ON SPIN
STATISTICS THEOREM.
A friend wanted to understand 'Bose -Einstein
statistics’ in a simpler format. This is my reply to him.
'Bose -Einstein statistics’ follows from something
called the Spin-Statistics Theorem. It requires relativity, to derive the
Spin-Statistics Theorem. There are lots of attempts to justify the result
without relativity, but they do not work in the mathematical formalism. As I
have repeatedly written citing Prashastapaada, relativity is a wrong
description of reality and there is much misunderstanding about the nature of bosons
and fermions. One can Google “Anti-Relativity” and find huge support for my
above statement.
It is said that exchanging the position of two
fermions will change the sign of the wave function, while the wave function for
bosons will remain the same. Why does this happen and what does spin has to do
with it? No one understands. Some say Bosons’ are particles whose wavefunction
is symmetric under such an exchange or permutation, so if we swap the particles,
the wavefunction does not change. Fermions are particles whose wavefunction is
antisymmetric, so under such a swap the wavefunction gets a minus sign, meaning
that the amplitude for two identical fermions to occupy the same state must be
zero. This is the Pauli Exclusion Principle: two identical fermions cannot
occupy the same state. This rule does not hold for bosons. Too confusing.
Others say, Bosons’ wavefunctions do not change
sign when you rotate them 360 degrees, while fermions’ wavefunctions do change
sign when you rotate them 360 degrees. What happens if we interchange two
bosons or fermions? Also, why fermions' wave functions change sign upon
rotation of 360 degrees. Secondly, why two identical particles interchanged is
equivalent to one being rotated by 360 degrees?
To understand the problem, one must understand what
is spin and what is the nature of fermions and bosons. Think of a small
cylindrical pipe and a candle. Place both on the table and rotate. When you
rotate the candle by 360 degrees, it comes back to its original position. That
is, by spinning once, it reverts to its original position. This is an example
of Spin 1. Now rotate the cylindrical pipe. You do not have to rotate it by 360
degrees, it appears to come back to its original position after rotating 180
degrees – ½ of one spin. This is an example of Spin 1/2.
Now think of a glass and water filled in it. Water
needs a container – here the glass tumbler. Overturn the glass by 180 degrees.
All the water is displaced – occupy space in ‘another container’ – may be of
different shape including the flat surface where it spreads. But if you rotate
the empty tumbler by 360 degrees, it returns to its original position without
being displaced. The solid glass tumbler behaves like a boson and the liquid water
behaves like fermions.
Electricity is the flow of electrons and behaves
like a fluid. You can picture these as a fish in water. The water surrounds the
fish. We observe something only by contrasting its motion or radiation with its
background. We observe the fish only because it radiates different wavelengths
than water. We cannot differentiate one water molecule or a drop of water from
another, because they radiate the same wavelength. If the fish moves, it
creates a tip or a wave-front, which we could differentiate from the background.
Similarly, what we call bosons (including electrons), are nothing but a part of
the “electron sea”, in which some radiation from the protons (like the fish)
creates a wave-front. We call each such wave front electrons.
For this reason, one cannot predict the position of
an electron, but when one measures it, one finds it in a fixed position. How
can one measure unless he/she first observe the wave-front? One cannot measure
something without perceiving it first. “Scientists” up turn this logic and say
that, though they cannot predict the exact location of the electron, an
electron is always found in a place when it is measured. This way, they fool
everyone with incomprehensible statements and “mathematical structures”.
There is no weirdness in the quantum world. I can
explain each quantum phenomena with macro equivalents. Modern science needs
rewriting and it must not be done by the “Scientists”, but rational people who
do not fantasize.
The fallacy of modern science is imprecision in the
name of precision. They do not define any term precisely, but give an
operational definition, which is subject to change according to the context.
Thus, they can use the same term to imply opposite features and make laymen
believe that science is super magic and if one believes in God, then He is a
magician.
What is space? Both space and time arise from our
notions of sequence and interval (paratwaaparatwa). The intervals between
ordered sequence of objects is called space and those of events (changes in
objects) is called time. Since intervals have no markers to describe them, they
are described through the alternative mechanism (vikalpana) of the boundary
objects or events. Without boundary objects or events, space or time is
meaningless.
