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Space, the universe and everything


Space, the universe and everything

Is there anybody out there? (Source: ESA/C. Carreau)

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How the universe began

Whenever I look up at the sky at night and see the Milky Way I often wonder about the Big Bang. What I can't get my head around is how the process could go from nothing to the start of the Big Bang. How can one have nothing and then suddenly all the necessary materials that produced our universe? What alternatives are there for the big bang theory? I don't believe in creationism but cant get my head around all space, time and matter coming into being from a single point?
—Cameron McShane and Paul Littlely

The reason people have problems understanding the Big Bang, is that they are imagining that space and time have always existed, like a picture frame ready for some painter to come along. They are trying to see the big bang "happening" within that frame. They are pretending that time stretches infinitely far back and that the big bang happened like a bomb going off.

In order to make any progress with understanding the origin of the universe (at least as much about the origin of the universe as we can squeeze out of cosmological observations and general relativity) we have to get rid of this eternal space and time idea. One simple way to remind ourself of this is the phrase: There was no time before time came into existence.

The big bang theory is a little like Darwiniam evolution. It is a theory which has been so successful that all competitors have been marginalised. So there really are no good alternatives. However, there are important pieces missing that aren't understood very well at all...and these are arguably the most important pieces. How did life begin? How did the universe begin?

Conservative versions of the "big bang theory" don't even discuss the origin of the universe...many scientists are content to discuss the big bang only so far as the observational evidence goes...and it goes back surprisingly far. But, as is always the case, it becomes more tenuous as we go further back. For example, we can study the production of helium in the universe during the first three minutes and we can test our predictions quite precisely. We can study the formation of the first atoms about 400,000 years after the big bang. To some extent we can even test theories about what happened after the first billionth of a billionth of a second. Our ideas about what happened earlier (or even whether it makes sense to talk about times earlier than that) should be approached with a healthy scepticism.

If you could find good evidence that some star or galaxy (or anything else) was older than the 13.7 billion year estimate for the age of the universe, you would have strong evidence against the big bang and you'd win a Nobel prize and alternatives to the big bang would be popping out everywhere.

— Dr Charley Lineweaver, Associate Professor, ANU

Several years ago Paul Davies and Phillip Adams did a series called 'The Big Questions', followed by More Big Questions. See the section entitled 'In the beginning' - for a detailed discussion about the beginnings of the universe.

ABC Science Online

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Zero-gravity birth

Are there any predictions of what will happen when people are born in zero or weaker gravity conditions eg will they be able to live on Earth after several years in such conditions.
— Susan Robinson

Astronauts used to have large difficulties readjusting to earth's gravity after long duration space flights (imagine watching TV for a few weeks from a very soft couch and then trying to get up and walk around - you'd have difficulties too).

The best solution to these difficulties appears to be regular focused exercises that put stresses on bones and muscles in the way that earth's gravity does. This is what astronauts now do. I imagine that if a human or any other biped or quadruped was born in zero gravity and lived in it for a large fraction of its formative years without such focused exercise, some degree of walking impairment might be irreversible.

— Dr Charley Lineweaver, Associate Professor, ANU

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Is gravity faster than light?

Light travels at a finite speed (but nothing can travel faster than it). It takes light approximately eight minutes to travel from our Sun to Earth (1AU). But if the Sun were to disappear the gravitational effects would be felt instantly. Is all this true? If so does gravity travel faster than light?
—Josh Paul

No, gravity does not travel faster than light. The gravitational force also travels at the speed of light. This was postulated by Einstein, and was first measured in 2003 by scientists at National Radio Astronomy Observatory in Charlottesville, Virginia. Formally the effects of gravity are manifested through its effect on the shape of space-time, and this distortion moves at the speed of light. So if the Sun were to suddenly disappear then space-time would react to that at the speed of light and in about 8 minutes the Earth would head off in a straight line, along a tangent to its orbit at the time that the gravitational force from the Sun disappeared - ie about 8 mins after the Sun itself disappeared, and at the same time that things suddenly got very dark!

—Prof John Lattanzio, Director, Centre for Stellar and Planetary Astrophysics, Monash University

Gravitational influences also propagate at the speed of light. According to General Relativity, changes in distributions of mass produce gravity waves, which communicate the changes. There is currently a concerted effort to try to detect these waves experimentally.

