I am Dr. John Mather, Nobel Laureate and James Webb Space Telescope Project Scientist, AMA

1) What is more likely to be the limiting factor on JWST's service life: fuel for station-keeping, or liquid gases for cooling? If JWST runs out of coolants first, is an extended "warm mission" possible?

2) Will JWST actually "park" on L2, or orbit around it like WMAP? Where is WMAP now?

3) Once launched, how long will it take for JWST to arrive on-station? Once there, how much time will be required for calibration, etc., before JWST's science can begin?

1) JWST has no liquid gases for cooling. Our early design had solid hydrogen instead, but we've replace that with a closed-cycle refrigerator using helium gas sealed into the equipment. So, fuel for station-keeping is the limiting factor. By the way we also use the fuel for countering the built-up torque due to solar photon pressure on the sunshield.

2) JWST will orbit around L2 like WMAP. WMAP has been sent off into interplanetary space, so it's orbiting the Sun after a very gentle push-off.

3) JWST arrives around L2 in 2 months, which is about the same time it takes to cool down to operating temperature. We are expecting to be in routine science observing mode 6 months after launch

What is, in your opinion, the most commonly-held misconception people have about planets, stars and outer space?

I think people have a really hard time grasping how empty outer space is, in the sense of immense distances between objects, and immense time spent going from one to another. There's a lot of talk about space aliens as though it were physically possible for them to get here from somewhere else, and (sorry to say this) talk about human travel out of the solar system. We just don't live long enough to do that.

What theory do you believe will remain unproved forever?

Dark energy is probably the hardest thing to study. We have no prediction that it can ever be observed in the laboratory, and the things we have in mind to do in astronomy can only reveal the history of the accelerating expansion, not the reason for it.

But, forever is a long time! I think this just means that theoretical physicists have many ideas and some may work out.

1) What's the next "big step" in terms of space research, after landing curiosity on Mars?

2) What's the best thing about working at/for NASA?

1) Good question! The James Webb Space Telescope is the next big thing in astrophysics, and the Decadal survey produced by the National Academy of Sciences says the next thing after that should be the WFIRST, an wide field infrared survey telescope. Now that the NRO has donated 2 sets of optics to NASA, perhaps one set will become WFIRST. We also have in mind plans for the next great Xray observatory, and a search for gravitational waves using a space interferometer. I think we have at least a century of amazing ideas to carry out.

2) Best thing about working for NASA: thinking about such wonderful possibilities and seeing ideas become reality. Also, I love working with teams of brilliant scientists and engineers every day. Each day is different, and I am so proud of what we are doing together.

Where do you see your field of research in 20 years?

I think we will be swimming in oceans of pictures and data and new discoveries from JWST and other new equipment. Our ground-based telescopes will be about 3x larger than they are today and some of them may have the capability to directly image exoplanets using extreme adaptive optics.

I am currently a high school student at a very engineering focused school and, for the past few years, I have taken a keen interest in advanced physical sciences (e.g. string theory, supersymmetry). I have read multitudes of books, journal articles, and papers by accomplished physicists (including yourself) and I hope to continue these studies as a physics major when I graduate high school.

My question is: Have you ever thought about or regretted your decision to study physics (or specifically cosmology) as a career? Would you, if given the opportunity, want to pick a different field of science to go into?

And one for my parents: Was there ever a time, prior to your employment at NASA, that you couldn't find work or employment associated with your field of study?

Thanks

P.S. I got out of class to send this.

Great! No, I never regretted my choice to study physics. But today, something else might be fascinating too. Every day I read of breakthroughs in biology and technology that are breathtaking in their implications. For instance, people are designing a transistor that has only ONE atom! Then, there's artificial intelligence, which has been harder than people thought, but is making progress.

Nope, I've never been unemployed. But it's always good to be alert to other opportunities.

