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Part of my job is to answer questions from High School science teachers, and I love it! These last questions came from a teacher and her year 11/12 students. I thought the questions were good and showed the great depth that some students are thinking at, and also the great interest in science.

I hope I’ve given them justice. This stuff can get quite mind-warpy very quickly!

How do we know how many light-years away we are seeing - as in we have seen stars 13 million light-years away.

Redshift will tell us the velocity of galaxies away from us, then with a calculation as fundamental as c=fλ we can approximate it’s distance. BUT…It’s not a simple as that…of course! There are effects due to our atmosphere, relativity, gravitational lensing, objects in the way, expansion of space etc that get in the way of accurate measurements.

So, we have to KNOW the distance to a whole bunch of objects in order to compare that with others. There are a few ways to do this, either with cepheid variable stars, quasars, pulsars, and parallax. There are a couple of satellites that are tackling the problem with parallax that are very interesting.

Have a look at Hipparcos and Gaia. These two satellites are involved in Astrometry, a very interesting area in astronomy. Literally measuring the stars! The precision is amazing by the way. Gaia can detect a movement of a star of 10 microarcseconds, (or something like that) the equivalent of seeing the length that my hair grows in 10 minutes from a distance of 10 meters. The angle between the smallest division on a protractor is a degree, that’s made of 60 arc minutes, each one of those is 60 arc seconds, and then 10 1000ths of that!

With all of these methods, we can get some very accurate measurements.

The text book states that when the universe was one second old it was at least 1 light-year across but wouldn't that mean it was expanding faster than the speed of light?

YEP! It’s called inflation, and it is not very well understood! We talk about it as if we know what happened, but we really don’t! (like when we talk about how we know what the universe is made of, when we really only know what 4% of it is made of!) The experiment BICEP2 had a pretty close shave with the answer, but there is still some discussion, and of course we need to replicate the experiment.

Due to the fact that we don't understand inflation, we need to observe it and measure it, once that has happened, we can then start to try and figure out some details. So in order to measure it, we've tried to measure the effects of what that period would've done to the gravitational environment. In short, we're searching for gravity waves

If the universe started to collapse - could you travel fast enough to escape and can you exist outside the universe?

No. The idea of existence outside of a universe is, with our current understanding, non-sensical. If the universe collapsed, so would everything in it. The physical space between galaxies, stars, planets, etc would also collapse. Think of the usual stars (dots) on a balloon. If you deflate a balloon, the balloon also shrinks, the stars don’t move independent of the balloon, and interestingly (and in line with the analogy) the dots also get smaller!

The idea of “outside" the universe is not defined in physics (like dividing by 0, you just can’t do it. The idea of putting things into 0 groups is a non-sensical idea!) Space and time break down, we have no way of describing that condition mathematically or physically.

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A recent HSC exam featured a question that could be described as either projectile motion, or angry birds (or both). So I thought a post on the physics of angry birds would be appropriate.

This post was written by Lucy Zhang.

http://www.pocketgamer.co.uk/r/Facebook+and+social/Angry+Birds+on+Facebook/feature.asp?c=37867


Ever since its release in December 2009, Angry Birds has been downloaded 2 billion times across dozens of platforms, filling in countless hours of what would otherwise be tedious boredom. However, during that respite from real life, you would have immersed yourself in a world somewhat removed from the laws of physics. Instead, this parallel universe obeys different laws to ours, for instance:

1. Air resistance? What air resistance?

From the moment you launch your wingless bird into the air, it follows a majestic, perfect parabolic trajectory, nothing like your disappointing attempt to scoring a paper bin 3-point shot using your scrunched up artistic impression of a winged tiger spewing rainbows.

2. Casually laying an egg in mid-air makes you go faster

The white bird is one that seems to deny so many laws of physics that it would undoubtedly deny climate change as well. Sure force does equal mass times acceleration, but losing half its mass doesn’t halve the gravitational acceleration – it’s a constant, so white bird should surely continue to follow the same, air-resistance-defying trajectory.