Einstein defines space as that which we measure by
a measuring rod. But it does not define space. It simply substitutes the word “space”
by “which we measure by a measuring rod”. But what it is that is measured? No
answer. From this he switches to manifold (such as four dimensional spacetime
manifold), which is a collection of points forming a certain kind of set, such
as those of a topologically closed surface or an analogue of this in three or
more dimensions. This confuses everyone and they continue to extend this to a
long array of different spaces and sub-spaces starting with Minkowsky
spacetime, De-Sitter space and Hilbert space, etc. in n-dimensions without
precisely defining dimension. If they precisely define dimension, all these
“theories” including string theory or the other variant M-Theory would fall
disgracefully as absurd. ALL modern scientists use these without defining space,
time and dimension. If they define these precisely, ALL their theories will
fall.
Now the other lie of modern scientists! Space or
space-time is NOT expanding, as it is not evident in local scales. It is
observable only in galactic cluster scales. Some “scientists” explain this by
comparing space with a balloon and the stars and galaxies as rigid spots on it.
If the balloon expands, the spots remain fixed – they say. But in that case,
the balloon would burst. However, the universe is not bursting. Since space is
the interval between objects and is described by the boundary objects only, it
was indescribable before structure formation. However, since structure
formation was an event, time existed before space. Thus, we can say space is
emergent in time (kaalaat vyaapaka uchyate). Thus, time, as we know it, is
emergent (aksharaat samjaayate kaalah) from the big-bang or big-bounce (minus
its extensions and mathematics).
The fundamental nature of time is cyclic: measuring
events from being as cause to becoming as effect, growth through accumulation,
transformation through harmonious accumulation, transmutation due to
dis-harmonious accumulation, and finally, change of form through disintegration
and assimilation with other elements. This continues as a flow – a river
flowing towards the sea (nadeeva prabhavaat kaachit). These cycles take two
forms: individual (mrityu - death) and universal (yama – big crunch minus
mathematics and extensions). The midpoint is the condition of maximum entropy. When
all individual cycles become co-terminus at one point, they resemble the state
before creation – beyond the quark-gluon plasma, which are derivatives of the
primordial soup - but with some inherent instability. This inherent instability
generates inertia of motion (vega) that moves at the fastest speed across the
expanse in the state of near equilibrium. The background at rest responds by generating
inertia of restoration (sthitisthaapaka) that decelerates the inertia of motion
through something like a bow-shock effect (a boat being pushed back against its
motion due to resistance by river water) to finally bring it to a halt (Maya).
This cuts off a big spherical volume (hiranmaya anda), which is closed from the
background at its periphery (naimishaaranya). This volume is called the
universe (Brahmaanda).
From the boundary of the universe, the impulse of
the initial forward motion reverses due to reconnection effect (like that seen
behind a boat or in the magnetosphere). This incoming force (dhaaraa) leads to
couplings that finally leads to structure creation (Jaayaa), due to
accumulation in various proportions. I can describe the detailed mechanism
separately. This process repeats continuously leading to slowing down the speed
of light over time. This can explain the so-called dark-energy without esoteric
and fancy ideas.
Like everything else in the universe, it itself is
spinning around its axis. For this reason, the galactic clusters appear to move
away from us (red-shift) at times to come closer (blue-shift) at other times,
just like planets in the Solar system appear to move fast (atichaara) at times
to become retrograde (vakra) at other times. There is no mystery, but lack of
mastery in explaining physics.
Sequence is related to inter-se arrangement or
relative positioning, which gives rise to direction. Without sequence,
indicating a direction would not be possible. Interval is related to the inter-se
arrangement of position, i.e., how far the objects are positioned from each
other. It gives rise to dimension. Without interval, it would be impossible to
define dimension.
Both space and time arise from our NOTIONS of
sequence and interval means, it can only be perceived by using the concepts of sequence
and interval. Perception is always about some external object. Thus, it is
question of how we perceive it and not whether it is related to individual or
universal perception.
All perceptions including that of space and time
are sensory constructs. Its processing and comparison with memory are
individual processes. Thus, we perceive the same thing differently – neither
higher nor lower, as there is no yardstick for that. The individual perception
is the notion for that individual. Intellectual disability is not a universal
term. A person, who lacks the mechanism for perception of interval, cannot
perceive space or distance, because distance is the interval of an object from
some reference point.
