The expanding universe: discovery, controversies, and hope

We’ve known that there is a universe outside the Milky Way, and that it is expanding, for less than a century.

“Throughout the entire history of the universe, of knowing it’s expanding, there have been a tremendous number of controversies over it, and there’s still one that persists today,” said astrophysicist and author Ethan Siegel. Siegel, author of Beyond the Galaxy: How Humanity Looked Beyond Our Milky Way and Discovered the Entire Universe (World Scientific Publishing, 2015), spoke at last week’s meeting of the Rose City Astronomers in Portland, Oregon.

The controversy actually goes back to before the expansion was observed, to Albert Einstein. His equations describing general relativity suggested that gravity would collapse the universe onto itself, and as he believed the universe was static, he threw in a “cosmological constant” to push back against gravity. Einstein later called that his biggest blunder, though some wanted to let him off the hook for it when dark energy was proposed to do the exact same thing.

“I am here to tell you that this was Einstein’s reasoning and throwing this in there when he did was a super big blunder because the universe isn’t static,” Siegel said. Einstein should have trusted his theory, he said, and taken it to the next step.

The universe is expanding

By the 1920s Edwin Hubble observed a Cepheid variable star in the Andromeda “nebula” that indicated that it was far outside the Milky Way and a galaxy in its own right. Astronomers were also studying redshift as an indication for the speeds at which galaxies were receding from us. Siegel explained that through this, Hubble determined that the universe was expanding at a rate of 600km/sec/Mpc (kilometers per second per megaparsec.) This became the Hubble constant. But it wasn’t so constant.

Siegel noted that, knowing the size and expansion rate of the universe, you can figure its age by running the numbers in reverse and going back to the beginning, to the Big Bang. The resulting calculation determined that the universe was about two billion years old. Geologists at the time had already pegged the age of the Earth as at least four billion years.

“This was a problem for Hubble, because the universe isn’t allowed to be half the age of the Earth,” Siegel noted. “Either this expansion rate is wrong and this age for the universe is wrong, or the age of the Earth is wrong.”

It turns out that Hubble’s main mistake was in figuring that all variable stars are alike. Siegel said Walter Baade came along in the 1940s and discovered that they are not. Finding that most of the Cepheids Hubble had looked at were non-classical, they re-ran the numbers from Hubble’s data.

“As you accumulate more knowledge, as you accumulate a better understanding of what you’re actually looking at, you can go back and get more useful science out of this data,” Siegel said. This second look doubled the distance to these stars and reduced the value for the Hubble constant to 270km/sec/Mpc. This in turn put the age of the universe at five billion years.

“That’s better,” Siegel noted. “The universe is older than Earth. That’s one problem solved.”

Narrowing it down

Dr. Ethan Siegel, creator of the “Starts With a Bang” blog, gave
a talk about the age and size of the universe to the Rose City
Astronomers February 20. Photo: Greg Scheiderer.

As time went on astronomers developed the “distance ladder” for determining the vast distances in the universe. You first measured the distance to Cepheid variables within the Milky Way, then gauged the distances to other galaxies using Cepheids spotted there. Type 1a supernovae could be spotted really far out. As we learned more about the stars we got a little better at figuring distances.

Things got really interesting in the 1960s, according to Siegel. We discovered that we could determine the ages of stars by measuring their color and brightness. The Hertzsprung–Russell diagram told us that the oldest stars were between 14 billion and 16 billion years old, significantly older than the age of the universe determined by Baade. Astronomer Allan Sandage, who as a graduate student was an assistant to Hubble, came along and said you needed two things to make the universe that old: it had to be low enough in density to make a vast expansion, and the expansion rate had to be low.

Dueling Hubble constants

This, Siegel said, was where the controversy came in. Sandage said the expansion rate would have to be between 50-60km/sec/Mps. Rival astronomer Gérard de Vaucouleurs of France put it at around 100km/sec/Mpc. The race was on to make observations to see which group was right. Amazingly enough, each group’s observations matched up with what they thought the answer would be.

“This just goes to show that you cannot have the same people making the same measurements and trust them,” Siegel said. “This is why you need independent confirmation.”

It turns out Sandage and de Vaucouleurs were both wrong. There’s still no agreement on the right answer, but the disagreements are getting closer together. Sigel said the Hubble Space Telescope’s improvements in measuring the size of the universe return a value of 74±2km/sec/Mpc. The Planck mission’s observations of the cosmic microwave background radiation suggest 67±1km/sec/Mpc.

“There is a fight over the results like there always seems to be, because we are scientists and we cannot agree on anything,” Siegel said. “That is good, because questioning is what keeps us moving forward and what keeps us learning more.”

“The way we’re going to get there is with more and better data,” he added.

Better data

The better data will come from missions such as the European Space Agency’s Gaia, the James Webb Space Telescope, WFIRST, and the Large Synoptic Survey Telescope, which combined might improve our parallax measurements of cosmic distances by a factor of ten. We might also weed out faulty assumptions in the earlier work or get more accurate insights into the balance between matter and dark energy in the universe.

“If we can wait until the next decade, we might see that 74 number come down, we might also see the 67 number come up,” Siegel said. “The point is uncertainties are going to be reduced by more and better data.”

Siegel said that right now it’s pretty much agreed that the universe is about 13.8 billion years old and consists of about 30 percent matter and 70 percent dark energy. But the minuscule pluses or minuses can lead to huge fights.

“When that data comes in at last we will know exactly how fast our universe is expanding, how old it is, and what it all means for both our cosmic origins and our cosmic fate,” Siegel concluded. “That’s pretty good stuff.”

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In the podcast linked below Siegel covers much of the topic matter of this article and his talk. His new book, Treknology: The Science of Star Trek from Tricorders to Warp Drive (Voyageur Press, 2017), is scheduled for release in October.

Threading the needle with Cassini at Saturn

The hugely successful Cassini mission to Saturn will come to a fiery end in September, and you can hardly blame NASA for going a little Star Trek on us.

Ron Hobbs. Photo: Greg Scheiderer.

“We’re going somewhere where no spacecraft has ever gone before, into this region between the glorious rings of Saturn and the cloud tops of the planet,” said Ron Hobbs, a NASA Solar System Ambassador, at this month’s meeting of the Seattle Astronomical Society. After 22 orbits through the eye of that needle—a 2,500-kilometer-wide gap—they’ll splat Cassini into the planet and burn it up.

“Now that we’ve discovered that there’s at least one moon, and maybe several, that could have the conditions for life, it’s very important to not leave a derelict spacecraft orbiting around Saturn,” Hobbs noted. “One of the important things at the end of the solstice mission will be to dispose of the spacecraft.”

The second extended mission of Cassini was named solstice because it is almost the beginning of summer in Saturn’s northern hemisphere.

Let’s do science

Before they crash Cassini, they figured there was some time to do some great science in that place where no spacecraft has ever gone. Most importantly, they will get a better picture of the internal structure of Saturn and examine its ionosphere, inner radiation belts, and auroral region.

“This would have been worth sending a spacecraft to Saturn for just that measurement,” Hobbs said, noting that it is essentially what Juno is doing at Jupiter. They’ll also check out the particles of Saturn’s D ring at close range, and be able to better gauge the mass of the ring system, which will help pin down its age.

“I can’t wait for the pictures,” Hobbs added. “The pictures that come out of this mission are just going to be spectacular.”

Shooting the gap

Hobbs said NASA has been using interactions between Cassini and Saturn’s moon Titan to nudge the spacecraft’s orbit to where they want it to be.

“Titan is really the only object in Saturn orbit that has enough mass to allow it to do gravitational assists and re-direct its orbit,” he said. “That allows [Cassini] to change its orbit and change the plane of its orbit.”

This graphic shows the closest approaches, or periapses, of
Cassini’s final two orbital phases.The ring-grazing orbits
are shown in gray; grand finale orbits are shown in blue.
The orange line shows the spacecraft’s final plunge into
Saturn. Credit: NASA / Jet Propulsion Laboratory – Caltech

In late November a brush with Titan dropped Cassini’s perichron—the point closest to Saturn in its orbit around the planet—down to just outside the F ring. In April, another Titan flyby will drop that perichron down to between the D ring and Saturn’s cloud tops.

“That’s when it’s going to get really exciting,” Hobbs said. Cassini will do 22 “grand finale” orbits through the eye of this needle, each lasting six days, collecting science data until one final encounter with Titan puts the spacecraft on a trajectory to splat into the planet on September 15.

