Scientists throughout the 20th century have
always worked to great lengths in order to conceptually understand the tenets
of quantum mechanics. One of these great principles of quantum mechanics is the fact that light (or any other quantum object) can only interact with matter
as either a particle or wave - never both at the same time. It is either one
form or the other. The reason behind this is because of the fundamental nature
of observing the quantum phenomena. For example, if an electron gun fires electrons
at slits that have lengths smaller than the wavelength of the electron itself,
then an interference pattern would emerge. If we ever try to observe the
electron before it hits the slits, then we would need to use light to observe
it (just like anything else). The problem is, as soon as we add light to the
electrons, they will gain energy because of the photons (light particle)
scattering off of the electrons! This will destroy the system and provide no
meaningful results. Recently, a science team at EPFL (École Polytechnique Fédérale de Lausanne) came up with
an interesting experiment that resulted in the first image of light behaving as a particle
and a wave simultaneously! The trick was to think about the imaging process:
instead of using light to image electrons, use electrons to image light. The
way they did this was by setting up a laser that fired a pulse of light at a
nanowire; this resulted in a standing wave radiating around the wire. Then the
researchers shot electrons near the wire, forcing the electrons to scatter off
the photons. Using the ultrafast microscope, they were able to image the
interactions between the photons and the electrons! The bumps in the image are
the accelerations of the electrons (changes in speed because of the collisions) at each part of the standing wave set up in
the nanowire. This basically means that the standing waveform of light in the
nanowire was successfully visualized by just using electrons! And don’t worry,
these results do not invalidate any principles of quantum mechanics; in fact
they reinforce them. In the image, we can see the standing waveform of the
light, and we can simultaneously see the interactions. This proves that the
electrons are physically interacting with the particles of light – the photons.
Voila, light is both a particle and a wave!
Hey Andrew!
ReplyDeleteI remember doing the light interference/diffusion/refraction lab in high school physics and I thought your post was really interesting! Obviously the quantum theory is the prevailing model that we use today for light, but it based on a series of independent work that either showed how light behaved as a particle, or as a wave (never both at the same time like you said before), so it's incredible how modern technology has finally allowed us to observe light behaving as both at the same time.
Your blog is really interesting and looks gorgeous - I don't really know much about physics or space but your posts are informative and engaging, and hopefully I'll learn something from reading it. Great job!