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Ethan Siegel
Works at NASA's The Space Place
Attended University of Florida College of Liberal Arts and Sciences
Lived in Bronx, New York
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Ethan Siegel

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“If antimatter falls up, we would be tremendously surprised. A lot of things would be wrong. E=mc^2 would be wrong, for one, or gravitational and inertial mass would not be identical. We're doing the experiment because we have to check all our theories and expectations against the evidence, but we have been attempting to measure this for maybe 50+ years now, and haven't been able to create and track neutral antimatter precisely enough to check it out. We will keep trying, and hopefully we'll verify that it falls in a gravitational field just like we expect.

We see antimatter ejecting out of galactic "jets" with the same velocity profiles as we see for normal matter, so we do expect it to behave gravitationally just like matter does. But we don't know for certain until we check. Still, if it turned out that antimatter falls up, I would say it'd be the biggest surprise and discovery of the 21st century. I'll keep watching.”

Ever wonder if antimatter falls up? If black holes could be dark matter? If life in other galaxies is different from our own? Or if there’s any evidence besides spinning galaxies for dark matter halos? Come find out all this and more on this edition of our comments of the week!
“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.” -Neil Armstrong This past week saw a whole lot of interesting things happen, including…
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Interesting. I never thought of antimatter having a repulsive reaction to gravity. As far as I know, it has the same mass, but opposite charge of regular matter. In particle accelerators, the short lived antimatter created in the collisions, veers off in opposite directions of regular matter. But it must be gravitationally bound, because it doesn't have anti-mass.
I think E=mc² is safe, (for now).
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"I have an astronomy question, and it is basically this: how many independent ways can we measure the age of the universe?"

The Big Bang was the birth of all the matter and radiation in the Universe, and signifies the beginning of what we know as all of existence. Yet it didn't happen an infinite or even an indeterminate amount of time ago: it happened precisely 13.81 billion years ago, with an uncertainty of just 120 million years. But despite all of our observations and data about the Universe, there are just two independent lines of evidence that lead us to that conclusion. At least they agree!
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+Bear Field Just because you have a grudge against someone or something that you associate with religion does not make it our problem here. You don't like the menu the door is ahead of you. I don't force you to believe. I say what I know and you can just take it as that. The fact that it bothers you shows you have an emotional attachment to religion.
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"While any one piece of evidence on its own may be argued away or can replace dark matter with an alternate explanation, the full suite of evidence points towards the incontrovertible existence of dark matter.

Any Universe without it simply wouldn’t look like ours."

Everywhere we look in the Universe, we find more Universe that looks an awful lot like we do, with planets, stars, galaxies, groups and clusters similar to our own. Yet the Universe we see isn't all of what's out there, with normal matter (or any of the Standard Model particles) unable to explain even a simple majority of what we observe. Instead, we require five times as much dark matter to explain the mass we see, with at least seven independent lines of evidence supporting that inescapable conclusion.
With the full suite of evidence, there’s no escaping dark matter.
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Omg no gravity
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"Grand design spirals (which make up only about 10% of galaxies) tend to have 2 or 4 strong spiral arms, and they’re often extremely photogenic and pleasingly symmetric objects in the sky. But the method of forming and maintaining those arms has been remarkably hard to explain.

The problem with explaining spiral arms lies fundamentally in that the components of a galaxy rotate at different speeds; the inner part of the galaxy rotates faster than the outer parts. So the easiest explanation — that the arms are actually just areas of the galaxy that are physically more dense, and a fixed association — doesn’t work."

Most mental images of galaxies invoke thoughts of two giant arms, spiraling out from the center and wrapping around, covered richly in stars. Yet this picture, though incredibly common, represents only about 10% of galaxies. Moreover, the galaxies that do have two grand, spiral arms won't have them for very long, as the classic picture we have of spirals represents only an intermediate stage in galaxy evolution.
Outwards from a galaxy’s center, two arms wind round-and-round. But why?
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Reach to the expanding Universe without anymore damage to ozone layer it is safety belt only human body of our globe
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"During the day hours, a series of images from the specific location are shown on the display. We replace the missing background and create a magic dimensional window. A dynamic motion parallax effect occurs as the vehicle passes the location."

