Hw3313621364

H. Arabshahi, A. Haji Mohammadi Fariman and M. Jafari Matehkolaee / International Journal
of Engineering Research and Applications (IJERA) ISSN: 2248-9622
www.ijera.com Vol. 3, Issue 3, May-Jun 2013, pp.1362-1364
1362 | P a g e
Proof of the Energy-Time uncertainty principle in Powerful
Statement
H. Arabshahi, A. Haji Mohammadi Fariman and M. Jafari Matehkolaee
1
Department of Physics, Payame Noor University, Tehran, Iran
2
Sama Technical and Vocational Training College, Islamic Azad University, Sari Branch, Sari, Iran
ABSTRACT
In this paper we have tried to perform a
comprehensive summery of Energy-Time
uncertainty principle. At first we review the
history of uncertainty principle then the most
well-known arguments between Einstein and
Bohr. Our main aim is to provide an acceptable
relationship for Energy-Time uncertainty
principle and proof to it.
I. Introduction
The momentum-position uncertainty
principle has an energy-time analog,
.Though this must be a different kind of
relationship to the momentum-position one, because
t is not a dynamical variable, so this can't have
anything to do with non- commutation.
There are many quantum mechanics books and
papers about energy-time uncertainty principle.
After reading many of them we asked ourselves: just
what is the energy time uncertainty principle,
anyhow? After looking in many quantum mechanics
papers and books, We was astonished to find (this is
2013!) that only one of them [7] managed to give an
acceptable statement of it, where by “acceptable”
we mean an inequality in which all variables have a
mathematical definition.
Section II gives a history of uncertainty principles
and section III gives a careful review on energy-
time uncertainty principle and finally we present a
detailed proof for Thirring’s view.
II. History of uncertainty principle
This section gives a history of uncertainty
principles, including an amusing debunking of
common myths about the Bohr-Einstein box debate.
For another history quite complementary to ours,
see [1].
The uncertainty principle expresses the
physical content of quantum theory in a qualitative
way [2]. The uncertainty principle was first
proposed by Heisenberg in 1927. It basically states
that is not possible to specify exactly and
simultaneously the values of both members of a pair
of physical variables which describe the behavior of
an atomic system.
In a sense the principle can also be seen as
a type of constraint. The members of a pair are
canonically conjugate to each other in a Hamiltonian
way. The most well- known example is the
coordinate x of a particle (position in one
dimension) and its corresponding momentum
component Px :
(1)
Another example is the angular momentum
component of a particle and the angular position
in the perpendicular (xy) plane:
(2)
In classical mechanics these extreme
situations complement each other and both variables
can be determined simultaneously. Both variables
are needed to fully describe the system under
consideration. In quantum theory, (1) states that one
cannot precisely determine a component of
momentum of a particle without loosing all
information of the corresponding position
component at a specific time. If the in- between
extremes case is considered, the product of the
uncertainty in position and the uncertainty in the
corresponding momentum must numerically be
equal to, at least, /2 To understand the physical
meaning of the uncertainty principle, Bohr in 1928
stated the complementary principle. This principle
shows the fundamental limits on the classical
concept that a system's behavior can be described
independently of the observation procedure. The
complementary principle states that "atomic
phenomena cannot be described with the
completeness demanded by classical dynamics" [2].
Basically the principle states that experimental
apparatus cannot be used to determine a
measurement more precisely than the limit given by
the uncertainty principle. In a sense when a
measurement is done to determine the value of one
of a pair of canonically conjugate variables, the
second variable experiences a shift in value. This
shift cannot be calculated exactly without interfering
with the measurement of the
Among the most amusing historical developments in
the early history of quantum mechanics were the
oft-recounted debates between A.Einstein and
N.Bohr. The legends associated with these debates
are positively permeated with the same aura as the
famous story of George Washington and the Cherry
Tree. Einstein at the 1930 Solvay conference [3], [4]
presented to Bohr the following attack on quantum
mechanics via the energy time uncertainty principle.
Keep in mind that in 1930, it was still 15 years
before the first precise statement of this principle
had been made [5], so Bohr and Einstein were

