Wednesday, November 02, 2016

What Do We Really Know About Our Universe?

In October alone, scientists published papers in reputable journals questioning what we think we know about the expansion of the universe, galaxy formation, the number of galaxies in the universe, and the number of planets in our solar system.

Among other data, scientists used the galaxies visible in the Great Observatories Origins Deep Survey (GOODS) to recalculate the total number of galaxies in the observable Universe. The image was taken by the NASA/ESA Hubble Space Telescope and covers a portion of the southern field of GOODS.
Image Credit: NASA, ESA/Hubble
If you’re unfamiliar with the process of science, this might be surprising. People have cited the fact that scientific theories has been proven wrong before as evidence that scientists shouldn’t be trusted. Some even use it as an excuse to wave off scientific results that have health and safety implications. However, the fact that scientific theories are challenged and sometimes proven wrong doesn’t mean that the process is broken—it means it’s working.

The late astronomer Carl Sagan said in a 1996 interview with Charlie Rose, “Science is more than a body of knowledge. It is a way of thinking; a way of skeptically interrogating the universe with a fine understanding of human fallibility.”

Just as a zoomed in view can give you a false sense of the big picture, our understanding of nature is refined as we gather more information. However, the skeptical nature of science means that evidence reigns. Interpretations and speculations, even award-winning ones, must match old and new evidence to stay relevant. With this in mind, here is a brief look at four October papers questioning our current understanding of the universe.

The accelerating universe: If you’ve taken physics in the last 15 years or paid attention to the 2011 Nobel prize in physics, you probably learned that the universe is expanding at an accelerating rate. This knowledge is based partly on an analysis of distant supernovae and is key evidence for the existence of dark energy. A couple of weeks ago, an analysis published in Scientific Reports called the acceleration into question. The researchers analyzed a larger number of supernovae than were included in the original study (because we’ve discovered more since then), and their results suggest that the universe may be expanding at a constant rate. Expanding at a constant rate versus an accelerating rate might not sound like a big difference, but it would have serious implications on our understanding of the universe. What happens now? Just what should happen: Other scientists are reviewing this work skeptically to see how it fits in with the initial study and the larger set of evidence for an accelerating universe and dark energy. You can read a response co-authored by 2011 Nobel Laureate Adam Reiss in Scientific American.

How galaxies form: Last week, a team studying distant, ancient quasars announced surprising results in The Astrophysical Journal. Using a powerful new tool to look at 17 of these super bright active galaxies, they noticed that each one is surrounded by a halo of gas made from the intergalactic medium. This was unexpected—previous studies suggested that only 10% of quasars have such halos. The gas also looks to be much colder than it should be according to our models of how galaxies form, around 10,000°C instead of millions. According to a statement by lead author Elena Borisova from ETH Zurich, “It is still too early to say if this is due to our new observational technique or if there is something peculiar about the quasars in our sample. So there is still a lot to learn; we are just at the beginning of a new era of discoveries.”

The number of galaxies in the universe: Few things are more inspiring than the Hubble Deep Field images. Point the Hubble Space Telescope at one of the darkest patches of sky, let it collect light over several days, and the darkness grows into an awe-inspiring collection of active, diverse galaxies. A new census of the deep sky, combining images from the Hubble and other instruments with mathematical models, suggests that there are at least 2 trillion galaxies in the observable universe! That is 10 times more than previously thought. What does that mean? Well, since we are looking back in time when we look at light from such distant objects, this suggests a history filled with galaxy mergers to explore. The results were published in The Astrophysical Journal in mid-October.

The number of planets in our solar system: If you missed our story on evidence for a possible planet nine in our solar system a couple of weeks ago, you can check it out here: Is Planet Nine Pulling Us Closer?

Skepticism is an important part of the scientific process, often leading to thrilling possibilities and prompting deep discussions and further exploration. It’s also important for our way of life more generally, according to Sagan. “If we are not able to ask skeptical questions, to interrogate those who tell us that something is true, to be skeptical of those in authority, then, we are up for grabs for the next charlatan (political or religious) who comes rambling along.”

Kendra Redmond

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