Q & A

Hello.Since the universe is exspanding is it possible that some gallaxies eventually may merge as a result or is there a force that will keep them apart forever.

Wuggy - USA

It depends on how close they are now. Take the Milky Way for example; most of the galaxies we see will be carried away from us by the cosmic expansion and we will never merge with
them. However, our near neighbours are close enough that the gravitational
attraction between us can overcome the expansion.

We're expected to merge with the nearest big galaxy, the Andromeda Galaxy, in a few billion years
time. It should be a spectacular collision - perhaps from the outside it'll look something like those shown on this web link: http://tinyurl.com/ypjzp5

Chris Lintott

First, my congratulations to you for this great description of a very difficult subject in a very simple language. Full marks for this!

Then, to my question: I am very perplexed about "seeing back in history". If we can see an object 'X' 10 million years in history (i.e. at 10 million light years distance), then how come we get here
earlier than light. When I mark 2 points on a deflated balloon and then inflate it, these 2 points move away from each other but the problem starts here. If they are undergoing changes, like primordial galaxies, they both will change as they move away. So, if point A is changing from gaseous to solid state, point B is also having same change, albeit with some difference in rate of change. However, by the time they are very far from each other, both will have undergone
considerable change and it should not be that A is far advanced and B is still primordial. If I am correct then when seen from A, B should not look vastly underdeveloped.

Our Milky Way galaxy and some other remote galaxy at 10 billion light years started developing round about same time and were initially close together. Then we moved apart and during this kept on developing. So we should not be seeing it in a juvenile state. Can you guide me how this is possible?

Kamran Faruqi - Pakistan

LOOKING BACK IN TIME .... perhaps this is a good way to start the New Year !

Well, thanks for an interesting question, Kamran, and very well expressed -- although I do suspect that the fact that you are asking indicates that we were not quite good enough in our explanations in BANG !

You are right in saying that points A and B on your 'balloon' are both changing and evolving. If we could sit in a position where we could see both of them at the same time, say, half way between them, we would undoubtedly be able to confirm this .... because we would be seeing light which started its journey towards us at about the same time in each case.

But suppose we now shift our vantage point ...we are now sitting at point A. We can make a good guess that Galaxy B is actually in a similar state of development as our own ... but we cannot confirm this by observation. We can only draw conclusions from what we can see. What we see, when we look towards B, is light that left B a long time ago. Light seems to travel instantaneously to us, so we never question 'simultaneity' in our every-day existence. The fact that we might be trying to check the time from a clock which is a mile away would not bother us ... we would not be thinking ... "This light left the clock some time ago, so we must make adjustments." But on a cosmic scale, this is exactly what we must do. The light we see coming from our Sun left it about four minutes ago, so in theory, at any moment, it MIGHT have blown up, and we would not discover the fact until four minutes later. But the light from Galaxy B left it millions of years ago. So, logically, what we are seeing is an image of that galaxy which is millions of years out of date. Yes, it may be highly evolved at the moment we choose to observe it, but we will see it as it was in a bygone age. There is no asymmetry here ... the same thing exactly happens the other way round. People on galaxy B will see US (assuming we are in Galaxy A!) as we were millions of years ago ... even though they will guess that our galaxy is highly evolved like theirs ...

I wonder if this makes things any clearer ... It's strange. It seems to me, Science actually sometimes asks the same things of its adherents as religion ! Scientists really ask us to BELIEVE that certain things happen ... and they do not tell us why. I find a lot of the concepts in Einstein's relativity are really not as difficult to understand as people make out. A child could understand that, for instance, if we measure the length of a ruler as it moves faster and faster relative to us, the ruler might get shorter (which is what Einstein predicts). But the problem is believing this is true - because we don't experience it in every-day life. The reason we do not experience such things is that we don't rush around at speeds anything like the speed of light (186,000 miles per second). If we did, then I'm sure we would have no problem with Einstein's 'theories' - they would just be what we see every day. In the limited amount of teaching I have done, I have actually found confirmation of my 'theory'. Kids of school age actually DO find it easier to 'believe' Einstein's theories ... easier than grown-ups who have had more time to get into set ways of thinking. It's not that the kids are more intelligent than the grown-ups (thought this may be so!) - their minds are just more flexible .. more open. So, to get to grips with Cosmology, perhaps the best thing we can do is just forget all our preconceptions .... suspend our disbelief, like watching a Superman film, and ... enjoy the ride !!

