Albert Einstein is perhaps the most famous scientist of this century. One of his most
well-known accomplishments is the formula
Despite its familiarity, many people don't really understand what it means. We hope this explanation will help!
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One of Einstein's great insights was to
realize that matter and energy are really different forms of the same
thing.
Matter can be turned into energy, and energy into matter.
For example, consider a simple hydrogen atom, basically composed of a single proton. This subatomic
particle
has
a mass of
0.000 000 000 000 000 000 000 000 001 672 kg
This is a tiny mass indeed. But in everyday quantities of matter there are a lot
of atoms! For instance, in one
kilogram of pure water, the mass of
hydrogen atoms amounts to just slightly more than 111 grams, or 0.111
kg.
Einstein's formula tells us the amount of energy this mass would be equivalent to, if it were all suddenly turned
into energy. It says that to find the energy, you multiply the mass by the square of the speed of light, this
number being 300,000,000 meters per second (a very large number):
= 0.111 x 300,000,000 x 300,000,000
= 10,000,000,000,000,000 Joules
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This is an incredible amount of energy! A Joule is not a large unit of
energy ... one Joule is about the energy released when you drop a
textbook to the floor. But the amount of energy in 30 grams of hydrogen atoms is equivalent to burning hundreds of thousands of gallons of gasoline!
If
you consider all the energy in the full kilogram of water, which also
contains oxygen atoms, the total energy equivalent is close to 10
million gallons of gasoline!
Can all this energy really be released? Has it ever been?
The only way for ALL this energy to be released is for the kilogram of water to be totally annhilated. This process involves the complete destruction of matter, and occurs only when that matter meets an equal amount of antimatter
... a substance composed of mass with a negative charge. Antimatter
does exist; it is observable as single subatomic particles in
radioactive decay, and has been created in the laboratory. But it is
rather short-lived (!), since it annihilates itself and an equal
quantity of ordinary matter as soon as it encounters anything. For this
reason, it has not yet been made in measurable quantities, so our
kilogram of water can't be turned into energy by mixing it with
'antiwater'. At least, not yet.
Another phenomenon peculiar to small elementary particles like protons
is that they combine. A single proton forms the nucleus of a hydrogen
atom. Two protons are found in the nucleus of a helium atom. This is how
the elements are formed ... all the way up to the heaviest naturally
occuring substance, uranium, which has 92 protons in its nucleus.
It is possible to make two free protons (Hydrogen nuclei) come together
to make the beginnings of a helium nucleus. This requires that the
protons be hurled at each other at a very high speed. This process
occurs in the sun, but can also be replicated on earth with lasers, magnets, or in the center of an atomic bomb. The process is called nuclear fusion.
What makes it interesting is that when the two protons are forced to
combine, they don't need as much of their energy (or mass). Two protons stuck together have less mass than two single separate protons!
When the protons are forced together, this extra mass is released ... as
energy! Typically this amounts to about 0.7% of the total mass,
converted to an amount of energy predictable using the formula .
Elements heavier than iron are unstable. Some of them are very unstable! This means that their nuclei, composed of many positively charged protons, which want to repel from each other, are liable to fall apart at any moment! We call atoms like this radioactive.
Uranium, for example, is radioactive. Every second, many of the atoms in
a chunk of uranium are falling apart. When this happens, the pieces,
which are now new elements (with fewer protons) are LESS massive in
total than the original uranium atoms. The extra mass disappears as
energy ... again according to the formula ! This process is called nuclear fission.
Both these nuclear reactions release a small portion of the mass
involved as energy. Large amounts of energy! You are probably more
familiar with their uses. Nuclear fusion is what powers a modern nuclear warhead. Nuclear fission (less powerful) is what happens in an atomic bomb (like the ones used against Japan in WWII), or in a nuclear power plant.
Albert Einstein was able to see where an understanding of this formula
would lead. Although peaceful by nature and politics, he helped write a
letter to the President of the United States, urging him to fund
research into the development of an atomic bomb ... before the
Nazis or Japan developed their own first. The result was the Manhatten
Project, which did in fact produce the first tangible evidence of ... the atomic bomb!
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