Science Myths

Myth #1: The Maxwellian Velocity Distribution can be measured directly with a flow of a model gas.

In many physics laboratories in schools and universities, the experiment "Maxwellian Velocity Distribution" can be found with a model gas of spheres and measuring the velocity distribution at a flow of the model gas:

The documentation of that product can be found here and examples can be found here and here and here.

REALITY:

The ensemble of the model gas has (nearly) a Maxwellian Velocity Distribution. But only the flow of the pushed out balls is being measured in this experiment, not the ensemble! Because a physical flow is, by definition, density times velocity (v), the velocity distribution of the pushed out balls is the Maxwellian Distribution times v, also called Modified Maxwellian Distribution. This multiplication with v is also necessary for calculating the flow rate .
The correct name of the experiment would therefore be "Modified Maxwellian Distribution".
This is also described and verified with many experimental results, e. g. in the journal Physical Review, Volume 99, Number 4, August 15, 1955, pages 1314-1321 (article "Velocity Distributions in Pottasium and Thallium Atomic Beams" from R. C. Miller and P. Kusch).
See also the book "Fundamentals of Statistical and Thermal Physics" from Frederick Reif, Chapter 7.12 (Effusion).
In the german version of this book, "Statistische Physik und Theorie der Wärme", from Frederick Reif, 3. Aufl., ISBN 311011383X, you can find it on page 322.

Myth #2: The three-body problem is insoluble.

In many physics books and scripts we can find the statement that the three-body problem is insoluble (except of only few special cases), because Poincaré said so in the late 1800s.
Examples can be found here and here.

REALITY:

Poincaré did only show that with the mathematical methods he used, an analytic solution for 3-body problem can not be found. Several time later, in 1912, the necessary mathematical methods where developed and the Finnish mathematician Karl Fritiof Sundman proved that there exists an analytically solution: Sundman's theorem for the 3-body problem.
This result was generalised to the case of n>3 bodies by Q. Wang in the 1990s: The global solution of the n-body problem.

Myth #3: The second law of thermodynamics is necessary for defining the arrow of time.

In many physics books and scripts we can find the statement that the second law of thermodynamics and entropy are necessary even for the Arrow of time.
Examples can be found here, here and here.

REALITY:

It's true that an arrow of time can be defined via the second law, but only statistical. And since 1998 it is known that time-reversal symmetry is broken in neutral kaons, which means that neutral kaons do show the arrow of time: http://physicsweb.org/articles/world/11/12/3
and http://bulletin.cern.ch/9847/art1/Text_E.html.
It is also known that certain subatomic interactions involving the weak nuclear force do violate the conservation of parity. According to the CPT Theorem, this means they are also time irreversible, like the neutral kaons.

Long before 1998 it was known that Quantum mechanics defines an arrow of time e. g. by a free particle, because in Quantum mechanics a free particle is a deliquescent wave packet:

|ψ(x, t)|² = 1/(d *sqrt(2 *π(1+Δ²))) * exp(-(x-v*t)/(2*d²(1+Δ²)))

with

Δ = t *h/(4*π*m*d²) .

This Gaussian wave packet has the position average

<x>=v*t

and the position uncertainty

Δx=d*sqrt(1+Δ²)

in non-relativistic Quantum mechanics.
So in Quantum mechanics the motion of the center of gravity of a free particle is time-reversal but the deliquescing is not because it depends on t². Therefore time-reversion, which means changing t to -t does not change the deliquescing, because t²=(-t)² .
Another point is that, because of the Uncertainty principle, the reversal of the deliquescing is not possible in Quantum mechanics.
That's why the deliquescing of the wave function of a free particle defines a Quantum mechanic arrow of time.

Another example is the Quantum decoherence, which is also irreversible.

In classical physics there are similar time arrows. See for example the Rayleigh Lighttrap, directional couplers and Circulator .

Myth #4: Sometimes a kilo is 1000 and sometimes it is 1024.

A kilo, abbreviated k, usually means 1000 but it is often used as the factor 1024, e. g. here, here and for the file size under a Microsoft operating system.
Another example is this list of definitons, from http://imgs.xkcd.com/comics/kilobyte.png :

REALITY:

First: It's nonsense to set a kilo to 1000 or to 1024, denpending on the mood, the daytime or other things!
The kilo is and has always been a dezimal SI prefix which is 1000 by definition: http://en.wikipedia.org/wiki/Kilo .
Since 1954 the kilo, mega, giga, tera etc. are part of the International System of Units (SI) .
Before this international standard, the kilo was used long before e. g. for the Kilogram and the kilo was defined by the metric system, in the proclamation on June 22, 1799: http://en.wikipedia.org/wiki/Metric_system .

Since 1999 the international standard IEC 60027-2 is the official and legal standard for the binary prefixes and defines kibi, abbreviated ki, as 1024. This standard also defines mebi (=1,048,576), gibi (=1,073,741,824), tebi (=1,099,511,627,776) etc..
Before IEC 60027-2 and the kibi, 1024 was written as capitalized prefix K, not k, to make clear that it is not a kilo; setting k to 1024 is therefore completely wrong!
Although for exact countable integer things like bits and bytes it does not make sense to say 1024 is nearly 1000, in many old software and even in 2007 actual operating systems from Microsoft you can find the bug that binary prefixes are confused with decimal prefixes but hardware manufacturers do use the prefixes correct. An example is the capacity of this 120 GB hard disk drive, where you can find the correct equation
1 GB=1,000,000,000 Bytes
in the middle of the sticker:

Science Myths

Myth #1: The Maxwellian Velocity Distribution can be measured directly with a flow of a model gas.

REALITY:

Myth #2: The three-body problem is insoluble.

REALITY:

Myth #3: The second law of thermodynamics is necessary for defining the arrow of time.

REALITY:

Myth #4: Sometimes a kilo is 1000 and sometimes it is 1024.

REALITY:

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