3. Action < REACTION!!!!!!!!!!!!

Every action has an opposite reaction, so assuming that white bird is twice the mass of the egg, then the bird should only experience half the acceleration of the egg. Out of all the birds, except for green bird, who somehow turns into a bird boomerang, white bird is the one most like that person who didn’t finish high school but created a consumer electronics company and completely reinvented computers. White bird is the Steve Jobs of Angry Birds – reinventing physics to distract us from the fact that everyone can smell that one guy’s casserole on the train home.

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There will be a total lunar eclipse next Tuesday evening (15 April). The already-eclipsed moon will rise in the east at 5:30pm, weather permitting. This is a good year for lunar eclipses. There will be another one, even better than the first, on the night of Wed 8 October.

lunar.jpg-large

To sweeten the deal, Mars is also at it's closest and therefore relatively large and bright in the night sky. After you've had a look at the Moon, once it has finished it's eclipse, then had your fill with Mars, look back down to the horizon a little bit to see Saturn rising. With even a small telescope (Mine is a 5.25 inch Dobsonian) or a pair of binoculars you should be able to see some features of Saturn.

A couple of weeks later there is a partial solar eclipse in the afternoon of Tuesday 29 April - low in the west, just before sunset. It starts at 4.14pm and the Sun sets at 5.15 with half the Sun's diameter covered. For more, see this fact sheet from the Australian Astronomical Society.

Click here for more info

If the weather isn't on our side, you can view the live webcast from space.com

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There will be a total lunar eclipse next Tuesday evening (15 April). The already-eclipsed moon will rise in the east at 5:30pm, weather permitting. This is a good year for lunar eclipses. There will be another one, even better than the first, on the night of Wed 8 October.

lunar.jpg-large

To sweeten the deal, Mars is also at it's closest and therefore relatively large and bright in the night sky. After you've had a look at the Moon, once it has finished it's eclipse, then had your fill with Mars, look back down to the horizon a little bit to see Saturn rising. With even a small telescope (Mine is a 5.25 inch Dobsonian) or a pair of binoculars you should be able to see some features of Saturn.

A couple of weeks later there is a partial solar eclipse in the afternoon of Tuesday 29 April - low in the west, just before sunset. It starts at 4.14pm and the Sun sets at 5.15 with half the Sun's diameter covered. For more, see this fact sheet from the Australian Astronomical Society.

Click here for more info

If the weather isn't on our side, you can view the live webcast from space.com

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Written by Jonathon Leonard

A group of scientists in France have approached the problem of the age of the moon at a whole different angle and have totally changed our previous estimates of its age. The study was published in the prestigious journal Nature​ and has received a fair bit of media attention. They team used computer simulation to re-estimate the timing of the huge celestial collision between Earth and a Mars sized body that created the moon.

Giant impact, Credit: Wikipedia Before we get into the details of the study, let's first have some background information.

At some stage after the formation of the solar system (called the condensation of solids), there was a huge collision with Earth by a body similar to the size of Mars. This collision significantly changed the structure of Earth's mantle and core as well as causing the formation of the moon by a large chunk flying off post-collision.

Before this study, all attempts to date this huge collision were done using dating from radioactive elements. Much of these dates of collision were between 30 and 50 million years after condensation of solids in the solar system (that is, the formation of the solar system). However, this team of scientists took an entirely different approach to dating the moon-forming impact. They used a series of computer simulations that predicted the formation of the solar system.

The computer simulations initially used classical ideas on the early solar system, such as similar orbits of the planets as they have today and a large area of matter around the sun that contained all the building blocks of the solar system. However they found this simulation had problems. For example, the sizes of Mars were all wrong.

Instead the scientists changed the initial conditions so that the disk of matter around the sun that contained the building blocks of the universe was much smaller. After a few adjustments, they achieved simulations of our solar system similar to our current system.