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Looking at the stars was the beginning of quantitative science, and still propels new advances in technology as well as fundamental discoveries about our history and our place in the universe. People want to know how we got here, are we alone, and where we are going. Astronomy answers part of that.

What do you think is the most exciting thing that the JWST can show to us? what can it help to prove / disprove that we have never had the chance to test before?

I think JWST can produce stunning surprises in many areas. We don't know how galaxies formed or when, we don't know how they got supermassive black holes in their centers, we don't know whether the black holes caused the galaxies to form or vice versa. We can't see inside dust clouds where stars and planets are being born nearby, but JWST will be able to do just that. We don't know how many planetary systems might be hospitable to life, but JWST could tell whether some Earth-like planets have enough water to have oceans. We don't know much about dark matter or dark energy, but we are expecting to learn more about where the dark matter is now, and we hope to learn the history of the acceleration of the universe that we attribute to dark energy. And then, there are the surprises we can't imagine!

How difficult will it be for this telescope to remain at the Lagrangian2 Sun-Earth position? When will it be no longer sustainable to be at the L2 point? I heard it's like trying to balance a marble on a horse saddle.

Also, how worried are you about solar radiation at this location, and what steps are being taken to protect the telescope?

The L2 point: it's unstable, but not very. We need to provide rocket force to achieve an acceleration of a few meters per second, per year! So basically the middle of that horse saddle is pretty darned flat. We have to fire the jets every few weeks, just for a short time.

Solar radiation at L2 is about the same as elsewhere, there's nothing special there. But we do have to protect the electronics from solar flares, which produce energetic electrons and protons that pass through and damage the electronics. So we design and test them to survive the dose, and we have some degree of shielding by the structure. We also fly two of everything where it's logically possible.

Given the difficulty of servicing, wouldn't the amount of fuel effectively determine the longevity of the JWST program? If it does leave the L2 point, how much usefulness remains?

Yes, the end of fuel is the end of JWST's useful life. If JWST leaves L2, it's hard to communicate with it even if it can still point at targets.

Where - outside of the world of science - do you draw inspiration from?

I think history. I know just enough to see the tremendous rate of progress since Archimedes, and I'm eager to see what the next discovery is every day. I also think a bit about human organizations, since science is such a social enterprise. If you read Darwin's Origin of Species, a lot of the text is about thanking people for helping him get information. So scientists have been social since the beginning.

Of all the different scientific fields, why did you choose physics?

Did your Nobel Prize-winning work come about by accident, or did you set out to find exactly what you found?

Along those same lines, what was the moment like when you realized, "Wow, I may actually win a Nobel Prize someday"? Or was it a surprise?

1. It was the one with the greatest unsolved problems! When i was a student, we didn't know much about the elementary particles, but we had a chance to learn so much. Then, it turned out I had a good mind for physics and math, and it was a lot of fun learning how to think about the mysteries, like relativity and quantum mechanics.

2. The Nobel work came by a roundabout path. My thesis project at Berkeley was chosen because it was exciting and I liked the professors. Then it failed to function and I thought I would give up on the cosmic microwave background radiation. Then, I was a postdoc doing radio astronomy and NASA asked for satellite proposals; that was 1974. i said, my thesis project failed, but it should have been done in outer space. So we wrote a proposal and it was chosen.

3. About the Nobel, a lot of people thought the COBE was Nobel-quality work, but I thought, the competition is fierce, and only people like Einstein get on the list. So it was a lovely surprise!

When will the JWST be launched?

We're planning on October 2018, and we've been holding to our schedule for over a year now. We have allowed time and funds to deal with the expected problems, so I'm pretty confident we can make 2018.

Thanks for doing an amazing job! I'm very happy as a Norwegian tax payer to be able to send at least a tiny bit of money your way for JWST.

I don't know if this is really your field, but how do you think the joint financing and cooperation between NASA, ESA and others work? Is it a model for the future? I personally hope we can do great things together.

