This formula contains all of orders approximate solution deduced by quantum mechanics. For example, in the case of , we obtain

(30)

from Eq.(29). The second order approximate solution deduced by quantum mechanics is

(31)

The difference between these two equations is due to that quantum mechanics neglects the contribution of in calculation the first order approximate solution. The simple formula of Eq.(29) not only contain all order approximate solutions that they have been found out. It is also correct in the case for arbitrary order.

Other coefficients are

(32)

(33)

(34)

The general form is

(35)

where is the function of , it is not relative to .The recurrence relation is

(36)

(37)

is the sum of many terms, each term contains factors of

(38)

The total of approximate order is

(39)

Summarizing above results, the expression of for arbitrary order is

We prove this formula in the case , but it is only a guess in the high order case. However the task focus on the proposition, if Eq.(40) is correct for order, try to prove that it is correct for order. We prove this proposition in appendix B.

 

(2-2) The expression of the exact solution

 

According to Eq.(7), the exact solution is

Calculating this expression, we may obtain

(42)

You can find the calculating process in appendix C. The opposite process is to expand presented in Eq.(42) by using the stationary-state perturbation approximation, we may obtain the different order of time-dependent perturbation approximate solution .

Finally we test that is the exact solution of the Schrödinger equation in appendix D. It means that this conclusion is correct not only in the convergent intervals, but also correct in the divergent intervals of the series.

 

(2-3) The error of time-dependent perturbation approximation

 

Now we affirm three points:

(i) Eq.(42) is satisfied the Schrödinger equation and the special initial   condition;

(ii) Expanding the coefficient presented in according to the stationary

state perturbation, and classifying according to the different approximate order we get

;

(iii) is satisfied the time-dependent perturbation approximate equation and special initial condition.

They are the basic to discuss the core of unsettled question—in which range is the series divergent?

The exact solution must be expressed by the solution of stationary state equation . Substituting the stationary state perturbation approximate solution into presented in the exact solution, we shall obtain the different order approximations of the time–dependent perturbation method . Therefore, the divergent intervals of the time-dependent perturbation approach and the one of the stationary state perturbation approach are identical. Quantum mechanics pointed out that the divergent interval of the stationary state perturbation series is . So it must be the divergent interval of the time-dependent perturbation series. It means that, for each , no matter how much order approach solutions we take into account, the relation

does not satisfy in the divergent interval. We cannot use the sum of first finite order of time-dependent perturbation solutions to substitute the exact solution. The error of time-dependent perturbation method is using to substitute for calculating the transition probability in the divergent range . Let us examine the first-order approximation of the time-dependent perturbation

is the -component of an unit vector. Therefore

(44)

and Eq.(43) can only be used in the region .

According to quantum mechanics, we have

(45)

(46)

There are two questions. First, the premise of this section is that we discuss in the discrete case. Quantum mechanics changes to discuss the continuous case and simply substitutes Eq.(45) with Eq.(46). Is this reasonable? We shall discuss this question in the next section. Second, the transition probability deduced from the perturbation approximation is correct only in the region ; the fault is in . If we use the expression of the first order stationary state perturbed approach in the region , the error is

If .

Quantum mechanics discuss the relation between with . And pointed out there is a peak of function in , this peak of function is just deduced from the error factor . If , the high of peak tends to infinite,and the breadth of the peak tends to zero, the discussed function becomes function. However if

, the whole main peak of function is in the divergent region of the perturbation approximate series. The problem is that it is under these two conditions, , and

 

 

 

 

Fig.1 The relation between with , where I is the

divergent region of the time-dependent perturbation approximate series.

 

, that quantum mechanics obtains

(47)

from Eq.(46). Fermi called it as the golden rule. Of course, if this formula is correct, then someone can find a suitable to be identical with the experimental value , but mathematically Fermi’s golden rule is not a reasonable conclusion from the Schrödinger equation.