Basically, if the Sun were to disappear, we would only know about it eight minutes later.

— Dr Mike Wheatland, School of Physics, University of Sydney

Although gravitational waves have not yet been observed, we think that such a change in gravitation fields will travel in much the same way as light or other electromagnetic waves travel, and with the same speed. Thus it would be about eight minutes before we knew that the Sun's gravitational field has disappeared.

— Prof Peter Dyson, Department of Physics, La Trobe University

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What the universe looks like now

If the light from stars and galaxies that we see (telescopes, Hubble or eyes) is from millions of years ago, what does the universe actually look like now and do we have any way of telling what that is?
— Ruth Watson

This is a good question. It raises a subtle issue that we do not have to deal with on a daily basis, because of the speed of light being so fast. This is the issue of "simultaneity". How do two different people know that two events occurred *simultaneously*? Einstein told us that there is no preferred time, only time relative to an observer. So when the question asks "what does it look like now" we have to reply "according to who?" The concept of "now" is fuzzy!

It is true that when we look in the sky we see the stars etc as they were when the light left. This is also true when we look at our watch. We see the time when the light left the watch, not the time "now". But since these are so close together, we do not even consider that the times are different. But technically they are. And when you start dealing with huge distances, then it can be important.

So imagine looking at the binary star system alpha Centauri. It is about 4 light years away so we see the two stars as they were 4 years ago. How do they look now? Well - they look exactly as we see them! It depends on who is looking and how far away they are... Maybe we should ask "How are the stars arranged now?" Well, if you know the orbit, you can move them forward 4 years, and that is the position they have "now". But its almost meaningless, as you cannot see them in that position. Further, maybe some disaster occurred and the system has been destroyed! We simply do not know until the information (ie light in this case) gets to us. So what do we mean by "real position" and "now"? Until the information arrives, we simply cannot be sure!


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Lunar lifestyle

We are told Man is going back to the Moon and beyond, but has anyone yet thought of providing him with safe functional living quarters below ground? A thin walled space vehicle above ground will not protect Mankind from solar flares etc.
— Maxwell John Bancroft

The surface of the Moon and Mars is largely blanketed by regolith, which is loose material like soil, sand, and gravel that can be easily excavated. There has been quite a lot of study into using Lunar and Martian regolith to provide radiation shielding. The advantage of this is that you can use local materials to construct the radiation shielding needed for long missions.

There are several ways that regolith could be used. The simplest is to bag it and drape the upper surfaces of your lunar or Martian station with these bags. Or you could erect a flat roof and spread a layer of regolith on this. Other suggestions include burying the entire Moon or Mars station by piling regolith over the top or digging a trench and placing your living modules in these before roofing these over and burying them in more regolith.

It might even be possible to use natural caves, such as lava tubes, as shelters, if these are in the right places and the right size and shape. Lava tubes, rather like those found in Queensland and Victoria, are believed to occur in several places on the Moon and Mars. As for using places like Coober Pedy as a way of learning how people might cope with living underground, I think this is an excellent idea.

— Dr Jonathan Clarke, Vice President, Mars Society Australia

What we can expect to see is the construction of bases using modules like those on the International Space Station. Radiation shielding will have to be improved. Coping with dusty places like the Moon and Mars will have its own challenges. Hazards may have to be diminished by limiting the duration of occupation. Not only the major space agencies but also the MARS Society is actively experimenting with such habitats and lifestyles, including here in Australia.

— Prof Malcolm Walter, Director, Australian Centre for Astrobiology, Macquarie University, Sydney

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Moons with moons

Why don't moons have moons?
—Paul Gardiner and Craig Sutton

The Earth orbits the Sun, and so is a satellite of the Sun. The Moon orbits the Earth, and so is a satellite of a satellite. Even small asteroids orbiting the Sun can have other asteroids orbiting them (asteroid-moons). So, in theory, our Moon, or the moon of any other planet, could have its own moon: a moon-moon.