Sequences could be ordered or random. Both space
and time are ordered sequences. This gives time its “arrow”, because even
undoing something is “another event” and not “undoing the event”. However,
space is not bound by this principle. Hence there are different directions and
no “arrow”.
If I pull your hand only, your body will also be
pulled in the same direction, though inertia will try to resist the motion.
Thus, local conditions affect global conditions – may be in a chaotic manner
like the butterfly effect, where each step of the effect is not perceptible,
though accumulated effects in the long run are perceptible. Expansion of the
universe was postulated based on something called “red-shift”. Now, we have
seen galactic mergers and collisions, which are not possible if the universe is
expanding. Further, “blue shift” has been observed, which indicates that some
galaxies are coming closer. Hence there is no reason to clutch to the earlier
idea that the universe is expanding, even after the evidence showing its
contrary, and when other cosmological phenomena like the planetary motions give
a suitable explanation.
Analogy (udaaharana) is a thing which is comparable
to something else in significant respects - a comparison between one thing and
another, typically for the purpose of explanation or clarification
(saadharmodaaharana). If it cannot explain or clarify the concept that is
sought to be explained or clarified, it cannot be called an analogy.
Modern scientists cannot answer: “Into *WHAT* (if
anything) is spacetime supposed to expand?” Thus, they say that is not
important – I do not understand how it is not important.
Like everything else in the universe, it itself is
spinning around its axis. By it, I mean the galactic center.
The galactic clusters appear to move away from us
(red-shift) at times to come closer (blue-shift) at other times. This has been
experimentally verified. However, our experimentation is highly insignificant
in cosmic time scales. To observe both the Red-shift and Blue-shift for the
same galaxies will requires a minimum of few million years.
Firstly, there is no book that is directly ascribed
to Charvak. Even there is doubt as to whether there was a person by that name
(some say he is the brother of Brihashpati) or it was a collection of palatable
(charu) statements (vak). We gets bits of his views scattered in different
places quoted by others. The terms used by you are used in Nyaya and the
Buddhist philosophies, which are abridged versions of Nyaya. Diungnaga and
Vasubandhu had discussed these in their books.
HETU (हेतुः): 1)
In Vaisheshika, it is used as a determinant (ज्ञापकः).
This can be of two types: true determinant (सद् हेतुः)
or false determinant (हेत्वाभासः). 2)
Cause (कारणम् or उत्पादकम्). 3. Independent inducer for an action (स्वतन्त्र प्रेरयन्). 4) An object that fulfills the need (फलसाधनयोग्यः पदार्थः). This is the Nyaya view that
requires an analogy, based on which a statement is sought to be proved (उदाहरणसाधर्म्यात् साध्यसाधनं हेतुः). 5) Outcome (फलम्). 6) A type of simile (अर्थालङ्कारविशेष). 7) One of the
five components of research methodology (न्यायावयवः).
SADHYA (साध्यम्). 1) Object
to be accomplished or determined by
applying logic (साधनीयम्). In your example, proving the
existence of fire from smoke is Sadhya. 2) One of its variations is called
Paksha (पक्षः) – When
only a partial exposition in conformity with the proposition is presented (साध्यार्हः प्रतिज्ञेयः पक्षः). Here, the analogy given does not
necessarily conform to the final statement. 3) The process of naming or
describing an action (लिङ्गसंख्यानन्वयिनी क्रिया). 4) One of the various groups based on the
gravitational effect (गणदेवता विशेषः). 5) A specific division of time (मुहुर्तनाम). 6) Capable of
being easily performed (स्वानुकुलताग्राहकः पदार्थः).
VYAPTI (व्याप्तिः). It is a
type of special relation (सम्बन्धविशेषः). It may extend one relationship or property or
it may exclude such relationship or property. It is useful for drawing
inference, which can be used to present one’s stand point (paksha). It is a
vast subject with five branches. Gangesha has written a big book called Vyapti
Panchak on this subject.
ON CERTITUDE (सिद्धान्त)
The issue of certitude can be approached from two
different perspectives: 1) absolute perspective on the statement, which can
also be called the abstract perspective, and 2) a more particular or as a
special case. Let us discuss the absolute perspective first.