 

(2-4) Transition probability per unit time deduced from the exact solution

 

According to quantum mechanics, the transition probability per unit time is defined as

(48)

Note that

(49)

It means that is the -component of a unit vector, and is the -component of another unit vector. The expression

is the product of two unit vectors, so

(50)

Finally we obtain

(51)

This is the result deduced from the exact solution of Schrödinger equation (1) in the case. This result cannot be used to describe the transition processes.

We summarize the discussion in the discrete case:

  1. The substance of the time-dependent perturbation approximation is to expand presenting the expression of according to the stationary-state perturbation approach..
  2. The convergent interval of the stationary-state perturbation approach is , this region is also the convergent interval of the time-dependent perturbation approach..
  3. The sum of the first finite order perturbation approximate solutions may be used to substitute the exact solution only in the convergent interval. The fundamental error of the time-dependent perturbation approach is using the sum of the first finite order approximate solutions to calculate the transition probability in the divergent interval . Mathematically Fermi’s golden rule is not a reasonable conclusion from the Schrödinger equation in the discrete case.
  4. People use the sum of first finite order perturbation approximate solutions to substitute the exact solution. It only caused by that they did not find out the approximate solution for arbitraryorder. When we find out and , then we have not any reason to use the sum of first finite order perturbation approximate solutions to substitute the exact solution. The pity is that, the transition probability per unit time deduced from the exact solution of the Schrödinger equation is zero in the discrete case, it cannot be used to describe the transition processes.

 

(3) Discussion in the case in which the eigenvalues of are continuous and the time factor is

In the continuous case, the discrete variable must change to continuous variable , the summation must change to the integration, and presented in the discrete case must change to , the others are same as in the discrete case. This kind of variation cannot give the difference result.

 

(3-1) Exact solution

 

In the continuous case the Schrödinger equation has the form

(52)

The initial condition can be expressed in the form

(53)

If the initial condition takes the form of Eq.(53), then at the probability of the system in the region is

(54)

We can prove that the exact solution of the Schrödinger equation (52) in the special initial condition is

(55)

where are the eigenvalue and eigenfunction of the stationary-state equation

(56)

respectively.

At the same time, the eigenfunctions satisfy the orthonormalization conditions

(57)

(58)

(3-2) Equivalence of the time-dependent perturbation approximation and the stationary-state perturbation approximation

 

According to the stationary-state perturbation approximation method, suppose that

,

(59)

where satisfy a set of equations

(60)

and satisfy the orthonormalization condition

(61)

(62)

Inserting the stationary-state perturbation approach Eq.(59) into Eq.(55), and decomposing them according to the approximate order, we obtain

(63)

where

The relations between with are same as in the discrete case.

are the solution of the time-dependent perturbation approximate equations

(65)

The approximate solutions satisfy the initial conditions

(66)

(67)

The time-dependent perturbation approximation is equivalent to the stationary-state perturbation approximation in this case.

 

(3-3) Error of deduction of transition probability from the time-dependent perturbation approach

 

The zeroth and first-order stationary-state perturbation approximations are

,

(68)

Even if we can use the first order time-dependent perturbation approximation, in the continuous case the correct expression of the first order approximation must be

(69)

However, at , the probability of the system in is.

Then the relative transition probability per unit time is

(70)

It cannot describe the transition processes.

 

(3-4) Deduction of the transition probability from the exact solution

The transition probability in is a relative probability. It is defined as

(71)

In this equation the denominator is

(72)

the numerator is

(73)

In the continuous case, satisfies the orthonormalization condition (57). Then is the -component of a normalization vector, and is the -component of another normalization vector. The expression

is the product of two normalization vectors, so

(74)

The transition probability per unit time is

(75)

In the continuous case the transition probability per unit time deduced from the exact solution of the Schrödinger equation is still zero.