The orbit of such a moon-moon must lie within a certain restricted region around the primary moon, called the "Hill sphere". The size of the Hill sphere depends on the gravitational fields of all bodies in the system. Massive bodies (like Jupiter and Neptune) that are far from other massive objects will have the largest Hill spheres, and thus the largest regions in which stray objects could be "captured" into orbits to become moons.

Most moons are so small and orbit so close to their parent bodies that they have very small Hill spheres and thus very small regions in which moon-moons could exist. Even within this region, a moon-moon may not be long-lived. Tidal effects may distort the shape of the primary body, changing the gravitational force on the satellite and slowing it down or speeding it up. In many cases the satellite's orbit will decay: the moon-moon will either crash into its parent moon or be torn apart by tidal effects. Indeed, after an extremely long period of time, some of the moons in the Solar System are expected to crash into their parent planets. Perhaps one distant day a curious person will ask, "Why don't some planets have moons?"

— Prof Penny Sackett, Director, Research School of Astronomy and Astrophysics, ANU

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The Outerverse

If the universe is infinite and at the same time expanding, what is outside of our expanding universe? Is it finite or infinite?
— Edan

The latest cosmological observations are consistent with the idea that the universe is spatially infinite (but the portion of it that we can see - the observable universe - is finite). The universe does not expand like a bomb into previously empty space. Astronomers casually say that distant galaxies are "receding" or "moving away" from us, but the galaxies are not travelling through space away from us. They are not fragments of a big bang bomb that blew up 14 billion years ago in a specific place.

Instead the space between the galaxies and us is expanding and the big bang happened everywhere 14 billion years ago. One way to imagine this is to consider an infinite rubber sheet. Draw a circle on the sheet to represent our observable universe. Draw lots of other circles anywhere you want on the sheet to represent other observable universes - they can overlap with our circle if you like. Now let the rubber sheet expand. All the circles will get bigger but they don't expand into previously empty space - all of space is expanding and this expansion does not require empty space on the outside (wherever that is) to expand into. When it expands, it does not claim previously unoccupied space from its surroundings. In Einstein's general theory of relativity, the foundation of modern cosmology, space can expand in this way as well as shrink and curve without being embedded in a higher-dimensional space.

— Dr Charley Lineweaver, Associate Professor, ANU

When we observe the Universe we find that it looks pretty much the same in all directions. We call this isotropy. Maps have been made of where galaxies reside in the nearby Universe, and these show that the Earth is not at the centre of the Universe. The Universe must therefore be isotropic around all points (ie homogeneous).

When these observed requirements of isotropy and homogeneity are put into the theory of General Relativity, a solution is found where space can expand (or contract). However this space is not thought of as expanding into something. In General Relativity space and time cannot be thought of separately as we do in everyday life. Rather space and time make up a 4-dimensional "space-time". Since its very hard to think in 4 dimensions we can consider the following simple analogy.

Take a balloon, and think of its surface as a two dimensional world (in analogy to our 3-d world). Things can move along the surface but not perpendicular to it. To an observer on the surface this world looks isotropic around every point, just like our universe. If the balloon is blown up, then the surface expands around all points, again just like our Universe. In this analogy the balloon is not expanding into space, but rather it is expanding in time. The balloon analogy represents a finite universe (since one can measure the area of the balloon). However General Relativity permits universes that are infinite as well. We believe our Universe is infinite in extent.

—Dr Stuart Wyithe, Department of Physics, University of Melbourne

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Why doesn't the Earth 'capture' asteroids?

I read today about the impending near miss with the meteor/asteroid. Why doesn't the Earth's gravitational field capture these near miss satellites and why don't we have thousands of them orbiting the Earth? If the answer to my first question is that the orbits would decay and fall into the atmosphere to burn up, then why doesn't the Moon's orbit decay?
—Craig Suttonand Mark

Whether or not a passing body can be captured into the Hill sphere (the gravitational sphere of influence around an astronomical body) depends on how fast it is travelling. Many fast-moving objects will be able to escape, although their trajectory may be altered by the "close" passage.

Our own Moon's orbit is actually expanding, not decaying. This is because the Earth rotates faster than the Moon orbits the Earth, so that the tides that the Moon raises on the Earth "lead" or are slightly "ahead of" the Moon, speeding it up. This allows the Moon to move to a larger orbit.


