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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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"...here’s what I want you to do. Take your cellphone and call your friend that you’re actually, physically with. Go have them sit in a car while you stand outside the car. Have a conversation with them on your cellphone and watch their lips move, and pay attention to when you hear their voice in your phone versus when you see their lips move. That’s your evidence, right there, that the Universe is not instantaneous."

With extra scientific bonus questions about adaptive optics, the Universe's age, how perfectly smooth it is, time delays, the strong force, planetary rings and more! Plus, if you didn't get to see the ultimate fanart someone created of me, you won't want to miss your chance!
“Science is the only self-correcting human institution, but it also is a process that progresses only by showing itself to be wrong.” -Allan Sandage As April leaves us and May commences here at Starts With A Bang, I’m so pleased to inform you that amazing things are happening! Thanks to the support of everyone on Patreon, we’re over…
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Ethan Siegel

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Okay, this is too damn cool!

Thanks to Philipp Dettmer, I now officially have FANART!
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You should commission an Axe Cop piece from this guy.
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"In theory, we know that the speed of gravity should be the same as the speed of light. But the Sun’s force of gravity out here, by us, is far too weak to measure this effect. In fact, it gets really hard to measure, because if something moves at a constant velocity in a constant gravitational field, there’s no observable affect at all. What we’d want, ideally, is a system that has a massive object moving with a changing velocity through a changing gravitational field. In other words, we want a system that consists of a close pair of orbiting, observable stellar remnants, at least one of which is a neutron star."

According to General Relativity, the speed of gravity must be equal to the speed of light. Since gravitational radiation is massless, it therefore must propagate at c, or the speed of light in a vacuum. But given that the Earth orbits the Sun, if it were attracted to the Sun’s position some 8 minutes ago instead of its present position, the planetary orbits would disagree with what we observe! What, then, is the resolution to this? It turns out that in relativity itself, what we experience as gravitation is also dependent on both speed and changes in the gravitational field, both of which play a role. From observations of binary pulsars, a gravitationally lensed quasar and, most recently, direct gravitational waves themselves, we can constrain the speed of gravity to be very close to the speed of light, with remarkable precision.
The speed of gravity is taken to be exactly equal to the speed of light. But is that necessarily true? Here's how we know.
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+Vladimir Vasquez you're most certainly welcome 😀 
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"On the largest scales, the fundamental, tiny amount of energy inherent to space itself — less than one Joule of energy per cubic kilometer of space — is enough to overcome even the gravitational attraction between the most massive galaxies and clusters in the Universe. The result? An accelerated expansion, as the most distant galaxies and clusters move farther and farther away from one another at ever faster rates as time goes on. On the largest cosmic scales, even gravity doesn’t get its way."

But what does it truly mean to be strong? We have four fundamental forces in the Universe: the strong, electromagnetic, weak and gravitational forces. You might think that, by virtue of its name, the strong force is the strongest one. And you'd be right, from a particular point of view: at the smallest distance scales, 10^-16 meters and below, no other force can overpower it.

But under the right circumstances, each of the forces can shine. Up until recently, on the largest scales, we thought that gravitation -- by and large the weakest of the forces -- was the only force that mattered. And yet, when we look on the very largest scales, many billions of light years in size, even gravitation doesn't win the day.

There are four possible answers depending on how you look at the question. Come find out who's the strongest of them all!
Set up the right conditions, and any one force can be the most important. But on the grandest scales of all, who's the strongest?
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All a matter of scale. Excellent article Ethan, thank you!
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"A good friend of mine never knew my profession until we had known each other for almost a year. When we were just talking and I mentioned something about being on the news to explain the landing of the Mars Curiosity rover, he was shocked! I asked him what he thought I did for a living. He told me, “I don’t know, I just assumed you were, like, a janitor or something.”

But you made assumptions (quite negative ones) about what I was (and what I was capable of) based on my appearance, which is my choice. Now that you know that I have an eccentric cosplay wardrobe (which some consider impressive), you still assert that I’m better off trying to distinguish myself through the quality of my work. Can’t I do both, without you negatively judging the quality of one from your distaste of the other?"

