In a recent video I made about the search for proton decay, some commenters asked
both why scientists thought proton decay could happen and why researchers want to keep looking
when they did not find proton decay in the last attempt. This brings up a much bigger question,
which is just why is it that scientists are always looking for better equipment and experiments.
The story is actually much more complicated than that and is an excellent topic for today’s video.
(intro music)
Humanity has always been
interested in what we might call big questions, like the ones about how the cosmos began,
or why the universe is the way it is.
Indeed, some of the very earliest writings asked this same question.
This cuneiform tablet, which is dated from about 3,500 years ago, is called the Eridu Genesis,
and it details thoughts of the time about how the world and humanity came into existence.
While the tablet is over 3,000 years old, archaeologists believe the stories are much
older than that.
Thus these questions are ancient ones and while we have uncovered many answers,
there are still things that are unknown. I’ll talk about them in a minute,
as well as the need for improved equipment to obtain better data and find better answers.
Now, it’s true that some people aren’t
as interested in the big questions as I am – the questions of life and death and the nature of
reality. While they may not get the same thrill I do about uncovering a deeper and more fundamental
layer of nature or getting closer to understanding the underlying nature of the entire cosmos,
they still benefit from the science.
For example, back in the 1700s, electricity wasn’t understood all that well. It mostly was a topic
for eccentric guys to putter with in their labs and a parlor trick used to amaze rich people at
parties. And now it powers our entire society.
While I personally don’t understand it, particle physics isn’t everyone’s cup of tea; however,
we’ve all benefited greatly from the field. For example, researchers at CERN, the European
equivalent of Fermilab, invented the World Wide Web some 30 years ago. It revolutionized the
world, speeding up commerce and communication, and giving everyone with a cell phone or computer
access to unprecedented information.
However, for me and people like the ones who wrote the Eridu Genesis tablet over three millennia ago,
these spinoffs are just nice side effects – something to make our lives easier. They don’t
get to the key point, which is to answer ancient questions about the universe and why we’re here.
So, fast forward until the modern day.
We now know a great deal about the fundamental natures of matter and energy, space and time.
Rather than the medieval notion of the planets moving by the beating of angels’ wings,
we now understand gravity and how it works. This knowledge has allowed us to explore the solar
system and study the workings of galaxies and black holes. The theory that best describes the
cosmos is called the General Theory of Relativity.
On the microscopic side, while the ancient Greeks pondered whether fire, water, earth,
and air were the crucial elements, we now know of the atomic model of matter. And, here at Fermilab
and at other similar facilities, we have dug even deeper, learning what exists inside atoms. We
know of nuclear fusion which powers the sun. We know how to transmute energy into matter
and vice versa. We know of a substance called antimatter, which sounds like science fiction,
but is definitely real. The name of the theory that best describes the subatomic realm is the
Standard Model of particle physics.
Together, general relativity and the standard model showcase our very best understanding of
the laws of nature. We have made great strides towards shedding light on the questions first
written down on the Eridu Genesis tablet.
However, despite our successes, we aren’t done.
There remain unanswered questions and I want to share half a dozen or so of them. And,
by the way, I have made videos going into all of them in more depth. The links are in the
description below.
My first example: Why do galaxies rotate much faster than the known laws of physics allow?
One possible explanation is that there exists a form of matter, called dark matter,
that exerts a gravitational force but neither emits, nor absorbs, light.
Whether dark matter may or may not exist, finding the answer to the question of the speedily
spinning galaxies remains. Scientists around the world are seeking to find the answer using
various experimental approaches and comparing theoretical predications to measurements.
Here’s another example: The universe is expanding,
which the theory of the Big Bang explains. However, the expansion is accelerating, requiring
that there be a form of repulsive gravity. The proposed solution for this is called dark energy,
however, we don’t really understand dark energy, except to think it’s a property of space.
The full explanation eludes us, and a detailed understanding of the accelerating expansion of
the universe remains an open question.
We also know that there are interesting regularities in the pattern of quarks and
leptons. While it just might be a coincidence, the pattern looks a bit like the chemical periodic
table of elements. The explanation for the periodic table was that atoms were made of smaller
things, arranged in complex ways, with a nucleus and an electron cloud. The patterns in quarks and
leptons may or may not have the same answer, but whether or not that is true, we still don’t know
the answer of why the pattern persists.
My fourth example involves understanding the nature of the origins of the universe,
which relies on two seemingly contradictory things. One is that the universe began in a
hot dense state called the Big Bang and the early universe was full of energy.
The second thing is that energy can be converted into matter and antimatter. Both of these things
have been validated. Yet, when we combine these two ideas, we find that we can’t explain our
universe. Our universe is made solely of matter, while the theories say that we should have equal
amounts of matter and antimatter. That’s another unanswered question…in fact, it’s one of the
driving reasons why the Fermilab research program is upgrading our particle accelerator complex and
developing huge new particle detectors.
The discovery of the Higgs boson was the culmination of half a century of
work. The Higgs boson was predicted in 1964 and discovered in 2012.
The boson gives mass to subatomic particles. It was predicted and we found it. However,
there is a problem. The standard model predicts that the mass of the Higgs boson should be
ginormous, but it’s not. While we have some ideas as to why the prediction could be flawed, we have
a fifth unanswered question. This is a technical point, but it shows that as successful as the
standard model is, its answers are incomplete.
The sixth question has to do with a historical trend. Isaac Newton realized that the gravity
on the Earth and in the heavens are one and the same. James Clerk Maxwell proved
that electricity and magnetism are the same. And, with the discovery of the Higgs boson,
researchers proved that electromagnetism and the weak nuclear force are the same.