The word certitude is generally understood as: absolute
certainty or conviction that something is “surely” the case. Thus, negative
certitude would imply: absolute certainty or conviction that something is
“surely” not the case. In either case, there is an “absolute certainty or
conviction” or “surety” that one’s knowledge about something is validated by
proof, aided by logic. Thus, the validity or otherwise of certitude – negative
or positive – boils down to the validity of the proof submitted to justify it
(siddhaanta). This can be examined from four perspectives.
1) Everyone
says something conclusively or with certitude only when he/she thinks it is “surely”
true or useful in the particular context, which implies, ruling out its
improbability. If the proof or logic advanced in its support of certain
philosophy is accepted by all (there are several such concepts where all
philosophers agree unanimously) and countered by none – the Holistic Truth or
the Big Unitary Truth, then the certitude is positive and universal (sarva
tantra siddhaanta).
2) There
are philosophies, which some consider as valid, whereas others contest its
validity. If both groups could sit together and iron out the differences, then
it becomes positive and universal certitude. But before such resolution, the
competing philosophies remain as contrary or negative certitude for each other
(pratitantra siddhaanta), because a third person cannot be certain, which
philosophy is correct. They only “surely” know that one must be correct and the
other wrong. Here, every theory has its own truth and truth standards, which
cannot fairly be judged in the light of rival standards.
3) There
are certain foundational concepts, which, once established, leads to prove
another concept. To give one example, the functioning of senses and consciousness
are correlated. The senses are different and each perform a specific task –
eyes can only see, ears can only hear, etc. But we perceive every sensory
impulse uniformly as “I know…(I am seeing, hearing, smelling, tasting,
touching)”. We may touch the thing we see, though the senses are different.
Thus, the “knower” must be different from the “known” or the object of
knowledge. But till the knower or Consciousness is established (i.e. a person
is conscious), the individual senses have no meaning. The certitude like this,
i.e., statements like “only conscious beings can utilize senses” is called
foundational certitude (adhikarana siddhaanta).
4) There
may be cases where we do not have a clear stand on any subject, though other
philosophies have a specific stand on it. We can temporarily accept that
proposition as true and then apply logic to determine related aspects. In such
a case, if we come to a conclusion based on an uncertain proposition, the
certitude is called directed certitude (abhyupagama siddhaanta).
I am unable to make any sense of it. Kindly remove
my doubts by explaining your comments.
a) How
does your statement at a) harmonize with the measurement problem of QM? Zeno
effect is a wrong description of reality, where the principle of measurement
cannot be applied. Measurement is a comparison between similars, out of which
one is the unit, with which the other is scaled up or down. Hence, measurement
always returns scalar quantities. In Zeno effect, reduction of remaining
distance by half is compared with a constant velocity in each step. Both being
finite quantities, the answer should be finite and not infinite. Otherwise the
definition of motion itself would be wrong. Any reduction must imply a scalar
quantity by which the objects are scaled down. This would necessitate a gradual
change in the system. If “conscious entity would be a sequence of state
function reductions”, the state cannot remain invariant. Your comparison of
this with Maya may not be proper. Mostly, people have no understanding of Maya,
which, by definition, is related to measurement and superposition – not
illusion. Some, who do not know about its mechanism, speak vaguely about it.
b) )
In zero energy states, there cannot be any motion, as all motion requires
energy. Time evolution implies change of state in time. Thus, there cannot be
zero energy states – these can only be states at equilibrium – or zero net
energy. There is much confusion about super-position of states. Suppose in a
sea beach, two waves come from two angular directions, where the crest of one
interacts with the trough of the other, so that both flatten out. Before their
interaction, we could differentiate between the two waves. After the
interaction, we can never identify each wave – they have gone into a superposition
of states. This is not a uniquely quantum phenomenon, but is happening
regularly every moment in the universe. Water from the ocean goes up to come
down as rains. We die and our bodies are assimilated in Earth or the atmosphere
to reappear in different combinations. It is our inability to point out the
“position” of something that we knew earlier – it has a different position now,
may be by distribution in parts scattered all over, making it impossible for us
to specify its earlier specific position, but known to be present in different
positions by part simultaneously. For this reason, it is called superposition
of states. Light cone is fiction. If a light pulse expand in time in a two
dimensional field, it would generate concentric circles of higher radius in the
same plane – not in different planes (that would make it three dimensional, but
unlike the images given by Hawking and others, which show it as conic
sections). In three spatial dimensions, the light pulse expanding in time,
would make it concentric spheres of increasing radius – not cones. “Opposite
boundaries of causal diamond (CD) obtained as intersection of future and part
directed light-cones” are nothing more than meaningless words. Thus, kindly
explain what exactly you wanted to convey, because, rest of your comments are
based on these.
