Gravitational lensing, Refraction & Diffraction: Three sides to the same coin?
difference between the terms and their affects on light, both from wave and particle point of view).
Since space is curved, light doesn’t travel through space in
a ‘straight’ line (at least, not a straight line as you traditionally envision a straight line). Einstein’s theory of general relativity predicts that light
should be bent by the gravitational fields of bodies with mass in the Universe. In his theory, the light that comes off points near the sun would be bent
slightly inward because of the Sun’s mass. So, if the light traveling from a distant star passed close to the sun, it would be deflected by a small angle,
which would cause the star to appear in a different position relative to our vantage point on Earth. Of course, if the light of any distant star always had to
travel close to the sun relative to our point of view, we wouldn’t be able to tell the light was being deflected. We would probably assume the star was really
located where it appears to be.
The sun emits quite a bit of visible light, so seeing the changes in a stars position
when its light is obstructed by the sun, relative to other stars — is difficult. However, this can be monitored. As the Earth and other planets in our solar
system orbit around the sun, distant stars will appear to pass behind the sun and have their light deflected. Not only can this phenomenon be verified during
total lunar eclipses, but it’s also a prediction made by Einstein’s theory of general relativity. So, what useful purposes does it serve otherwise? It’s
actually a good tool for observing distant objects in space that would be difficult to see otherwise using even the most powerful of telescopes on Earth.
Reflection – Refraction – Diffraction:
Thanks to Young’s infamous double slit
experiment (which I’ve written about before, you can find the article in the sources at the bottom of this article), we know that light exhibits certain
behaviors of both a wave and particle. This must be understood in order to fully grasp the concepts of both refraction and diffraction, since both are related
in the aspect that they both deal with the bending of waves.
First, diffraction: You may have heard that our night sky
isn’t particularly honest. Be it light pollution or diffraction, it isn’t a true representation of what space actually looks like when compared to
observations made in outer space. If you inserted a straw into a glass of water, and angled the glass right, the straw appears broken from your perspective…
even though it’s fully intact. This is because light is diffracted in our atmosphere and in a glass of liquid. This basically means that light tends to bend
around particles or other obstacles and spreads apart, erupting into regions that may otherwise be shadowed.
Refraction, when a wave is traveling at any angle that isn’t at exactly 90 degrees, its line of travel will change when it passes the boundary between one
medium to another. Its path will then refract, or become “bent,” but the direction of the bending of the wave is highly dependent on the relative speed of the
two. As an example, a wave will bend in the opposite direction from the direction it started in if it’s moving from a fast medium to a slow medium. Light
isn’t the only wave that experiences refraction. Both water and sound waves do the same.
As for diffraction, light will
change directions as it approaches an opening before passing through from one medium to another, so will waves.
Here’s a summary of the difference between diffraction and refraction
– Diffraction is bending or spreading of waves
around an obstacle, while refraction is bending of waves due to change of speed.
– Both diffraction and refraction are
wavelength dependent. Hence, both can split white light in to its component wavelengths.
– Diffraction of light produces
a fringe pattern, whereas refraction creates visual illusions but not fringe patterns.
– Refraction can make objects
appear closer than they really are, but diffraction can not do that.
FQTQ Related Reading:
Sources and further reading:
Difference between diffraction and refraction:
How do we know light
behaves as a wave: