Turning Points in Physics

Discovery of the electron

During the 1880s and 90s, scientists searched cathode rays for the carrier of charge in matter. Their efforts resulted in the discovery of the electron by J. J. Thomson in 1897. Thomson directed the cathode rays through two parallel metal plates to the glass end of a tube. The rays went down when the upper aluminium plate was negative and up when it was positive. The deflection reflected the potential difference between the plates. Cathode rays were clearly negatively charged particles based on magnetic and electric deflections. Thomson discovered the granularity of electricity, which explains how individual particles carry a charge.

• The idea of a homogenous atom particle was disproved.

• The existence of subatomic particles was proved.

• Dalton’s atomic theory assumption that atoms were indivisible was disproved.

Wave-particle duality

Wave-particle duality was born from the work of many scientists such as Max Planck, Albert Einstein, Louis de Broglie, Erwin Schrödinger, Niels Bohr, and Arthur Compton. In quantum physics, wave-particle duality states that each particle or quantum phenomenon may be represented as a particle or a wave. This theory gave rise to major discoveries, such as:

• A differential equation that describes how a wave function can explain all aspects of the behaviour of light and matter.
• The recognition that light and matter have characteristics that are both wave-like and particle-like.

Special relativity

In 1905, Albert Einstein developed the theory of special relativity. However, the idea of relativity did not begin with him, as Galileo and Newton had been exploring relativity for centuries. The concept of relativity expresses the realisation that the laws of physics depend on the observer.

For example, if you fly into space at nearly the speed of light, time runs more slowly on your spacecraft than it does on the earth. So when you return to the earth, you will find that your friends have grown older than you have.

It is possible to divide modern relativity into two theories, special relativity and general relativity. The theory of special relativity is important because:

• It states that the laws of physics are the same and can be stated in their simplest form in all inertial frames of reference.
• It states that the speed of light (c ) is constant and independent of the relative motion of the source.
• An outcome of this theory is the famous equation: E = mc².

Einstein is well-known because his theories of relativity made ground-breaking predictions that came to fruition in the real world. Most significantly, his hypotheses have been proven to have been highly precise in a wide range of experiments, forever transforming our understanding of space and time.

Albert Einstein

How did turning points in physics influence science?

Turning points in physics have provided fundamental knowledge that has led to further discoveries and influenced technology in many ways. Examples include:

• The discovery of the electron, which brought in a new era in physical science, thus paving the way for modern ideas of atomic structure and chemistry.

• Wave-particle duality, which highlighted the inability of classical terms such as ‘particle’ and ‘wave’ to explain quantum-scale object behaviour.

• Special relativity theory, which has had a significant influence on physics, particularly in the computation and comprehension of high-velocity events. As a result, we now have a far better grasp of space and time than we did at the start of the century.