280 views

Why are there $1 / 1.602176634 \times 10^{-19}$ electrons in a coulomb?

Why that exact number of electrons in one coulomb? who decided it? there is nothing wrong with the number, it just seems slightly messy. Why didn't the scientific community just settle on an easier ...
540 views

There are plans to develop a better definition of a “second”. How does the current definition fall short?

The current definition of a second is stated here and I found a presentation on the BIPM site which discusses plans to change to a "better" definition of a second. You can find the presentation here. ...
221 views

Redefinition of everything on May 20th, 2019 [closed]

A couple of issues: So after May 20th, 2019, what exactly will be the defined value of $\hbar$? What will be the defined number of elementary charges in a Coulomb? Then $\mu_0$ and $\epsilon_0$ will ...
144 views

Does the death of Kilogram ($kg$) affect us in any means in our day to day life? [closed]

Recently, the sleek cylinder of platinum-iridium metal has been discarded and the kilogram is set to be redefined along with ampere for electricity and Kelvin for temperature. Hereafter the Kilogram ...
114 views

Why is the kilogram defined using Earth's gravity? [closed]

Since there are variations of $g$ depending on location on Earth's surface, why not use a reproducible lab experiment using a vertical axis centrifugal balance, and say that one kg is defined by ...
588 views

How to distinguish between the spectrum of an atom in motion and the one of a scaled atom?

Galaxies are moving dragged by the space expansion. When atoms are in motion the doppler effect will shift the spectra of the emitted photons. The proton-to-electron mass ratio, $\frac{m_e}{m_p}$ ...
215 views

Is absolute zero still 0 Kelvin?

Following the recent decision to change the definition of SI units, I understand that Kelvin is no longer defined in terms of the number 1/273.16. Does that mean that absolute zero is no longer ...
295 views

SI Base Unit definition of mass - obsolete?

According to the formal definition of the SI Base unit of mass, the kilogram, it is stated that "The kilogram is the unit of mass; it is equal to the mass of the international prototype of the ...
415 views

How accurately can you count electrons?

I read that with modern technology they can now shoot one electron at a time. Can you tell me how accurately it is possible to count charges, how it is made and how they did this in the past? How ...
354 views

Why must the kilogram standard be based on a kilogram mass object?

Inspired by the accepted answer to a question about the Avogadro Project, why must an object used to define a new standard for the kilogram have a mass of one full kilogram? If a smaller mass were ...
344 views

How explain this perturbing equation about the 43 arcseconds?

The planetary orbits have been studied as ellipses but the solar system is in motion in relation to the distant stars. Their path is along the tip of an helix and the ecliptic plane is a convenient ...
111 views

Why is the kilogram the last SI unit which is defined in terms of a physical prototype? [duplicate]

All elementary SI units, except the kilogram, have been redefined depending of a physical constant. However kilogram still depends on the International Prototype Kilogram. Why is this? Is there no ...
222 views

How can a Lego version of a Kibble balance measure the Planck constant?

As the picture shows below [][1] in a Kibble balance, one can drop out the measurement uncertainty of $B$ (magnetic flux intensity) and $L$ (length of coil) by the use of two modes, force mode and ...
What is the mass of $N_A$ atoms of carbon-12?
With the recent redefinition of the kilogram, what is the mass of $N_A$ (Avogadro's constant) of carbon-12 atoms? $N_A$ was defined as exactly 6.02214076×$10^{23}$ atoms. Then how close would the ...
I am specifically interested in the following constants because being a student these are some of the most common constants that I face: $R$ (universal gas constant) Stefan constant Permeability of ...