c) Death,
just like birth, is a feature of time evolution related to superposition of
states. Time, like space, arises from our concept of sequence and interval. The
ordered internals of two sequential objects is space and that of events is
time. Since intervals have no markers to describe them, these are described by
using alternative symbolism of the boundary objects and events. The boundary
objects and events are not space and time, but are the digitized versions of
arbitrarily chosen segments of analog space and time. Unlike space, time is
cyclic. Existence involves six stages from “being” as a cause to “becoming” as
effect, to “growth” by accumulation to “transformation” by accumulation of harmonious
elements to “transmutation” by accumulation of non-harmonious elements to
“change of form” by disintegration and dispersal. This is one cycle for any
object. There are infinite interrelated cycles. The beginning of a cycle is
called its birth and the end is called death. But these do not define life.
There is no proof to show that “Self re-incarnates at opposite boundary as
time-reversed self”. Rather your statement raises questions on re-incarnation,
arrow of time, and self. What is the proof for re-incarnation and time
reversal? WHAT is “SELF”. What are sub-selves? What is geometric time? What is
sleep?
There is much confusion about freewill. It is
limited freedom of thought and consequent action. All our actions are guided by
two factors: 1) any external impulse that stimulates our senses, and 2) our
memory that retains the earlier experiences in yes/no/neutral format. If the
incoming impulse is harmonious with our stored memory of experience, we get
attached to the object. If it is not harmonious, we are repelled by it. If it
is the first time or indeterminate experience, we ignore it. Thus, our reaction
is shaped by a) our past experience that shapes our mental preparedness b) our
ability to respond physically to the mental preparedness. Freewill is subject
to these limitations. In case of conceptual issues, it is our ability to
understand natural principles based on our early experience (knowledge) and
relate it to other aspects of the physical world, guide our thinking process.
Mostly people approach the same subject from different angles based on their
past experience, which operates on the principle of inertia of limited motion.
This inertia is known as the thought. This is continuously updated. That might
be called the evolutionary approach.
The idea of Truth must have some perfect
correlation to the state of reality. Truth is based on some central theme,
around which, we build a field of related experiences, which is confined by our
“total knowledge”. This is the same as in the quantum world: a nucleus,
surrounded by an intra-nucleic field, and confined by the electron sea. Hence,
it is not correct to say that reality prevents us from acquiring such
knowledge. Suppose we see a rope in the darkness and mistaken it for a snake.
We may not have the knowledge of the rope, but we must have knowledge of the
snake. If we start from their and examine it closely, the motionlessness would
first give us the impression of a dead snake. Then if we get bold and examine
it from close quarters, we can finally come to the conclusion that it is not a
snake, but something else, to which we give a name. Later we can have knowledge
about the rope. Here we must differentiate between two types of “total
knowledge” – individual and universal. Whatever we come across, if we have a
knowledge about its reality – conceptual and functional mechanism that is
perceivable and communicable – it is “individual total knowledge”. The maximum
extent of this “total knowledge” is Omniscience.
Regarding "probabilities are quantifying OUR
degree of UNCERTAINTY about reality", there cannot be any standard candle.
The effects can be devastating (the 1 % probability of a bullet hitting a
person) or marginal or negligible (99% probability of getting a few rotten
wheats in a sack of wheats). In the former case, the 1% probability can become
vital (or interesting), whereas in the latter case, even 99% probability is
trivial. The same applies to scientific research. Most of our so-called
theories are fallacious or are based on unproved or non-existent concepts or
particles. The list is never ending, one of which related to the so-called dark
energy is dubbed the biggest mismatch in history. Modern science thrives only
on technology. Here even there is no probability of 1% of the “theories” standing
the test of scientific proof. Scientists cover is up under the cloak of
incomprehensibility and reductionism – and the latest trend of cocktail
science. Knowledge is never new, because it is our ability to understand some
existing function. It is always a discovery.