"Unvertising" artist Brian Kane is turning ClearChannel billboards into visual simulations of the lost, missing natural world. His project, Healing Tool, showcases the nature that would be present if the billboard (and urbanization) were absent. And you've got to see what it looks like at night!
How artist Brian Kane is bringing a moment of peace to one of the most urbanized, ad-saturated areas in the world.
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"Even outer to Iapetus lies Phoebe, a smaller moon that’s most likely a captured object from the Kuiper belt. Unlike all of Saturn’s other moons, Phoebe orbits in the opposite direction, is far more distant, and most importantly, is very, very dark. In addition, Phoebe has been emitting a steady stream of particles for a very long time, as the Sun’s radiation and minor collisions are strong enough to kick dust grains off of Phoebe’s loosely-held-together surface."

When Giovanni Cassini discovered Saturn's moon Iapetus in 1671, he was puzzled to find that it was easily visible on the western side of the planet, but unable to be seen along the eastern side. Only 34 years later did he find it on the east side, finding it two full magnitudes dimmer. His theory was that Iapetus was locked to Saturn, and that it had one light hemisphere and one dark one. It took another 300 years, but now we finally know what caused this two-toned world: a captured Kuiper belt object is to blame!
The most unusual looking moon has a dark side, all thanks to a failed comet that was captured by Saturn long ago.
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Una buena explicación. Gracias.
A good explanation. Thank you.
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Ethan Siegel

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"The reason it doesn’t occur is because all of its isotopes are radioactive, with the longest-lived ones having a half-life of just a few million years. Even if the Earth was created with significant amounts of it, the odds are minuscule that there’s even one atom of it left by now, after more than four billion years have passed. In fact, it’s only from the decay of materials like Uranium ore (below) that Technetium is naturally produced, with each gram of Uranium giving rise to approximately one picogram (10^-12 g) of Technetium."

Beyond hydrogen and helium, every atom of every element we have on Earth was made in a star, processed in space and then finally condensed to form our world some 4.5 billion years ago. All the elements of the periodic table up through Uranium are found on our world, except one: technetium, element 43. But technetium is found in (some) stars, thanks to an amazing reaction: the s-process.
When it comes to the elements in the periodic table found throughout the Universe, it's only the first two that originated from the Big Bang: hydrogen and helium. Everything else was formed from stars, whether: fused in their cores, from lighter elements into heavier ones, built in supernovae, where the tremendous energy-and-particle [...]
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+Viking Knight How do you like that piece of technology you are using to type all this nonsense,did the church supply you with it,or was it some scientist,engineers and the like,delusion can be treated buddy,seek some help.
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"The craziest thing of all is that if you wait long enough or look precisely enough, you’ll find that every star will undergo a period of variability in its life. Like many things in this Universe, the only constant is change."

Those constant, fixed points of light in the night sky — the stars — turn out not to be so constant if you looked with great precision at them. A star like our Sun varies in brightness, periodically, by about 0.1% over the span of a few years, but many stars vary by 99% or more from brightest to dimmest. For centuries, we knew of only a handful of these objects, yet now they’re known to be commonplace. Here's what causes their behavior and underlies it, along with the story of their discovery.
The “constant points of light” in the sky are often anything but.
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Very informative.
Always a pleasure,Thank you Ethan.
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“6. It’s responsible for the structures in the universe.

Since dark matter doesn’t interact much with itself and other stuff, it’s the first type of matter to settle down when the universe expands and the first to form structures under its own gravitational pull. It is dark matter that seeds the filaments along which galaxies later form when visible matter falls into the gravitational potential created by the dark matter. If you look at some computer simulation of structure formation, what is shown is almost always the distribution of dark matter, not of visible matter. Visible matter falls into, and hence, is assumed to follow the same distribution at later times.”

When it comes to dark matter, the mysterious substance that makes up the vast majority of the mass in the Universe, there's a whole lot we don't understand or know about it. You might think that there are so many unknowns that are so huge that -- quite reasonably -- perhaps it doesn't exist at all, and there's some other explanation for the behavior of masses on galactic scales and up? And yet, you can't make that leap unless you've honestly (and scientifically) considered the full suite of evidence and facts that speak to the question of dark matter's existence. Sabine Hossenfelder does exactly that.
And if you know all ten, you’ll understand just what it is… and isn’t.
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Could not dark matter be a manifestation of a higher dimensional space wherein we have no way to see or comprehend it's true structure and composition and only can perceive a mere echo of its effects in "classic" space?

We must not let our perceptual limitations dictate reality.
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“Ultraviolet images from Swift and GALEX showcase the hottest, youngest, bluest stars, which are found in clusters along the spiral arms and in the very center. In the infrared, from WISE and Spitzer, the cool gas shows where future generations of stars will form next. The shorter infrared wavelengths also highlight stars irrespective of whether galactic dust obscures them or not.”