It’s amazing how much planning and politics went into all of this. Hobbs said the actual trajectories of the orbits for this grand finale were determined a little over three years ago. Ever since then there’s been a spirited discussion between scientists, engineers, and mission leaders about what science to do to get as much data as possible out of the final mission. That determination was just completed last month.

“The spacecraft drivers are now writing the code for these orbits,” Hobbs said. That will tell Cassini where to go and where to point its instruments to make the observations as planned.

A good ride

Hobbs noted that Cassini was launched in October 1997, and so will end its mission just shy of twenty years in space.

“Without a doubt it has been one of the most successful and audacious missions NASA and the international community have operated,” he said. “This is going to be one of the highlights of space exploration in the last couple of decades.”

Pushing for IDA membership

Kelly Beatty thinks more amateur astronomers should be members of the International Dark-Sky Association (IDA), and he puts his money where his mouth is on the issue. Beatty, a senior editor of Sky & Telescope magazine and a board member of the IDA, made an offer to waive his usual fee for speaking at the recent Seattle Astronomical Society banquet if the group could sign up at least ten new or renewing IDA members. At last word they’d added at least a couple of dozen.

Still, Beatty noted at the January 28 banquet that while there are roughly a quarter of a million amateur astronomers in the United States, the IDA has only about 3,000 members.

“That means that roughly one in a hundred amateur astronomers across the U.S. are members of IDA,” Beatty pointed out. “Isn’t that pathetic?”

“What other group has more to gain or lose from the success of the IDA and our dark sky preservation efforts?” he asked.

Beatty

Beatty noted that LED street lighting is a major issue, and one on which regular citizens can help. If your city or town hasn’t converted street lights to LED yet, it probably will soon. LED street lights can be cheaper in a couple of ways. They consume less energy than typical street lights (though this paradoxically can cause a municipality to just buy more light), and the fixtures have a longer expected life span. What is important is that cities use fixtures that are at a color temperature of 3,000 kelvins or less. This provides warmer light with less blue in the spectrum. Blue light brightens the night sky more than any other color of light, and exposure to blue light at night has also been shown to harm human health and endanger wildlife.

Beatty said that the city of Phoenix recently decided to install 2,700-kelvin streetlights, Montreal dropped plans to install lights at 4,000 kelvins, and the entire state of Georgia is going with 3,000-kelvin lights.

“You have the power to make a difference in this fight against light pollution, individually and collectively,” Beatty said. “It’s not that people are opposed to doing the right thing, they just don’t know. It’s an education. So if you inject yourself into the process you can and will make a difference.”

IDA’s page about outdoor lighting basics and its LED practical guide have lots of useful information. Oh, and you can sign-up online. There’s a $15 annual membership for students, and standard memberships start at just $35.

Kelly Beatty's history of Pluto

The history of Pluto goes way back before it became a tiny twinkle in Clyde Tombaugh’s blink comparator. Kelly Beatty, a senior editor at Sky & Telescope magazine, told the story of Pluto in his keynote address Saturday at the annual banquet of the Seattle Astronomical Society.

Kelly Beatty, right, with Seattle Astronomy’s Greg Scheiderer
at the annual banquet of the Seattle Astronomical Society
January 28, 2017. Astronomy guys love their
astronomy ties. Photo: Greg Scheiderer.

In a way, according to Beatty, the hunt for Pluto dates back to the late 1700s. The Titius–Bode law (since repealed) of the distances to the planets from the Sun worked well, with one exception: according to the law, there should be a planet between Mars and Jupiter.

Thus a group of astronomers calling themselves the “celestial police,” led by Franz Xaver von Zach, set out to find this elusive object. They did it; on New Year’s Day, 1801, Giuseppe Piazzi discovered Ceres. It wasn’t long before Juno, Vesta, and Pallas we found. At first all four were labeled planets, but now they’re known as the four largest asteroids—and possibly the first celestial objects to be demoted in status.

Dumb, fool luck

Blink comparator used by Clyde Tombaugh at Lowell
Observatory to discover Pluto.
Photo: © User:Pretzelpaws / Wikimedia Commons
 CC-BY-SA-3.0.

Later, because of irregularities in the motion of Uranus, astronomers predicted another planet out beyond its orbit. But even after the discovery of Neptune in 1846, anomalies remained. Percival Lowell and William Pickering predicted there was yet another planet beyond Neptune. The hunt was on for Planet X, and Pluto was finally discovered by Clyde Tombaugh in 1930. We soon learned that Pluto was pretty small, which lent some irony to its discovery.

“Pluto didn’t have any effect on Uranus and Neptune at all,” Beatty said. “It turns out that the mathematics were incorrect, the positional accuracy of those early observations was bad. There was no basis to the prediction whatsoever, and by dumb, fool luck Clyde found the planet Pluto that he had been seeking within about six degrees of the predicted position. Freakingly by accident.”

We didn’t know a whole lot about Pluto for a long time. The best photos we could get were fuzzy Hubble Space Telescope shots. Astronomers found methane ice on Pluto in 1976, and its moon Charon was discovered in 1978. Pluto’s atmosphere was discovered in 1988 when it occulted a star.

Pluto on thin ice

“In 1998 the bottom fell out of the pro-Pluto movement,” Beatty said. The beginning of the end was the discovery of another distant object in what we now call the Kuiper Belt. Astronomers figured that there had to be more out there than just Pluto, and we now know of more than 1,800 of them. Many of these objects are locked in a 3:2 orbital resonance with Neptune, just like Pluto.

“Not only is Pluto not alone, it’s not even unique in its orbit,” Beatty said. “Things did not look good for Pluto and its planet status.”

The International Astronomical Union (IAU) started hearing chatter that Pluto should not be a planet, and in 1999 it passed a resolution declaring that it still was. Brian Marsden, who headed the minor planet center of IAU, really wanted to classify Pluto as an asteroid, according to Beatty.

Then, in 2005, Eris was discovered. At the time it appeared to be bigger than Pluto, though we now know it is slightly smaller. It was bureaucracy that finally knocked Pluto off the planet list. Different committees at the IAU name planets and asteroids, so to decide to which committee to refer the new discovery for naming, they had to decide what it was. This led to the new definition of planet, under which neither Eris nor Pluto fall. The IAU declared Pluto to be a dwarf planet in 2006.

Beatty is not fond of the IAU definition of planet: an object that orbits the Sun, has enough mass to be round, and has “cleared the neighborhood of its orbit.”

“It’s a really stupid definition,” Beatty said, mostly because it’s hard to know the mass of faraway objects, and so the definition is difficult to apply. Plus he finds it puzzling that a dwarf planet is not a planet.

“We have dwarf stars which are considered stars.” he pointed out. “We have dwarf galaxies that are considered galaxies. A chihuahua is still a dog.”

New Horizons

New Horizons close-up of Pluto, one of the first and most
iconic images from the mission. Photo: NASA.

Planet or not, the New Horizons flyby of Pluto in 2015 gave us a ton of new information about it and its moons. Beatty shared numerous photos of and findings about Pluto from the mission. It’s mostly made of rock, and might have liquid water below its surface. The surface features are mostly hard-frozen water ice, with a little frozen nitrogen, methane, and carbon dioxide mixed in.

Most fascinating is evidence of geology happening right now in the form of flowing nitrogen ice.

“Pluto’s surface, against all odds, out in the frozen corner of the solar system,” Beatty marveled, “has flowing glaciers on it.”

The last of the Pluto data from New Horizons arrived on Earth back in October, but the mission isn’t over. The probe is headed out for a look at the Kuiper Belt object 2014 MU₆₉, at which it will arrive on January 1, 2019.

Beatty said this great new data about Pluto was worth the wait.

“We finally know what this planet/dwarf planet/interesting world looks like,” he said. “It was a 30-year effort from the time the Pluto missions were first conceived until we finally got out there. Some of the people involved, like Alan Stern, were there every year of the way, and boy, what a rich reward they have for their efforts.”

Start saving: flying to space with Blue Origin

If there’s any anti-science sentiment around these parts it wasn’t evident last Friday at Peddler Brewing Company in Ballard, where some 500 space enthusiasts packed the brewer’s beer garden—yes, we were sitting outside, in Seattle, in January—to hear from employees of Kent-based Blue Origin about the company’s latest testing and the prospects for an affordable ride to space any time soon. The event was the latest installment of Astronomy on Tap Seattle, organized by graduate students in astronomy at the University of Washington.

L-R Nicholas Patrick, Dan Kuchan, and Sarah Knights of Blue
Origin after their presentation at Peddler Brewing Company.
Astronomy on Tap photo: Brett Morris and Nicole Sanchez.

