24
Dark Universe
That there could be something that we cannot see and yet affects our universe
in a profound way is a revolutionary concept. Physics for centuries had been
based on experiments that are done on things that we see, either directly or
indirectly. In the beginning of twentieth century, something drastic happened
where we could not see the objects we were dealing with, i.e. electrons and
protons, and started using them to build the laws of physics. We did not see
them, but we did see their effect indirectly in many different ways, and are
sure that they are there affecting life. When particle detectors such as cloud
chambers and bubble chambers were invented, we could see these particles
moving through them and leaving a track. We could tell whether they have
positive or negative charge using magnetic fields. Similarly, quarks, which
cannot exist as free particles, have also been indirectly seen via the tracks, called
jets. Thus seeing has, in some sense, been believing in physics.
The topic of this chapter is however not the electrons or protons or quarks
but rather a new kind of matter that we genuinely do not see and yet we know
exist. That matter is called “dark matter.” So how do we then know this exists?
This is more like a professional detective story, where circumstantial evidence
builds up to such an extent that the guilt of the suspect becomes obvious
without a shred of doubt.
The main tool that led scientists to first suspect this is through gravitational
force, which affects everything. This allows us to detect matter whether it
reflects light or not. The first person to suspect this was an astronomer in
the early part of the twentieth century, named Fritz Zwicky. Zwicky was a
Swiss astronomer born in Bulgaria who migrated to the USA in 1925 to work
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_24
179
Dark Universe
That there could be something that we cannot see and yet affects our universe
in a profound way is a revolutionary concept. Physics for centuries had been
based on experiments that are done on things that we see, either directly or
indirectly. In the beginning of twentieth century, something drastic happened
where we could not see the objects we were dealing with, i.e. electrons and
protons, and started using them to build the laws of physics. We did not see
them, but we did see their effect indirectly in many different ways, and are
sure that they are there affecting life. When particle detectors such as cloud
chambers and bubble chambers were invented, we could see these particles
moving through them and leaving a track. We could tell whether they have
positive or negative charge using magnetic fields. Similarly, quarks, which
cannot exist as free particles, have also been indirectly seen via the tracks, called
jets. Thus seeing has, in some sense, been believing in physics.
The topic of this chapter is however not the electrons or protons or quarks
but rather a new kind of matter that we genuinely do not see and yet we know
exist. That matter is called “dark matter.” So how do we then know this exists?
This is more like a professional detective story, where circumstantial evidence
builds up to such an extent that the guilt of the suspect becomes obvious
without a shred of doubt.
The main tool that led scientists to first suspect this is through gravitational
force, which affects everything. This allows us to detect matter whether it
reflects light or not. The first person to suspect this was an astronomer in
the early part of the twentieth century, named Fritz Zwicky. Zwicky was a
Swiss astronomer born in Bulgaria who migrated to the USA in 1925 to work
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer
Nature Switzerland AG 2021
R. N. Mohapatra, The Neutrino Story: One Tiny Particle’s Grand Role in the Cosmos,
https://doi.org/10.1007/978-3-030-51846-2_24
179