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Is there anybody out there?

What is the chance of there being life and then intelligent life in our galaxy or the whole Universe?

As our knowledge about types and numbers of planets in the galaxy improves, the answer to this question is becoming more and more dependent on philosophy (how does one define "intelligent"?) and on our knowledge of biology (under what conditions can life thrive?) than on our knowledge of other planetary systems.

What we do know is that at least a few percent of all stars like our own Sun have planets. Some of these planets are larger than Jupiter and made of gas. Others are a few times the mass of the Earth, and probably rocky or icy worlds. Astronomers doubt that any of the 194 planets now known orbiting other stars are likely to support liquid water at their surface. Liquid water is sometimes taken to be a condition for "life as we know it." (Of course, it is quite possible that nature includes "life as we don't know it"!)

Planets similar to our Earth are difficult to detect, and we have only just begun to search with adequate tools. Within the next five to 20 years, we should have a good estimate of the fraction of normal stars with vaguely Earth-like planets. Given the huge number of stars in our galaxy (tens of billions) and the similar number of galaxies in the Universe, we can probably be certain that a large number, perhaps billions, of other Earth-like planets exist somewhere in the cosmos. The question, for biologists and philosophers, is then: "Could any of these planets harbour intelligent life?" In the absence of evidence to the contrary, safe money may be on "yes."


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When the Sun dies

Assuming that the reaction that makes the Sun work was to stop, how long would it take to cool down and what would be left?
— Alan

The Sun is powered by the fusion of hydrogen. If this were to suddenly stop, then the Sun would contract on itself, just as it did earlier in its life, when it contracted from a large gas cloud to a star. It was only the start of hydrogen fusion that halted this contraction, and if we somehow turn off the fusion then the contraction will continue.

This contraction will release gravitational energy and there would be no noticeable change in the brightness of the Sun for quite some time - something like a few million years! But it would gradually change, and as it contracts it uses up the gravitational energy available to it, and it would eventually dim and disappear, after maybe 50 million years, as a faint ball of gas not unlike a very massive brown dwarf.


Due to the extreme pressures and temperatures at its core, the Sun can fuse hydrogen into helium and other elements, releasing energy. The extreme conditions are due to the outer layers of the Sun squeezing the core and making fusion possible. Strangely, if we turned off nuclear fusion, the temperature of the core would increase. The radiation produced by fusion pushes on the outer layers and acts to reduce the central pressure - without the radiation, the core would be squeezed to higher temperatures (this was one of the original ideas for how the Sun was powered).

The Sun would continue to glow brightly for tens of millions of years before reaching the limit of its contraction, and then, as a big ball of hydrogen and helium, would cool down towards absolute zero over billions of years.

— Associate Professor Geraint Lewis, School of Physics, University of Sydney

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Space colonies

How close are we to realising the dream of humankind travelling to other worlds and solar systems, perhaps even colonising them. Also, what are the most likely means of interstellar travel and humans actually surviving the many hazards it will probably involve, such as massive acceleration forces or high-velocity particles?
— Cricket

Travelling beyond the solar system is an old and fabulous human dream. The technological advances needed to achieve this are immense, and I suspect it will require several centuries of advances in almost every field of human endeavour before we can do this, if it is possible at all.

An important first step towards seeing whether we can actually achieve this is the exploration and settlement of our immediate space environment, starting in Earth orbit and moving on to the Moon, and Mars. It will be on Mars, the most hospitable world in our solar systems for human life, that we can answer the question as to whether or not humanity can become a multi-planet species, or whether we must be content with living on Earth. We don't know if it will be possible to live off our planet, but I believe it is important that we try.

— Dr Jonathan Clarke, Vice President, Mars Society Australia

Acceleration is not a problem as it can be done gradually. I'm told that the launch of a NASA shuttle is not uncomfortable for the astronauts. Dangerous radiation, bone loss and muscle deterioration in space are the main problems. In time, all these problems will probably be overcome. Then the major problem for long-term travel will probably be psychological health.

During this century we can expect to see exploration bases established on the Moon and Mars, comparable with those already existing in Antarctica. Just possibly astronauts might venture even further afield within the Solar System. But the stars will remain unreachable.



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Published 13 July 2006

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