It remains quite possible that in the future, we’ll discover additional cases of seemingly
different forces actually having a single cause. Maybe at the base of it all, there is only one
force. It’s another question that, if we answer it, will teach us something fundamental about the
laws of nature.
I listed half a dozen questions, but there are more. While the standard model and general
relativity are amazing accomplishments, they aren’t complete. They leave questions that we
need to answer to get to the bottom of things.
So, that brings us to the related question, which is “how do we answer these science questions?”
And the answer is simple. We have smart people think up ideas and we have other smart people
think about ways to build equipment that can both test those ideas and generate data that will point
researchers in the right direction.
The problem, of course, is that nobody knows the answer. So, what we have to do is tackle
the questions in different ways and come up with many smart ideas. We test those ideas against
existing data and throw out the ones that disagree with past and current measurements. What is left
are theories that agree with everything we know and potentially answer unanswered questions.
How does this work in practice? Well,
as an example, let me return to my video on proton decay. Back in the 1980s, some theoretical
physicists came up with some ideas that might explain how the various forces might unify.
The mathematical ideas were complex, involving a lot of geometry, but one consequence of the ideas
was that protons would decay. So giant detectors were built to study the stability of protons.
The result was that no proton decay was observed. But the detectors did observe
solar neutrinos and neutrino oscillations, and Nobel Prizes were awarded for these discoveries.
Moving forward, researchers wouldn’t build a detector just to look for proton decay. However,
if detectors were built for other reasons that were big enough, it would be irresponsible to
not also use them to look for proton decay and other elusive subatomic phenomena.
That’s the case with Fermilab’s Deep Underground Neutrino Experiment and Japan’s Hyper Kamiokande.
They’re both being built to do neutrino studies, and the proton decay studies come more or less
for free.
On the dark matter front, there have been dozens of experiments looking for lots of
different kinds of dark matter and none of them have found it. While it could
be true that this means that dark matter doesn’t exist, it is still true that the question of why
galaxies rotate so quickly remains unanswered. Because of that, scientists continue to come up
with ideas – some of which involve dark matter and some of which explore other explanations.
Whatever the explanation, we’ll only be able to resolve the question using experiments and data.
Then there are
particle accelerators. Since their invention around 100 years ago, particle accelerators
have been an incredible source of data for physics research. Indeed, without particle accelerators,
the standard model would have never been devised. We would never have known about quarks. We would
have never understood the Higgs boson and how particles get mass. We’d be stuck back at the
understanding of a century ago.
Fermilab’s Tevatron was the world’s most powerful accelerator from the mid 1980s until 2009.
During that time, Fermilab researchers discovered the tau neutrino and the top quark,
made important measurements that might help us understand why there is no antimatter
in the universe, and made many other advances in understanding the subatomic
world.
Currently, the Large Hadron Collider is the most powerful accelerator. Using it, we discovered the
Higgs boson, and we are exploring in more and more detail how the Higgs boson interacts with other
bosons and quarks. We’ve also found many particles made of quarks that had never been seen before.
Combining all of the measurements done using the accelerator, we’ve published more than
3,000 scientific papers to share the data and knowledge we’ve gained.
Despite these discoveries, we still have many
unanswered questions, and even the next generation of experiments are unlikely to answer them all.
Based on the century-long success we’ve had with building more and more powerful accelerators, it's
very reasonable to think that finding more answers requires a more powerful particle accelerator.
Of course, it’s important that when one builds such an accelerator and associated detectors that
they be multi-purpose machines that can answer many questions. Basically, that way you get more
bang for your buck.
I think a key point is that it’s important to remember that the equipment isn’t what’s
driving this. What’s driving the inquiry are the questions – the unanswered conundrums that keep us
awake at night. To answer questions, sometimes bigger is better. On the other hand, sometimes
a small experiment is what fits the bill. And it takes careful thought to decide what’s best.
In order to recommend which
proposed experiments are the most promising ones, the particle physics community gets together every
five or ten years to take stock and decide which approaches are most likely to generate results.
The European scientific community just finished such a review, while the American evaluation is
going on right now. For several years, using what is called the Snowmass process, researchers have
examined many ideas to make a case for this future project or that. And now, a group called the
Particle Physics Projects Prioritization Panel, or P5, is evaluating all those ideas. P5 will then
do its best to emphasize the promising ideas and reject the ones that seem less likely to help.
Finally, P5 will make their findings available to funding agencies, which will make the final
determination on which projects to pursue and which ones not. It’s a process designed to select
the most promising future research.
But, as you think about what scientists are doing, it’s important to go full circle and
remember why we’re doing this at all. Just as the first writings wrestle with questions like
the origins of the universe and the deepest laws of nature, scientists today do the same thing.
We’ve made incredible progress over the past few centuries, but the journey continues.
The final answer eludes us and it’s going to take a lot of hard work and clever experiments
to get us to the end of the road. This isn’t a project that will be solved in
months or years – it will take lifetimes. It’s important to remember an inescapable
truth - the only way to complete a journey is to keep taking steps. And that’s what we’re doing.
(phasing sound)
Okay- that
was maybe a deep video. Every so often, it’s important to take a step back and see the big
picture. This neat problem may be interesting, or that one may teach us something, but at some
level those are all details. The final answer is much bigger than any question. On the other hand,
progress depends crucially on answering questions and answering questions depends
on having the right equipment and experiments to do that. Only by this hard work will we
maybe finally shed light on the biggest questions ever tackled by humanity – well, physics ones at
least. And that will be a great day because, as I have often said, physics is everything.
(outro music)