Yet even after making these successful simulations, there were still a range of viable simulations that predicted a moon forming collision at a wide range of dates. So which predictions are more likely to be right? Well to do this, the group of scientists measured the abundance of a group of elements in the mantle that are high siderophile (which means easily dissolve into iron). During the huge moon-forming impact, these elements should pretty much all have sunk into the mantle since they dissolve into iron so easily. Thus the presence of highly siderophile elements (HSEs) that aren't in the core must be from after the impact, called late accreted mass. By comparing the amount of HSEs in the mantle to those we find in meteorites that have a similar composition to the early Earth, we can take a good guess at how much late accreted mass the Earth has gained.

Now comes the fun part. The scientists compared the late accreted mass measured on Earth to the values predicted in the simulations. The values where the simulations consistently agree with our measured values (within an acceptable uncertainty) was between 67 and 126 million years after the formation of the solar system. In fact, out of the large number of different simulations, not one had the correct late accreted mass that had an impact earlier than 48 million years after the formation of the solar system. The scientists estimated that there is only a 0.1% chance that the big impact occurred before 40 million years after condensation, a huge result considering this was smack bang in the middle of many previous predictions.

So what does this result mean?

Well firstly, it means that the moon formed much later than we previously expected. It also means that the disk of matter that revolved around the early sun and contained all the building blocks of the planets has a much smaller area than previous thought. Finally the wrong radio dating figures could mean that these figures may have come from elements before the collision, meaning that the moon-forming impact didn't totally reset the mantle as previously thought.

Perhaps the biggest lesson from this study should be that to solve a problem in science, it is often useful to look at it from a completely different perspective. This is where Einstein achieved much of his genius (look up the Equivalence Principle from General Relativity for example). Those successful in science (and life!) aren't necessarily the most intelligent, but the most creative and willing to look outside the box for a solution.

Read the full article here: http://www.nature.com/nature/journal/v508/n7494/pdf/nature13172.pdf

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Written by Jiro Funamoto

The universe is huge, and we're tiny!

The space shuttle. Credit: NASA

Our lives are ~80 years. On the other hand light takes 45 billion years to get from one side of our visible universe to the other. So it's commonly thought that there's no way living humans could really travel away from the Earth further than some invisible sphere of perhaps 80 light years (given that we can travel at the speed of light, and we put a newborn baby on a spaceship).

Since the speed of light is finite it therefore seems like such a restriction on how far living humans can venture into space, since at most we can only go almost as fast as light.

This is a misconception.

Time dilation (or equivalently length contraction) means that as long as the spaceship is travelling close enough to the speed of light, you can get to the edge of the universe in your lifetime. In fact, you can get to the edge of the universe in 2 sec (of your life) if you were going close enough to the speed of light. If you had a spaceship that could really approach the speed of light, you can travel to any destination in any amount of time you wanted.

Unfortunately, when you get there, the outside world might be 45 billion years older than what you felt was 2 secs ago.

Mind blown yet?

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"Most people have questions about the universe, but don't know where my office is, so I have come here." – Professor Geraint Lewis

A guerrilla science experiment was successfully undertaken last week on Eastern Avenue at the University of Sydney when Professor Geraint Lewis from the School of Physics t the Ask A Cosmologist stand on the University Market day.

ask-cosm.jpg

Similar guerrilla science activities have taken place in other places and we wanted to see if it was an option here. The conclusion is that the idea was most definitely a success and worth a repeat. Over the 2 hours we answered questions raging all over science and Physics (and further afield!) from about 15 eager and interested people.

"I declare guerrilla sciencing a success. We were asked about expanding universe, big bang, cannibalism, Dark Matter and Energy BICEP2, and other things. Yes, will we be back!" exclaimed Professor Lewis

Professor Geraint Lewis works on Dark energy, gravitational lensing and galactic Cannibalism. He has some recent results that we have highlighted at the School of Physics, you can read more about his latest results in the Latest News page from the School of Physics.