A lot of people say a lot of things, both to me and about me. Here's what I think of it all this week!
“I left Earth three times and found no other place to go. Please take care of Spaceship Earth.” -Wally Schirra We’ve made it through another amazing week here at Starts With A Bang, and what many of you might not realize is that there was a fabulous new release thanks to the support of everyone on…
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Ethan Siegel

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"Yet a world that was in between Earth and Neptune in mass and size could take tens of thousands of years to orbit. And as it passed through either the outer Kuiper belt or the inner Oort cloud, it would perturb whatever objects were out there, and create this strange clustering pattern, in ecliptic longitude and latitude, of these Trans-Neptunian Objects."

Is Planet Nine for real? What's the scientific evidence for its existence, and what are we doing to try and find out whether it's a figment of our imaginings or not? Find out all this and more on our latest Podcast! (And if you really like it, consider supporting our Patreon, which enables us to create them!)
Ethan Siegel
Podcast #7: Our Solar System's Planet Nine by Ethan Siegel
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Woot! I'll be listening to your podcasts religiously!....errr I mean, scientifically?
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Ethan Siegel

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“It’s a long shot, but could quantum entanglement be used for communication?”

If you were to send a space probe to a distant star system, gather information about it and send it back to Earth, you'd have to wait years for the information to arrive. But if you have an entangled quantum system -- say, two photons, one with spin +1 and one with spin 1 - you could know the spin of the distant one instantly by measuring the spin of the one in your possession. Are there prospects, then, for entangling quantum particles, placing one aboard a spacecraft and sending it to a distant star, making a measurement at that distant location and then making a measurement here to know what you saw over there? It's an incredible idea to exploit quantum weirdness. While the laws of physics allow you to indeed know the properties of the other member of the pair by making a measurement here, they conspire to prevent you from transmitting information faster-than-light.
On one hand, nothing can travel faster than the speed of light. But the collapse of a quantum wavefunction happens instantaneously. What can we learn from that?
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Thanks, I just added Ursula K. Le Guin to my list of sci-fi authors to follow.
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“If the Universe had the same current properties today but were made of 100% normal matter and no dark matter or dark energy, our Universe would be only 10 billion years old. If the Universe were 5% normal matter (with no dark matter or dark energy) and the Hubble constant were 50 km/s/Mpc instead of 70 km/s/Mpc, our Universe would be a whopping 16 billion years old. With the combinations of things we have today, however, we can confidently state 13.81 billion years is the age of the Universe, with a very small uncertainty. It’s an incredible feat of science.”

When it comes to the Universe, there are some dead giveaways as to what its age is. Its elemental composition changes, the types of stars that are present evolve, the large-scale structure visible to us morphs, grows and ceases, and the temperature of the cosmic microwave background drops, among many other signs. Yet when we put them all together, there are only two methods available to measure the age of the Universe: the measurement of its expansion history and the measurement of the age of the oldest stars. The first is by far the more accurate, at 13.81 billion years (plus or minus just 120 million), while the second validates that picture, with a maximum age of 13-to-14 billion years.
The Universe is measured to be 13.81 billion years old, with a remarkably small uncertainty. But how did we arrive at that number?
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Some cosmologists and authors are too confident in the Big Bang model as there are many stars, globular clusters and galaxies that are older than the age of the universe as according to the creation theory known as the Big Bang. Here is just one story that contradicts the idea that the Big Bang advocates are correct about their confidence in the age of the universe: http://www.dailygalaxy.com/my_weblog/2010/05/massive-ancient-galaxy-stirs-mystery-is-the-universe-older-than-we-think.html

Also see:
https://sites.google.com/site/bigbangcosmythology/letterevidence

https://sites.google.com/site/bigbangcosmythology/
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"The fact that our atmosphere is layered is crucial to the success of this method. Certain elements are segregated from the others, and are found only at very particular altitudes. One of the elements that’s very rare is sodium, which happens to be concentrated in a thin layer about 100 km (60 miles) up. If you fire a sodium laser into the air, it will excite those sodium atoms found at that particular altitude, which then spontaneously de-excite, creating an artificial light source to be used as an artificial guide star."

