Adam Riess: The Star Gazer

It was a casual conversation with his dad as a young child that first started Adam Riess on his path

• "Wrapping my head around this image of a star not being there but the light traveling, it just gets into those juicy issues about physics and the really fascinating aspects of it" - Adam Riess

• His big catalyst was a summer program in his home state of New Jersey (Governor's School of Science).

• He was one of 100 students selected to take advanced courses at a local university.
• It was there that he was first exposed to the "mind-blowing" ideas of general and special relativity.

• He then went on to graduate from MIT and completed his Ph.D. at Harvard.

• After his Ph.D. he worked his way from Berkeley as a postdoc to the Space Telescope Science Institute at Johns Hopkins.

• Adam attributes his success to three things:

• His mentor and Ph.D. advisor Bob Kirshner
• Great colleagues and team members
• A strong sense of curiosity and a dogged pursuit of puzzles

• "Man’s character is revealed when no one is looking" - Adam Riess

• Adam avoided the Academic Hunger Games: Get into a great school, write a good thesis, get a good postdoc, faculty and so on. Has that system broken?
• It’s not a great scheme.
• Adam was not compelled by that scheme. He decided early NOT to checkboxes on a path, and instead, do what he found fun and engaging.
• If you’re checking boxes, you’re in the wrong field.
• It might look like you’re working hard, but if it’s fun you won’t feel like you’ve worked a day in your life.

• Adam's work in optical astronomy at Johns Hopkins was about addressing some of the most interesting questions in cosmology:

• How old is the universe?
• What is the fate of the universe?

• His work involved improving the ability to measure the rate of the universe's expansion by pushing those measurements further back in time.
• The further back in time the measurements can go, the better we can understand both the trajectory and the rate at which the universe expands.
• "We thought it would be slowing down. Instead, we found, to our great surprise, it was speeding up!" - Adam Riess

How did Adam deal with fears of missing out, not being cited or credited, or imposter syndrome?
NOTE: HOW NOBEL WINNERS DEAL WITH THE IMPOSTER SYNDROME IS A MAJOR THEME OF THIS BOOK

• He understood early on that most individuals in science only focus on a niche within their domain.
• But being nominated for and winning the Nobel Prize was less about genius and more about expertise and luck:
• "I quickly realized it's not an IQ test, it's not a ranking of great physicists. It's for people who for the most part were lucky that they were in the right place at the right time and contributed to a discovery." - Adam Riess

Cosmology dares to address really big questions like, “How did this all start and where is it all going?” Hawking quote on God from Brief History here...take away choice with TOE.

• It isn't interested in answering questions like why there is a universe or how one should act in it.
• These questions are still in the realm of philosophy and religion.
• Science is only concerned with the kinematics of the universe and what can be measured.
• This includes things like motion, distance, temperature, etc.
• "Cosmology draws us to the possibility of addressing those really big questions which is where a lot of controversy can be as well" - Adam Riess

The standard model of cosmology is a kind of story, or biography, of the universe that stretches back to the Big Bang and helps us understand the current composition of the universe.

• The Big Bang Model

• The universe began approximately 13 billion years ago.
• It began by expanding from an inconceivably hot, dense state.
• Since then, the universe has continued expanding and cooling resulting in the universe we know today.
• In the first 10^-34 seconds or so of the universe's history, it underwent a brief period of extremely fast expansion, known as inflation.
• Not long after, matter began to arise from a poorly-understood process called baryogenesis.
• Protons, neutrons, and electrons are examples of baryons.
• After about 100,000 years, the universe cooled enough to allow for the formation of atoms.
• This process occurred during a period called the era of recombination .
• After the formation of atoms, light could travel large distances without running into anything that might knock it off course.
• The light released at this time is perceived today as the cosmic microwave background (CMB) , or the afterglow of the heat of the Big Bang.
• A few hundred million years after this period, galaxies and stars began to form.

Baryonic Matter: ~5%

• "Normal matter" like stars, planets, people, etc.

Cold Dark Matter: ~25%

• The "missing mass" of the universe.

Dark Energy: ~70%

• The proposed energy powering the expansion of the universe.

• Neither dark energy or dark matter are currently well understood.

What is the 9% difference and why does it matter?

• Adam and his team have made the most precise measurement of the universe's expansion yet.

• But their value is 9% larger than what’s currently predicted by our current models of the universe and what has been previously measured.

• This 9% difference is also known as the "Hubble tension" because the Hubble constant  (H₀ ) is the unit of measurement used to describe the expansion of the universe.

• "What we're finding... is whenever we measure how fast the universe is expanding today with different methods we always get a higher number, and quite significantly so, than this very precise measurement at early times coupled with the prediction based on our understanding of the universe." - Adam Riess

• In addition, this discrepancy resides in a model where 95% of the universe is in the form of dark matter and dark energy; these are concepts not currently well understood by cosmologists.