If meta-truth means the descriptive properties of
terms such as "good", "bad", "right", and
"wrong" do not stand subject to universal truth conditions, but only
to societal convention and personal preference, then you are correct. What is good
for one can be bad for the other. These are relative. But there are a few
universal truths like death for everything that was born, seasonal changes,
etc. These are neither good nor bad universally. To that extent, your
statement: “Reality … requires some sort of balance between order and chaos at
all levels (both physical and abstract), which seems to demand of us successive
levels of both humility and acceptance of diversity in ways that may not be at
all comfortable”, is correct.
Though you are talking sensibly, are you not mixing
two things? When you talk of numbers, we have to differentiate between the
concept of numbers and its application. Number is a property of all substances,
by which we differentiate between similars. If there are no similars, it is
one. If there are similars, it is many, which can be 2,3,4,…n, depending upon
the sequential perception of “one’s”. The number game applicable to many. But
can it be applied to something like consciousness? The objects of our knowledge
may be different, but in all such perceptions, the knowledge: “I know ….”
Remains invariant. Without the common “I know ….”, there can be no meaning to
anything.
When you talk about the pixels or colored dots, you
are talking about the process of the “many”. But unless one possesses the
“eyes”, you cannot interpret it. You analyze the external impulse in the brain
and decide what you want to do. But as I have explained earlier while
discussing freewill, you are really not independent, but are guided by your memory
of past experiences and physical capabilities. You are also telling the same
thing in a different language. The only difference is you are mixing up brain
and the consciousness. Functioning of the brain is a conscious process, but
brain is not the “consciousness”. There is a difference between the knower, the
known and the mechanism of knowledge. You are talking of the last two, but
leaving out the first.
Does “quantum mechanics chipping away at one side,
and AI and virtual reality approaching from a completely different paradigm
space”? I have shown while discussing truth that both have a similar format.
Only we have to see it in the contextual perspective. “Complexity theory,
maximal computational complexity, and notions like density matrices” etc. are
related to mechanism of observation or knowledge. There may be “a great many limits to our
ability to ‘know’ anything at any level beyond some sort of ‘useful
approximation’ relevant to the context”. But even there, the “I know ….” Part
remains invariant.
“Science, logic, computation, abstraction”; do not
change the knower or the object to be known. Humility “that accepts a sort of
fundamental ignorance that no AGI (Artifical General Intelligence) is a sign of
higher intelligence. Non-computable
approximations are working arrangements within our limitations.
But does the description “one spec of dust” has any
meaning in isolation? You must differentiate dust from everything else to make
any sense for the word “dust” (differentiation from dissimilars) and differentiate
all other dust specs from the “one” you are talking about (differentiation from
similars). Thus, your perception depends upon these two differentiation (there
is also the differentiation of parts from the whole). Eyes and light are only
subsidiary instruments for perception of objects. For example, consider
something placed in a room. If one is blind or there is no light, one cannot
perceive anything. But if there is light and the person has healthy eyes, he/she
can see clearly and describe such object. Mere placement of objects before our
eyes cannot ensure perception – or information. This is my scientific training.
Can you count 10^10 molecules at a time? No. We
count one by one. We may make units of thousand or million or billion in this
process. Then we have a mental picture of the total unit. That was only we
could count or know or measure 10^10 molecules. That is the only scientific
explanation. It applies for everything universally – be they molecules, atoms,
nucleons or quarks. We never utilize the full capacity of our brain, but use
only a small fraction of its total capacity. That is our inability – bot
brain’s failure.
How do you “take a snapshot of all the atoms in our
bodies, and blow it up to a size we can see”? Magnification distorts. We
observe only the present at here-now. Can we meet our ancestors or progenies if
we move fast enough? This is fiction – not science. Does the pulse of light
that radiated by a galaxy a billion light years away reach us undisturbed by
anything in its flight path? Not likely. Then how can we say that we are
looking at the past? How does relative speed affect perception? In the
laboratory, we measure wavelength of light. Since light moves at constant
speed, while our instruments are stationary, should we apply length contraction
to the wavelength? In that case, the result will be zero or infinity depending
upon how you interpret it. Will that be scientifically correct? My 50 years of
experience in this field tells me NO. Could we take a movie of a single active
enzyme site within one of our cells, for just one second of real time, then
slow it down enough so that we could actually see the movement of the water
molecules? The mismatch you say is proof enough for its scientific validity.
Your view that “to know something means simply to
have some sort of approximation that is useful in context” is a practical one
and is often used by everyone.
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