Thanks! The JWST would not exist as it is today without the joint contributions of Europe, Canada, and the USA, so this can be a model for the future. We don't exchange funds, we just agree on who does what. It's not so easy to arrange, but it's worth it. The results belong to all humanity, and the technology benefits mostly come to the countries that invest in it.

Are you optimistic that the James Webb Space Telescope will help uncover the nature of Dark Matter/Dark Energy that permeates the Universe?

Actually, JWST can only observe the effects of dark matter and dark energy. But to uncover their nature, we need lab experiments, or maybe a comprehensive theory of everything. Both are hard, but worth the effort.

Hi Dr. Mather! I went to your talk at the Vancouver RASC when you came out a year or so ago, and I just wanted to thank you for coming out and giving your presentation.

Hi, thanks for coming out for the Reddit event. So much to talk about!

Do you judge the JWST will be technologically able to partly "substitute" projects that have been recently cancelled or put on hold? If so, to what extent?

What projects do you have in mind?

Mainly projects in exoplanetary research, like the SIM or TPF, for example.

Thanks! JWST will surely be used for exoplanet research, with direct imaging (with coronagraphs) and with transit spectroscopy. It is not a substitute for SIM or TPF, which are still needed if you want to know a lot about exoplanets. Since only around 1% of exoplanets are transiting their stars, we will be missing most of them with JWST transit spectroscopy. A great help for exoplanets would be to survey the nearest brightest stars for transits, like an all-sky version of Kepler.

Will the JWST give us VISIBLE spectrum pictures to view like the hubble?

Yup! JWST coverage begins at 0.6 microns wavelength, which is visible. So some of our pictures may resemble the Hubble pictures, only with different details. Our great hope is to see something completely different from what we can imagine today.

Dr. Mather, What do you see as the real world benefits from all the amazing research and groundbreaking discoveries in the world of physics today? (To include exoplanets, dark matter, particle physics, etc) Have you ever desired to go to space and spend time at the ISS (or further)?

Thank you.

Physics research underlies the progress in almost every area of science, from chemistry to biology to electronics to medicine, and physicists defined the html code for the Internet as we know it. You want to see tumors in your body, try tools from physics. You want to see better, try laser surgery using the math that we astronomers invented to see better on the ground and in space. You want to see oil reserves underground, use sound waves and the math that physicists invented.

Then of course there is the cultural benefit of understanding who we are and where we could go if we try.

Do you think mankind will evolve any further, or do you believe it will require an outside catalyst?

Biologists tell us that mankind is evolving rapidly right now, and they have the genetic evidence to prove it. But clearly our cultural and technical and social environments are evolving even faster, with no end in sight.

1) will you be able to see an evolution of a galaxy using JWST? By looking closer and farther will you see say "x" galaxy over time? say from the light of a billion yrs ago (assuming it is not receding) vs the light of say 14 billion yrs ago?

Actually, we can't observe the evolution of a single galaxy, because we live for only a century or so, and cosmic evolution happens over millions of centuries. So our method is to compare galaxies with each other and see how they look different as we look farther back in time. So far, we see that the galaxies we can see when the universe was young are a lot smaller than today's galaxies, so we think that the early ones grew bigger by merging with each other.

What, in your opinion, are the most interesting hypothesis for the anomalies in the CMB data as observed by the WMAP?

The most interesting anomalies have to do with the largest scale structures, which appear to have a pattern that is a little surprising. So a hypothesis is that the pattern comes from the universe beyond where we can see. Maybe!

Do you believe the end of space exploration has arrived? What is your view on the LHC and its findings on the Higgs Boson particle?

Are you kidding! Of course not. Astronomers alone have a century of projects in mind. And we've barely begun to travel to the planets.

I'm no expert on particle physics but I'm thrilled that a prediction was verified, one that seemed essential to our "standard model" of particles. But we know that model is incomplete, so there is more work to do, both theoretical and experimental.