 

(4) Discussion in the case in which the time factor is and the eigenvalues of are discrete

 

Quantum mechanics uses

(76)

to describe the electron transition from one energy level to another due to the impact of the electromagnetic field. In general, only the discrete is discussed. The Schrödinger equation has the form

where

(78)

Suppose

(79)

where is the probability amplitude of the state in which there is an electron in and photons of energy . If at , the system is in the state then

(80)

According to Eq.(77) and Eq.(80), we get

(81)

which , are the solution of the stationary-state equation

(82)

Suppose

(83)

then Eq.(82) may be rewritten in the form

(84)

At the same time, meets the orthonormalization conditions of the eigenfunctions:

(85)

(86)

Obviously, the exact solutions solved under the cases and have the identical mathematical structure. The results in Sec. 2 are still applicable in this case.

 

Conclusion

  1. In the cases in which the time factors are or , the eigenvalues of are discrete or continuous, the process to deduce the transition probability per unit time from time-dependent perturbation approximation contains a basic mathematical mistake. It is using the sum of first finite order approximate solutions to substitute the exact solution for calculating the transition probability in the divergent range—the neighborhood of energy conservation. Fermi’s golden rule is not the mathematically reasonable deductive inference from the Schrödinger equation.
  2. The transition probability per unit time deduced from the exact solution of the Schrödinger equation cannot be used to describe time-dependent processes.

 

(5) Other equations in quantum mechanics

 

There are other equations in quantum mechanics, such as the unitary matrix equation

(87)

and the Dyson’s equation (method of Green’s function)

(88)

The unitary matrix equation is suited to extend to quantization of field. We have discussed these two equations. The result is same as the Schrödinger equation. The exact solution cannot be used to describe the time dependent processes.

The basic task of quantum mechanics is to describe the stationary motion of the system and the time dependent processes. If the exact solution cannot be used to describe the time dependent processes, then we must reconsider the basic point and the basic picture of quantum mechanics.

 

 

Appendix A: Deducing of first finite orders time dependent perturbation approximate solutions

 

Quantum mechanics found out the first finite order time dependent perturbation solutions, but it is difficult to look for the general form of the high order solution from them. We introduce a new method to calculate the approximate solution and obtain a new expression. It is more complex then the usual way, but you can easy to look for the general form of arbitrary order approximate solution from them.

We shall use the stationary state perturbation equations

(A1)

(A2)

(A3)

The normalization conditions of eigenfunctions are

(A4)

(A5)

(A6)

According to Eqs.(A1) and (A4), we get

(A7)

The zeroth order time dependent perturbation approximate equation is

(A8)

and the special initial condition is

(A9)

According to these two equations we obtain

(A10)

where

(A11)

Using this form is only for to expand the result to the high order approximate solution. We always take

(A12)

in the latter calculation.

The first order time dependent perturbation approximate equation is

(A13)

According to Eq. (A2), we obtain

(A14)

We add a term to the second line of this expression. According to Eq. (A1), the contribution of this term is zero. We shall explain it in latter. The definition of is

(A15)

Then Eq.(A13) may be written as

(A16)

Suppose that has the form

(A17)

Differentiating the Eq.(A17) we get

(A18)

Comparing Eq. (A16) with Eq. (A18), we obtain

(A19)

(A20)

So

(A21)

(A22)

The first order time dependent perturbation approximate solution deduced from quantum mechanics does not contain the term , this term is

(A23)

It is corresponding to the term in Eq. (A17).

According to Eq.(A17),

(A24)

therefore satisfies the special initial condition. It is the reason that we add a term in Eq.(A14).

The second order time dependent perturbation approximate equation is

(A25)

where

(A26)

We add a term

(A27)

in Eq. (A26). The definition of is

(A28)

In addition we have

(A29)

Therefore we obtain

(A30)

The right side of this expression is sum for all . When , it has the form . So the expression of contains the term of . So we suppose that the solution has the form

(A31)

Therefore

Comparing Eq.(A30) with Eq.(A32), we get

(A33)

(A34)

(A35)

Finally we find

(A36)

(A37)

(A38)

According to Eq. (A31)

(A39)

satisfies the initial condition.