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Written by Jacob Henegan

Black Holes are some of the most perplexing things in the universe. A single point of such extreme mass that nothing, not even light, can escape. When they were first predicted by General Relativity, scientists assumed they were just a fluke in the maths, but now not only do we know that they exist, but they are so common that astrophysicists believe there to be over 100 million in our galaxy alone.

Black hole. Image Credit: www.scienceblogs width=

But since they give off no light, we can't actually see black holes, so how do astronomers find them?

Since black holes are 'black', and give out no light, astronomers can't observe them directly, they have to look not at them, but on their effects on the universe. There are 3 common ways to do this

1. Orbits

Some black holes, such as Sagittarius alpha, the supermassive black hole in the centre of our galaxy, can be observed by the the stars orbiting them. Based on the speed and distance these stars orbit from, physicists can calculate its mass and location to a pretty high level of accuracy.

This technique is a really safe and accurate way of inferring black holes, but we need to have a lot of information about the surrounding region so it only works for nearby sources like those in our galaxy.

2. Gravitational Lensing

Einstein's theory of General Relativity tells us that objects with mass bend the fabric of spacetime itself, bending the path of light. Now, it takes a LOT of mass to make this a noticeable effect, but with supermassive black holes weighing in the order of 10^37kg, more than a million times the mass of our sun, the distortions are pretty big.

This causes an effect called gravitational lensing, where objects we would normally see as points, like stars, or distant galaxies, appear instead like streaks of light. The blackhole actually warps the ray of light as its moving towards us, and that's how we see it.

This technique, again, doesn't work for every black hole, it only works for Supermassive black holes, not the more common stellar mass black holes which are only a few to a few dozen times the mass of the sun, and we can only make good calculations from the effect if the black hole moves past the background, so we can compare them.

3. Accretion Disc radiation

The most common method of detecting blackholes, however, is by looking at the stuff falling into them. When stuff – whether its dust, asteroids, planets or stars, falls into a black hole, it usually doesnt fall straight in, but comes in at an angle. When this happens, the massive tidal forces from the black hole rip objects apart into dust particles, which then begin orbiting the black hole. The dust particles from everything falling into a black hole will form a disc, usually called an accretion disc. These discs are so dense and the particles are moving so fast that the friction between dust particles causes them to heat up to immense heats.

You know when metal gets really hot, it glows red or orange? And if you make something way, way hotter than that it can glow blue or white? Well these dust particles, just because of friction, are so hot, that they skip the visible spectrum altogether, and glow in X-rays! (good spot to throw in an EM spectrum animation)

By looking at the source of the light with an X-ray telescope, we can work out from the spectrum and brightness of the source whether it's a black hole and roughly how massive it is.

This technique works for black holes of all mass-ranges, but requires other matter to interact with the black hole and form a disc.

Gravitational lensing. Image Credit news.discovery.com

With these techniques, we can still only observe a tiny, tiny fraction of the billions of billions of black holes astrophysicists believe there to be in the observable universe, and there's still a whole lot we don't know about them, but as more techniques get developed and the technology improves, we're sure to learn a whole lot more about this big crazy universe we live in

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Written by Aina Musaeva while on one of her Observing trips

Right now (late April to early may 2013) the night sky contains many beautiful stellar objects to look at with a telescope and naked eye. Gorgeous summer objects are still visible in the low western sky early in the evening with many winter ones just rising in the east later at night.

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The SKA

24 Apr

Written by Jason Drury

Currently under development, the SKA or Square Kilometre Array, will be the world's largest radio-interferometry based telescope, with its antennas having an effective collecting area of approximately one square kilometer.

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Written by Ben Pope

A discussion of light, black holes and Gravity all leading up to a central discussion of why is it possible that light can get trapped in the gravitational pull of a black hole is light is supposed to be massless.

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The Michelson Interferometer: The main component of the Michelson-Morley Experiment

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