Tirthabir Biswas: Research Home Page

My principle research areas are cosmology and gravitational physics. Over the years, I have had the opportunity to work at several excellent physicists who are scattered all over the globe. One of my goals is to also involve undergraduates in my research. Please visit our Cosmology Group page for more information on the kind of collaborative research projects my students are involved in. Also, here is a list of my current research projects and future opportunities for students to participate in. Below I briefly discuss some of my motivations and broad research themes.

The Fundamental Forces of Nature

As far as we know the universe is ruled by four different forces:(i) Electromagnetic (ii) weak nuclear (iii) strong nuclear and (iv) gravitational. We seem to have reached a rather sophisticated level of understanding of the inner working of the first three, their study being commonly referred to as Particle Physics. For instance, Salam and Weinberg independently demonstrated how the first two forces can be unified into a single "electro-weak" theory. While the strong force has not genuinely been unified with the other two, the fundamental physical principles behind all the three forces are essentially the same. So, all these theories can be "quantized" in a very similar manner to provide us with predictions on how the fundamental particles interact with one another, and have been extremely successful experimentally. Last year, the final piece of the puzzle, namely the existence of the "Higgs boson", has been all but confirmed in the multi-billion dollar Large Hadron Collider experiment. 

In contrast, gravity has been an enigma. While Einstein's General theory of Relativity (GR) has been incredibly successful in passing astronomical, cosmological and lab based experiments, it is plagued with infinities. In cosmology this shows up as the Big Bang singularity, our universe seem to have been born from a single spatial point of infinite density at a finite time in the past. How and why did time began? Astronomers have now discovered that at the center of most massive galaxies there exist a gigantic "super-massive" black hole. Unfortunately, in GR the space time describing a black hole seems to run into a singularity where space becomes "inifinitely curved". Finally, any attempt to quantize the theory to predict interactions of gravitational excitations/particles, also known as gravitons, seem to run into mathematical infinities which we are yet to master.  The essential problem with understanding gravity is that it is too weak to study comprehensively in our labs. To illustrate the contrast with particle physics, we have to ramp up the energy scale (energy per particle undergoing collisions) by a factor of 1000,000,000,000,00 from what is on display at LHC  to capture some of the strong gravitational effects we want to understand.

Cosmology

This is one of the reasons why cosmology is interesting. Our universe is believed to once have been so hot, or equivalently particle energies so high, that we may be able to probe strong gravitational physics. Cosmology is also a door way to finding new particles and interactions that can only be excited at such high energies. For instance, Grand Unified theories  of particle physics which attempt to unify the electro-weak force with strong nuclear force predict new particles and new forces at such energies. Can their presence in the early universe been somehow imprinted in the universe that we observe today?

Finally, the story of our universe is itself fascinating and full of surprises. Did our universe emerge from a singularity? Was there a beginning of time, or can one trace time all the way back to eternity? What about dark matter and dark energy, why do we need them, and how do we find what they are? My research tries to address these questions. In particular, I am interested to find cosmological paradigms that predicts distinct signatures from physics of strong gravity and/or new particle physics interactions.