Now we collect above results,

(A10)

(A17)

(A31)

The coefficients decompose two sets, one set is , and another set is . For the set , we have

(A11)

(A22)

(A36)

therefore we may image that

(A40)

where

(A41)

The another set is

(A21)

(A38)

(A37)

Then we may image that, in the case

(A42)

where is only the function of . The first few functions are

(A43)

(A44)

(A45)

We shall obtain more knowledge of in the latter,

(A46)

(A47)

is the sum of many terms, each term contains factors of ,

The sum of approximate order is

(A48)

 

 

 

Appendix B: The time-dependent perturbation approximate solution is Eq.(40) for arbitrary N order

 

Now let us prove that the time-dependent perturbation approximate solution is

 

by the substitutive method, where

(B1)

(B2)

(B3)

(B4)

Firstly, we prove a preparative formula

(B5)

The stationary state equation is
(B6)
Its perturbation approximate equations are
(B7)
(B8)
So we get
(B9)
We obtain that
the first term of (B9) (B10)


because of
(B11)
The second term of (B9) is relative to . The region of two sums is in 

Fig.2.

 

Fig. 2 The region of two sums is on the triangle (containing the boundary).

We may exchange two sums by this way



and obtain that
the second term of (B9) (B12)
Then the relation
 (B5)
is correct.
Now we use the inductive method to prove the time-dependent perturbation approximate solution for arbitrary N order is

(40)
If , (40) may be simplified as
(B13)
It is the solution of zeroth order time-dependent perturbation equation and satisfies the special initial condition. If , (40) may be simplified as

(B14)
It is the solution of the first order time-dependent perturbation equation and satisfies the initial condition.
Supposing that the solution of N order perturbation equation is (40), we shall prove that the solution of N+1 order perturbation equation has the form same as (40).


(B15)

The first term of (B15) =



A factor in second term of (B15) is


Fig.3 Exchanging two sums in above expression, .

Where
(B16)
Therefore,
the second term of (B15)



Substituting above results into (B15), we get
(B17)
Now let us prove that the expression of is
(B18)
In fact,
(B19)
So (B17) satisfies the N+1 order perturbation approximate equation. In addition,
(B20)
Therefore satisfies the special initial condition. So we prove that, if (40) is correct for N order, then it must be correct for (N+1) order. We have prove this expression is correct for N=0,1orders. So it must be correct for arbitrary N order. 

Appendix C: The expression of exact solution

We have obtain

(C1)


Fig. 4 Exchanging two sums in Eq.(C1), .

According to the time-dependent perturbation approximate method, the exact solution is defined as
(C2)
Now the task is to calculate the sum in this expression. Notice that the contribution of second term of Eq.(C2) in the case is zero. Therefore
(C3)
Suppose
(C4)
then we have 
(C5)
Using this relation, (C2) may be written as
(C6)

Fig.5 Exchanging two sums in Eq.(C6), .

We prove that the relation
(C7)
is correct.
According to (B2), we get
(C8)
so (C7) is correct for . Suppose that (C7) is correct for , then we have 
(C9)
Therefore (C7) is correct for . The conclusion is that the relation (C7) is correct for arbitrary .
According to Eq.(B1),
(C10)
Substituting Eqs.(C7) and (C10) into Eq.(C6), we finally obtain
(C11)
It is just the exact solution of Schrödinger equation. From this deducing process, we conversely prove that, using the stationary state perturbation method to expand in exact solution, we may obtain the different order of time-dependent solutions.

Appendix D: Test the exact solution of Schrödinger equation

Now we test that, is
(D1)
the exact solution of Schrödinger equation? Does it satisfy the initial condition? In fact,
(D2)
Therefore Eq.(D1) satisfies the Schrödinger equation. In addition, if 
(D3)
It is the special initial condition.

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Fig.5


References
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