• "Cosmologists are very good at giving names and making it sound like we know what's going on." - Adam Riess

• Adam likens this result to measuring the height of a child as it grows during infancy and extrapolating its height into adulthood only to discover that your prediction was off by two feet!
• But because we only have one universe and nothing to compare results to, researchers have no way to gauge what is "normal" and what isn't.

• There is some contention within the cosmology community about whether there is a Hubble tension at all.

• A group at Oxford led by Subir Sarkar posits that dark energy might not even exist.

• Their contention about the existence of dark energy in part arises from the fact that the naïve expectation for dark energy, or the cosmological constant, is off by roughly 120 orders of magnitude.
• This is known as the cosmological constant paradox.

• The paradox derives from the fact that when one calculates the vacuum energy density  of the universe based on known principles of quantum mechanics, one obtains the incredible result that empty space "weighs" 10⁹³  grams per cubic centimeter.
• But the measured average mass density of the universe is 10^-28  grams per cubic centimeter, meaning the predicted value of the cosmological constant is roughly 120 orders of magnitude greater than the measured value.

• "[This discrepancy] gives infinite rope to people who are going to express doubts, particularly about the data, and say, 'I'm just going to cherry-pick this piece of the data and I'm going to do this kind of funky analysis that one normally doesn't do but I can do in this situation.'" - Adam Riess

• But Adam is a big believer in not censoring data.

• He thinks that Subir discards too much of the data we currently have on the nature of the universe without actually resolving the tension between prediction and data.

• Adam believes that, because our predictions haven't been very successful ab initio (from the beginning) we should instead let the data we observe and collect guide us.

• Interjected with the important point that there exists "the notion that scientists are somehow immune from the very biases that make human beings human beings, such as confirmation bias."

• This is, of course, false.
• Bias in scientists is documented as far back as Galileo, who didn't use his best examples or data to bolster the Copernican hypothesis.

• I also observed that confirmation bias might be finding its way into modern statistical research methodologies (see: Bayes Rule ).

• Einstein, however, had the magnanimity to admit that he was wrong about expansion.

• Einstein was originally operating from the premise that the universe was static and not expanding.

• His original equations of general relativity included a positive constant value to offset the attractive effects of gravity on ordinary matter to keep everything "still."
• This assumption that the universe was static stemmed from the scientific limitations of the day, such as the fact that astronomers were unable to separate the galaxy we live in, the Milky Way, from the larger universe.

• Ultimately, Einstein wasn't a victim of his own biases so much as a victim of bad data.

• He eventually abandoned his cosmological constant and embraced a model of an expanding universe.
• Most physicists of the twentieth century then assumed the cosmological constant to be zero.
• If this was true, it would mean that the expansion of the universe would be decelerating.

• In 1998, however, Adam and his team introduced the theory of an accelerating universe.
• Now, a positive cosmological constant has been revived as a simple explanation for the "dark energy" required for an accelerating universe.

• "I don’t see it as a blunder of Einstein, I've always seen it as another statement of his brilliance. To be able to, in 1916, discover the possibility that empty space can have repulsive gravity and for us, in 1998, to say, 'You know, I think he was right.'" - Adam Riess

• Why is cosmology such a difficult science?

• Data is difficult to acquire and analyze.
• Very different types of data, often collected through different observational lenses, have to corroborate and support the same conclusion.

• This is true of theorists as well, who are often thinking about the nature of the universe in different ways and trying to come to similar conclusions.

• What makes the scientific process so robust is that it focuses on reproducibility.

• Errors in data or in data collection are unlikely to be reproduced across multiple data sets.
• This means that, over time, a consensus can be reached about the reality of what is being investigated.
• "Mathematical ideas are not something that you can develop and come to from a different direction and keep arriving at the same place. It's this reproducibility that really defines what is special about science and leads us to think we're on the right track." - Adam Riess

• Inflation, acceleration, and the Hubble tension may be anomalies of some additional, currently unknown expansion (or not!).

• It's difficult to tell from the current data whether these are separate, related, or anomalous conditions.
• In addition, these detected phenomena are not easily addressed with our current understanding of gravity without invoking some kind of energy of empty space (currently, dark energy).

• This may mean that a new area of physics research is surfacing, or it might mean we need a better story, and more information, to account for them.

• "Whenever we see the universe experience periods of anomalous expansion, we're attributing it to excess vacuum energy of space. Maybe at some point we will understand how they relate to each other, some way to connect them together." - Adam Riess

• A favorite new hypothesis of mine in cosmology that might resolve the Hubble tension: primordial magnetic fields.

• This hypothesis originates from the detection of magnetized space in the expanse between galaxy clusters, some 10 million light-years wide.
• One of the current leading ideas is that these magnetic fields, if they originated at some point during the early universe, would change the way the early universe operated.