1363 | P a g e
arguing about an issue neither understood. (They
both thought the uncertainty principle was
and with the interpretations of the 's
the same as in the principle. This
interpretation has never been justified, and also note
that the coefficient on the right hand side is also
unjustified, at least in [1].) Einstein considered a
box being weighed by a spring scale and containing
photons. A cuckoo-clock mechanism mounted on
the box opens a door on the box's side for a time
duration t, specified extremely precisely, and with a
precision apparently independent of any quantity
having to do with photon energies. The weight of
the box before and after the measurement seems to
be measurable extremely precisely, and hence, since
, the energy of the escaping photons is
deducible extremely precisely. Hence we get
(where denote uncertainties in the
values of t and of the energy E of the photons that
escaped through the door) arbitrarily small, refuting
quantum mechanics. Of course, of the three
formulations of the energy-time principle given
here, and Finkel's [6], none of them pertain to
uncertainty in the time lapse at all, so this entire idea
of Einstein's was based on a false premise. But
neither Einstein nor Bohr were aware of that, and so
both thought this was a tremendously dangerous
attack on the foundations of quantum mechanics. So
then (the usual tale proceeds) Bohr after great effort
refuted Einstein’s attack by invoking general
relativity (!), as follows the uncertainty in the
vertical position z of the spring scale obeys
. Einstein presumably wants
, where g is the
acceleration of gravity. But now, the clock mounted
on the box, according to general relativity, differs by
from the time on a clock attached rigidly to the
earth, where . Hence our knowledge of the
time lapse will suffer from an uncertainty of order
, saving the uncertainty principle
and quantum mechanics. The Fairy tale
concludes: Einstein was so stunned at this use of his
own theory of general relativity against him, that he
conceded defeat. Actually, Bohr’s counterattack,
although startling, had two fatal flaws. First, we do
not see what has to do
with . We could agree only to
perform weightings after exponentially damping the
box’s motion by placing it in a bath of viscous oil;
any uncertainties in the weighing would then seem
to be of a fixed magnitude exponentially
independent of anything else. (The box would be in
a minimum uncertainty state after the damping,
roughly.) second, neither gravitational time dilation
nor need have anything to do with the case. This
is because Einstein could instead have measured the
mass of the box with an electric field (after charging
the box with a known amount of charge). The
capacitor plates generating the electric field could
have been superconductively shorted during the
door-cycling but charged to 1 volt for the
weightings- say by connection to an arbitrary
enormous external capacitor bank providing a 1 volt
reference. Thus, both steps in Bohr's argumentation
depended on an extremely specific scenario and
don't impact on even slightly altered scenarios much
less the whole of physics.
III. The energy Time uncertainty
principle
In trying to change time, as the classical
external parameter, into an observable, one cannot
deduce the time-energy uncertainty relation:
2
t E   ; (3)
Where t = time , E = energy
From kinematical point of view, as time
does not belong to the algebra of observables [8]. In
spite of this, (1) is generally regarded as being true.
The relation (3), unlike other canonical pairs, is not
the consequence of fundamental quantum
incomplementarity of two canonical variables. The
time-energy uncertainty relation is very different to
the standard quantum uncertainty relation, such as
the position momentum one. The precise meaning of
the time-energy relation is still not exactly known.
The problem lies in the fact that one cannot give the
precise meaning to the quantity t . This is because
time is not a standard quantum mechanical
observable associated with an Hermitian operator. If
such an operator canonically conjugate to the
Hamiltonian did exist, then, t could be defined
conventionally and the uncertainty principle could
be applied to the physical quantity corresponding to
the time operator.
Of course there have been a few attempts in
the literature to formulate and prove energy time
uncertainty relations. But we start to theorem of
Mandelstam and Tamm[5].
We know that for any observable O that not depend
explicitly on time
Now suppose we choose A=O and B=H(O and H
are operator), where H is the Hamiltonian. From
we get
(4)
Now we define and define
(5)

1364 | P a g e
Then by the combine above equations we obtain (3).
This is the energy time uncertainty principle where
is the amount of time it takes for the expectation
value of the observable O to change by one standard
deviation as follows
(6)
If is small then the rate of change of all
observables must be very gradual or, put the other
way around, if any observable is changing rapidly
then the uncertainty in the energy must be large.
Thirring’s [7] actually gives an inequality in which
every term in the formula has a mathematical
definition. Here we present a detailed proof.
Suppose is a wavefunction evolving with time t,
to where H is a Hamiltonian operator.
Suppose the probability that an energy
measurements on would yield a value in an
energy interval of width , is . Then
Proof
Suppose is a wave function so that, with time it
changes into , which we obtain by applying
the time-evolution operator. The probability
measure on after time of t is as .
Then life time of Ψ is equal to
(7)
By use the Fourier transform and Parseval's equality
we have
In above relation the second integral shows that
frequency space and . So we
calculate the Fourier transform function of
then we can write
Thus we get
(8)
Now we are concerned with the extent to which the
state at a later time t is similar to the state at t=0, we
therefore construct the inner product between the
two states at different times
So we get the correlation amplitude , as
following
The correlation amplitude that starts with unity at
t=0 to decrease in magnitude with time. The
probability measure energy on at is equal to
According to Cauchy-Schwarz inequality (for
integrals) we get
Then
Since So we get
then by the (8) we obtain
References
[1] E.A.Gislason, N.H.Sabelli, J.W.Wood,
New form of the time-energy uncertainty
relation, Phys.Rev.A31,4(1985) 2078-
2081.
[2] Schiff, L.1., "Quantum Mechanics",
McGraw-Hill, (1968).
[3] N.Bohr: Essays 1958-1962 on atomic
physics and human knowledge, Wiley
1963.
[4] N.Bohr: Discussion with Einstein on
epistemological problems in atomic
physics, in Albert Einstein: philosopher-
scientist ( ed. By P.A. Schilpp ) Open
Court Press, 1982 reprint.
[5] L.Mandelstam & Ig. Tamm, The
uncertainty relation between energy and
time in quantum mechanics, J.Phys. USSR
9 (1945) 249-254.
[6] R.W.Finkel, Generalized uncertainty
relation, Phys.Rev, A 35,4(1987) 1486-
1489.
[7] [7]. W.Thirring: A course in mathematical
physics, 4 volumes Springer (1st
edition
1981,2nd
edition 1986).
[8] [8]. Muga, J.G.,R.Sala and J.Palao,
Superlattices Microstrcut.,833(1998).

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