“Our ultimate mission is to have millions of people living and working in space,” said Sarah Knights, outreach coordinator at Blue Origin. “The way that we’re focused on that is to lower the cost of human spaceflight, and one of the ways to do that is to make vehicles reusable, so that’s our primary focus right now.”

Blue Origin’s current test vehicle is the New Shepard, a capsule and vertical takeoff/vertical landing rocket. It’s powered by the BE-3, for Blue Engine 3, which is fueled by liquid oxygen and liquid hydrogen and can deliver 110,000 pounds at full thrust. As suggested, the rocket blasts off, and then lands softly back on Earth.

“As it’s coming back down we can throttle it back to about twenty percent of its full throttle, so that means that as the propulsion module is coming down we can have an equal thrust-to-weight ratio, find the landing pad, and very gently set it down,” Knights explained.

Blue Origin safety test

Dan Kuchan, Product Development Team lead engineer on the New Glenn program at Blue Origin, said the most recent test of New Shepard, conducted in October, was of the vehicle’s full-envelope crew escape system.

“That means that if the rocket at some point decides that we can’t go to space today, the crew capsule can jettison itself and get out of Dodge,” Kuchan explained. It was the first such in-flight escape test for a space vehicle since 1965, during the Apollo program. Kuchan showed this video of the flight test during the presentation.



“That was an awesome test and it capped off the fifth flight and landing for that booster,” Kuchan said. “The system worked flawlessly.”

Astronauts soon

So far New Shepard has only flown without a crew, but they hope to have astronauts on board soon. That’s where Nicholas Patrick comes in. Patrick, a former NASA astronaut who flew on space shuttle missions for construction of the International Space Station, is now Blue Origin’s human integration architect.

“I’m responsible for worrying constantly about every aspect of flying on our spacecraft,” Patrick said. That includes everything from meeting rules and regulations, testing to make everything right, and every imaginable human factor.

They chose a capsule rather than a winged vehicle like the space shuttle partly for safety. The smaller capsule can get away from the booster quickly, as demonstrated in the video above. Patrick said it’s also a better way to travel.

“For those who are paying to ride aboard a New Shepard in the coming years this is a more authentic rocket flight experience than most other ways you could get to space,” he said.

The New Shepard capsule has big windows, the largest ever flown in space, and all passengers will have one of their own; there are no middle seats on New Shepard. Suborbital flights will last about eleven minutes, and passengers will be weightless for several minutes.

“We want to give them the best imaginable experience,” Patrick said. He showed this video animation of what a New Shepard flight will be like.



“That’s a New Shepard flight that we hope will be available to anybody who can get in and out of the capsule, who can tolerate the three Gs on ascent, and a little higher on descent,” Patrick said. “So start saving.”

At what cost?

How much to save is a question that Patrick said hasn’t yet been answered.

“Obviously everybody’s goal is to get this price down a long way,” he said. “We’re not going to get millions of people living and working in space by charging a quarter of a million or a hundred thousand dollars just for a suborbital flight.”

The question of when people will fly on New Shepard also hasn’t been answered.

“We’re not driven by that kind of schedule,” Patrick said. “We’re driven by our flight test program and the success or challenges we face in each of those tests.”

“What I can tell you is that I expect we’ll be flying people in the next year or two,” he added.
Kuchan noted that, in a way, New Shepard astronauts will be human guinea pigs.

“New Shepard and everything we’re doing, sending tourists into space, is all a way for us to practice and master landing a reusable rocket, and using it in a commercially viable way, so that over the next 50, 100, 200 years we can move civilization deeper into space,” Kuchan said.

Next steps: a bigger rocket

Blue Origin’s motto is gradatim ferociter—step by step, ferociously. The next step for the company is on the drawing board now: the New Glenn, which will get payloads into Earth orbit. The New Glenn will dwarf the New Shepard. While the latter is powered by one BE-3 engine that delivers 110,000 pounds of thrust, the New Glenn will have seven BE-4 engines that deliver 550,000 pounds of thrust each. That’s a lot of oomph. Again, there’s no totally firm timeline, but Kuchan said they’ve been asked to deliver the rocket by the end of the decade, and added that they plan to do so. It’s another step on the way to having millions of people living and working in space.

“Every single decision that gets made at Blue Origin is weighed against that ultimate goal,” Knights said.