What it means to be a theoretical astrophysicist

Humanity’s passion for discovery has been exemplified by scientists and philosophers like Galileo and Einstein. But how have their scientific ideas shaped our understanding of the cosmos today? Theoretical physicist and Yale University professor, Priyamvada Natarajan, joins Hari Sreenivasan to discuss the scientific theories and how they gain acceptance.


Humanity's passion for discovery has been exemplified by scientists and philosophers, like Galileo and Einstein, but how have their scientific ideas shaped our understanding of the cosmos today?

Joining me now to discuss the scientific theories and how they gain acceptance is theoretical astrophysicist and Yale University professor Priya Natarajan.

So, theoretical astrophysicist is always one of those like, 'What does that mean?

What do they do?

They theorize about what?'

How do these ideas become accepted by the general public?

I think the first hurdle is that when scientists propose radical ideas -- For example, now that we have an inventory of our universe, we know that the primary constituents are these very peculiar things.

They are dark matter and dark energy, both of which are invisible elements.

And, so, the scientific community itself grapples and has a lot of difficulty dealing with the new proposals.

So, the idea of dark matter was inferred by looking at the gravitational effect that dark matter, although it's invisible, exerts on the motions of stars and galaxies.

So it's everywhere.

It's smeared everywhere, but it's clumped in certain places in the cosmos.

And, so, it's those regions where it's clumped that we have a really good handle on mapping it.

So, one of the properties that we explored is from Einstein's Theory of General Relativity, which is the presence of mass, whether it emits radiation or not, just mass, would deflect light rays.

So, the presence of a huge concentration of dark matter would deflect light rays -- that is, the light from galaxies behind this clump.

So it would kind of go around it.

It'll go around it and it will give us a distorted view of what those galaxies actually look like.

And because there are patches in the universe where dark matter is not so clumped, we know what it should look like when there's not so much distortion.

So, given that we know what a 'normal' patch should look like, we can infer what this distorted patch means for the amount of dark matter that is distributed.

You know, for a non-scientist who's like, 'Look, I can't see it, I can't believe it,' but a group of you-all who are debating in academic journals about whether this distortion should exist or not, why is it hard for scientists to embrace the possibility of something radical?

Well, I think that there's a history in particular -- right? -- of all these 'unseen quantities' going away.

So, there was this idea of miasma, which is this invisible fluid that causes diseases, before we had the pathogen idea for diseases, or ether -- that was a medium that was needed for light.

So, all of these invisible elements actually vanished.

They were shown to be nonexistent.

So, I think there's the first resistance is that.

At the end of the day -- right? -- we're human beings, and our psychology is such that we are a little averse to change.


So, for example, you know, Einstein is key example.

He came up with the most radical ideas, right?

He transformed our understanding of gravity and space-time and black holes and all of that.

But he resisted the implications when he understood the physics.

So, he was so wedded to the idea of a static universe that when his equations implied that the universe should be expanding and there was incontrovertible observational evidence, he was a holdout.

It took him a long time.

And, finally, he said, in 1929, after discovered the expansion, sort of that galaxies that were farther away from us were hurtling away faster, Einstein famously stood up at a seminar, in 1929, and said, 'Okay, I was wrong.

The universe is expanding.'

However, some colleagues of mine recently discovered an unpublished manuscript, which was incorrect, so Einstein actually didn't end up submitting it, dated 1931, where he was still trying to recover the idea of a static universe.

So, you know, publicly, he accepted it, but, emotionally, he struggled with the idea.

The comfort that a static universe gave -- right? -- was something that was hard for him to get over.

Similarly with the idea of a black hole.

The fact that the black hole is this peculiar object that encases a singularity, a place where all known laws of physics break down, he just thought, 'This is not natural.

Nature would not permit such a perverse object.'

And it took him a long time to actually accept that, you know, black holes became real.

And, of course, they became really real with the LIGO detection right now.

You know, we're literally talking about a genius and his resistance to what was a series of facts.

What about the general American population or just the population on Earth?

When we talk incontrovertible scientific evidence, we're very, very doubtful.

Right. And I think that's one of the goals of my new book, 'Mapping the Heavens,' where I've been really puzzled and fascinated at why Americans are so resistant to new scientific ideas and scientific ideas and science in general.

So the general disbelief in science.

So, one thing that I wanted to do with my book was to show how, in the process of science, everything is really provisional.

So our current state of knowledge is the best to date what we know and that when we have more data -- So, it's the interplay of ideas and instruments.

When we have better data, more data, then, you know, our picture, our theoretical picture, can either get honed and refined or, very occasionally, the theory can get completely overthrown, right?

By in large, we have reached a level of sophistication in our understanding that things really do get just honed a little bit.

And I think the public has a lot of difficulty comprehending the fact that things can change.

But these changes are not hugely disruptive.


They are part of refining our understanding and getting a deeper understanding.

It's part of the training that we have to be open-minded.

And part of what I wanted to show is that despite our training, a lot of us struggle when we face -- So, it's just, you know, the psychological part of us which is resistant to change.

In the last few years, we've had these major moments, at least scientifically, of the gravitational waves or the Higgs boson, or the 'God Particle.'

I mean, these are big, massive leaps, and the scientific community's still kind of adjusting to that.

'Okay, I guess that really happened?

That really did happen?

Okay. What does that mean for all my research and everything that I've been pursuing for 20 years.

So, I think we are a little bit ahead in terms of acceptance, and the public soon follows.

And I think the scientists have now realized that we actually have a responsibility to the public to explain what is going on.

These are momentous discoveries.

And it's often said -- It's a cliché. It's said that 'we're in the golden age of cosmology.'

We actually are.

And the reason for that is that both the ideas, our theoretical ideas, and technology and instruments have reached a sophistication that now matches.

It used to be that you could theorize about all kinds of things, you know, many, many possibilities, and they were not all testable right away.

It would take 50 years to test something.

Now you can make a prediction, and within 5 to 10 years, it's testable.

The match in sophistication is really what's making it a golden age, but with technology moving at the pace that it is, I think we may soon be at a time when technology is going to outpace our ability to generate new ideas and that new ideas will, therefore, have to be generated in a different way.

I think that's already starting to happen in fields like astronomy.

It used to be that, you know, there were individual, lone geniuses, right?

And now the work is done in big scientific teams.

So it's sort of distributed intelligence and expertise.

You need the expertise of many different people to sort of combine and synergize to come up with a new idea or to test it.

Priya Natarajan, from Yale University, thanks for joining us.

Thank you so much.