• These changes would affect some underlying quantities cosmologists measure and, by extension, change our ability to predict the Hubble constant or expansion of the universe.

• Adam is a little more bearish on the explanatory power of primordial magnetic fields.

• "I mean, there's a certain sensibility to sort of say, 'A phenomenon we don't understand - the excess Hubble expansion - and a thing we don't understand [the primordial magnetic fields], maybe they explain each other.' I mean, I don't know." - Adam Riess

• I discussed how they're currently trying to determine if these magnetic fields existed during the early universe by using information encoded in the cosmic microwave background (CMB).

• How does this work?

• We can only detect light that is on a path pointed directly at Earth.
• This light has been traveling some 13 billion years, eventually reaching telescopes on Earth without having been scattered.

• This light can then be traced back to where it originated, when it last scattered off electrons when the universe was still a hot, dense plasma.

• If the electron experienced a uniform temperature around it, then the photons generated by the plasma and scattered by the electron are unpolarized.
• If the electron experienced a non-uniform temperature around it (areas of hot and cold), then the photons generated by the plasma and scattered by the electron are polarized.

• A small portion (~10%) of the CMB is polarized.

• The patterns observed in the polarized fraction can be split into two components, called E-modes and B-modes .

• These modes carry very different and complementary information.

• Magnetic fields generate B-mode polarization in the CMB due to Faraday rotation  of the E-mode.

• "I think if you could find these magnetic fields, which are ubiquitous, I mean we have them in our bodies and we have in it our solar system and beyond... I think that would require the least modification to the laws of physics."
• You can read more about primordial magnetic fields here .

• The cosmos is littered with dust and other material remnants.

• The pervasiveness of space dust can stymie our ability to make proper observations from Earth, itself "a speck of dust floating on a sunbeam."

• This reality brings to light some of the difficulties inherent to cosmological experiments:

• "The difference between a statistical error, which can be reduced with more data, and a systematic error that's intrinsic to your system or the cosmos itself is very profound."

• Statistical (or random) errorsi usually result from an inability to take the same measurement in an identical way to get exactly the same number. The more raw data available, however, the easier these errors are to identify and reduce.
• Systematic errors, on the other hand, are reproducible inaccuracies that are consistently in the same direction. These types of errors are often due to a problem which persists throughout the entire experiment, including its design and instrumental effects.

• According to Adam, the best way to find systematic errors is to subject your work to scrutiny by your peers and really listen to their feedback.

• "But you really will do well to listen to those critics and then try and come up with an experiment or a measurement or a test. And if it succeeds, go back to them and say, “Is this convincing or not?” And then continue the process." - Adam Riess

• This process naturally depends on the size of the claim being made and what kind of support it has (or doesn't) within the scientific community.
• As Carl Sagan said, “Extraordinary claims require extraordinary evidence.”

• Has winning the Nobel Prize had any influence on Adam and his work?

• He doesn't feel it's had much effect on his work.
• But he does acknowledge living during exciting times when many of the big questions of cosmology are being answered:

• Is there enough matter to close the universe?
• What is the ultimate fate of the universe?
• What is the age of the universe?
• How fast is the universe expanding?

• "We don't know the answers to everything, but I would say we went from almost like the pre-Magellan view of the world to post-Magellan maps. I just feel lucky that we've been around during that time." - Adam Riess

• Is there anything about The Nobel Prize that Adam would change?

• Adam thinks that the size of the group that can be recognized should increase.
• The current size (3) restriction is from a time when many scientific breakthroughs could reasonably come from one to three individuals.
• "But today, as you and I both know, science is done generally in large groups or teams working together and that kind of division of labor allows us to do bigger and better, more exciting things. We build off of each other's work." - Adam Riess

• What does Adam leave in his ethical will?

• "I think the best guiding advice or light that comes directly from science, from physics, from everything I've experienced, is to be curious." - Adam Riess

• Science is about embracing this curiosity and questioning even some of the most basic assumptions about how things work:

• What is real?
• What is right?
• What is reality?
• What is rational?

• As long as scientists are willing and able to ask and seek out the answers to such questions, they'll be well served.

• If Adam had to make a billion-year time capsule, what would he include?

• "You know, there's this very compelling idea I've seen about storing all the seeds of every kind of plant that's ever lived. Consider the complexity of the process that evolution went through to realize each of those. I might put a kind of Noah's Ark of the plant world into my monolith." - Adam Riess

• What would Adam tell his 20-year-old self? What seemed impossible to him at the time but he then accomplished anyway?

• Adam always knew he liked science, but he didn't think a career in science would likely to pan out.

• He figured one day he'd have to grow up and get a job.

• "So I guess I would say to myself, “Keep following your passion.” I know it's cliché but in my case, it was literally true. Don't give up until the door’s been slammed a hundred times." - Adam Riess