If you want to take an ideal image of the Universe, you need to not only minimize your light pollution, cloud cover and build the largest-aperture telescope you can, you also need to take away as much of the atmospheric distortion as you can. Typically, this involved building your telescopes at as high an altitude as possible, or ideally, going to space. However, adaptive optics technology recently (in 2012) surpassed the Hubble Space Telescope in at least some circumstances, and the latest development, of the 4 Laser Guide Star Facility (4LGSF), is poised to blow the old records out of the water.
The atmosphere can be the greatest enemy of astronomers across the world. Thanks to this latest innovation, we're poised to conquer it like never before.
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Ethan Siegel

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“It’s thought that these rings formed by organic compounds from either colliding, destroyed moons or ejecta via the extant moons. The small, innermost moons of Neptune and Jupiter shepherd their great, dusty rings. Contrariwise, Uranus’ rings simply are, consisting of mostly rocks up to 20 meters in size.”

We typically think of Saturn as our Solar System’s ringed world, thanks to its huge, glorious rings spanning nearly three times the diameter of the planet from tip-to-tip. But the other three gas giant worlds have their own impressive ring systems, with Jupiter, Uranus and Neptune boasting four, thirteen and five rings, respectively. While Neptune and Jupiter’s rings are exclusively created and shepherded by their inner, tiny moons, Uranus has a system somewhere in between those worlds and Saturn’s, having been discovered from the ground years before the Voyager spacecraft ever arrived. Go get the full story in pictures, animations and no more than 200 words on today’s Mostly Mute Monday!
Saturn gets all the attention, but the rings of Uranus, Neptune and Jupiter are spectacular in their own right.
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Ur anus, Jupiter & Sir Neptune have rings as well? Nice.
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"[M]y dad and I have been discussing the possibilities of spacecraft like the ones Yuri Milner and Steven Hawking are proposing. My dad speculated on using atmospheric drag to slow the spaceship down once it arrived at a planet. I attest that it would have no chance of slowing down appreciably and would surely result in a giant explosion. Which one is it?"

Earlier this month, Yuri Milner and Stephen Hawking teamed up to announce the Breakthrough Starshot, a $100 million investment in technology that would build a laser array to propel a thin, light "laser sail" spacecraft to approximately 20% the speed of light. If we can achieve these speeds and sufficiently aim these sails at the nearest star systems, we'll arrive at our destinations within a single human lifetime. But we'll still be going at 20% the speed of light when we get there, or about 1,000 times as fast as the meteors that burn up in our own planet's atmosphere. Is there any chance for slowing these spacecraft down once they arrive, or are they doomed to burn up (or miss completely and leave the galaxy) upon arrival? A reverse laser array might work, but anything involving atmospheric drag would be a disaster!
The 'Breakthrough Starshot' aims to send tiny, sail-like spacecraft to nearby stars at close to the speed of light. But how could we slow them down once they arrived?
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how is something the size of a pack of matches going to gather and transmit data back home? how do you aerobrake an object from .2C ?  how do you find the air and transmit the navigation and guide the thing TO the air?  it's ridiculous.
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"You develop an instant global consciousness, a people orientation, an intense dissatisfaction with the state of the world, and a compulsion to do something about it. From out there on the moon, international politics look so petty. You want to grab a politician by the scruff of the neck and drag him a quarter of a million miles out and say, “Look at that, you son of a bitch.”" -Edgar Mitchell

There are a great many world with opportunities for life, both in our Solar System and beyond, and we've only just begun to discover them. Perhaps Enceladus, Europa or Titan harbor some form of life right now, and perhaps Mars or Venus had plentiful lifeforms in the earliest moments of the Solar System. But compared to everything we've found out there, there's still no planet as friendly to life or hospitable to humans as Earth is. It's the fact that we went beyond the Earth and discovered the Universe that's allowed us to appreciate just how rare, precious and special our home world is.
Make the most of it this Earth day, and remember it every day to come!
Our voyages into space have given us some incredible views of the Universe, but perhaps the most important thing we ever discovered was our own world.
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Work
Occupation
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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Previously
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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Male
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