If we want to know where new stars have formed, where the hottest ones are, where new ones will be forming and what lies behind the dust, we have to look in wavelengths beyond what our eyes can see. Yet our greatest space observatories can do exactly this, at both longer and shorter wavelengths, revealing a whole galaxy’s worth of secrets!
If you want to understand how a galaxy works, visible light is just the start.
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An amazing amount of information the EM spectrum delivers to us.
For centuries all we were aware of was the tiny slice of visible light.
"The answers have been there all along - we just didn't know how to read them."
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"[T]here are pros and cons to Earth-sized planets orbiting in the habitable zones of M-stars. The pros are easy: M-stars are more numerous, they’re less likely to have giant worlds in there, they’re longer lived that the Sun, they’re more stable in luminosity over time than the Sun, they give off less ionizing radiation, and their planets are in closer orbit and thus better protected from chance encounters originating from interplanetary or interstellar space.

But the cons are rough:

* more frequent and nastier solar flares,
* less energy available from starlight/sunlight for spurring life processes,
* and tidal locking is a much greater danger at such close distances."

Are Sun-like stars the best place to look for Earth-like worlds?
Is asteroid mining for real?
How do we know that pentaquarks are really bound states of five things, and not a meson and a baryon just found together?
Check these (and more) out on our comments of the week!
“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn’t feel like a giant. I felt very, very small.” -Neil Armstrong This past week was the 46th anniversary of the first Moon landing…
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+Ethan Siegel I see, interesting behavior.
Thank you for your time, and I look forward to reading Beyond the Galaxy!
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"How long would it take for stars to cool down after they have exhausted their nuclear fuel? Will there be any ‘black’ dwarfs? Are there any today?"

While the stars exist in tremendous numbers (some 10^23+ in our observable Universe) and great varieties, every star that ever has shone or will shine will someday run out of fuel and die. When that happens, the inner core of the star contracts down to form a tiny, degenerate but very hot object. But even so, no object with a finite amount of energy can shine forever. At some point, even those stellar remnants will cool down out of the visible portion of the spectrum. But how long will that take, how will that happen, and has the Universe been around long enough (yet) so that such an object exists? Answers here.
Even the dead stars still shine today, and will for a long time. But they, too, will fade to black.
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Yes, this would be called an Iron Star - some of these stars have already been detected and are still classified as Brown Dwarfs, but they are in essence Iron Cores with a small energetic atmosphere - not the nuclear furnaces of real stars, but simply an Iron Core with a thin atmosphere that is super heated from the extreme energy of the star - in theory if nothing is every caught in their gravity, not even dust they will stop emitting visible light - but because they are so dense and energetic they will still emit wave particles - 

Iron resists the decay of time the best so in theory the Universe will become nothing more than a large marble sack full of iron balls... in a long long time - though there are other forces at play that will render our current concepts of time and space obsolete
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Work
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Theoretical Astrophysicist / Writer / Educator
Employment
  • NASA's The Space Place
    Columnist, 2013 - present
  • Trap!t
    Head Editor: Science/Health, 2011 - present
  • Starts With A Bang!
    Science Writer, 2008 - present
  • Lewis & Clark College
    Visiting Assistant Professor of Physics, 2009 - 2011
  • University of Portland
    Professor/Lab Coordinator, 2008 - 2009
  • Steward Observatory/University of Arizona
    Postdoctoral Research Associate, 2007 - 2008
  • University of Wisconsin
    Faculty Assistant, 2006 - 2007
  • University of Florida
    Teaching/Research Assistant, Fellow, 2001 - 2006
  • King/Drew Medical Magnet High School
    Teacher, 2000 - 2001
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Bronx, New York - Yonkers, New York - Evanston, Illinois - Torrance, California - Gainesville, Florida - Madison, Wisconsin - Tucson, Arizona - Portland, Oregon - Houston, Texas - Rome, Italy
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Science writer, professor and theoretical astrophysicist
Introduction
Theoretical Astrophysicist, Science Writer and Communicator, expert in (some aspects of) dark matter and dark energy, physical cosmology, and sometimes professor, teacher and educator.

Creator and writer of Starts With A Bang!, the 2010 Physics Blog of the Year! Author of over 1,000 articles, featured in Esquire, the St. Petersburg Times, ESPN.com's Page 2, and many others.

Competitive beardsman and amateur acrobat / halloween-costumer extraordinaire.
Education
  • University of Florida College of Liberal Arts and Sciences
    Physics, 2001 - 2006
  • Northwestern University
    Physics, Classics, Integrated Science Program, 1996 - 2000
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