I hope this is helpful ! All the very best to all you cosmologists out there ....

Dr. Bri

Brian May

Is any part of the interplanetary dust that creates the Zodiacal Light in earth orbit? Does the earth have a vestigial ring system of some form? Could the earth capture some of the interplanetary dust and hold it in some structure similar to a ring? Is the spectrum from the dust identical to the solar spectrum or is it possible to determine the chemical elements in the dust based on a unique spectral pattern?

Stan

Questions are bang-on target.

It's a very fair question as to whether there is any dust in orbit around the Earth. And it's discussed in some detail in my thesis .. I will have to get it out there soon, so people can see. A "Cis-Terrestrial Cloud" has been certainly been proposed as a source of Zodiacal Light, as early as the 1850's. One of the advantages of our research, which is the only kind of observation which maps velocities in the cloud, is that it ought to be able to distinguish between such a Geocentric cloud and circum-solar orbiting dust.

To cut a long story short, my own conclusion, based on our Doppler measurements, was that if there is a contribution from Dust in orbit around the Earth, it is small. There are other considerations, though, as you'll see in my historical review in my thesis ... OK ... better send you a copy! The IRAS infrared satellite experiment and its successors, COBE, etc, found evidence of a resonant ring of dust, scattered along the Earth's orbit, and it seems that there is a concentration, (or, to use the technical term "blob"!) lagging behind the Earth. So the story is definitely not simple!

As to the other question ... the spectrum of the ZL in the visible is just that of reflected sunlight - but shifted in various degrees by the Doppler effect ... luckily for me. However ... in the infrared, we see an emission spectrum from this dust, because it's warmed by sunlight, and it behaves like a black-body emitter, but apparently with a feature or two superimposed upon it, attributed to transitions between vibration energy levels in the crystals of some of the material in the dust. And, yes, good thinking ... attempts have been made to identify the composition of the dust from this spectral information. (silicates are the favourite suspects in this case .

Finally .... a big 'hmmm ..'! Yes, the scientific truth as it's being revealed every day in 2007 is definitely stranger and more wonderful than (most) fiction!

Cheers!

Brian May

CME & Comets Tail Query --- I bought BANG and I watch The Sky at Night and even though I do not understand what is going on out there the subject fascinates me, I think it should be simple but it isn't and where my amateurishness shows through is on my initial thoughts on looking at the image. i.e. If light has no mass what was it that bent and tore off the tail.?

I know I am going to feel silly for asking this but if you don't ask you will never truly learn.

Al the best to you

Gordon Jennings

Gordon Jennings, UK

A very sensible question, actually, Gordon. Yes, you're completely right about light having no mass. Strangely enough, though, it seems that light can still get deflected by gravity, or perhaps 'appear to be deflected' might be a more appropriate description - since according to Einstein, in his brilliant General Relativity theory, it is SPACE that is distorted by gravity, and light is still taking the shortest path.

HOWEVER !!! This has nothing at all to do with the tail of this unfortunate comet ! The tail is made of gas and dust, which simply reflects light, the same as any other object ... it's a bit like a cloud of smoke on earth, for instance. So when the high-speed material material ejected from the Sun hits it, the tail matter gets swept away, just as our cloud of smoke would ... even more so, since there is no air around it to slow it down out there in space. It's pretty spectacular, isn't it ?! I love these things which turn up and have not been predicted. Once we have seen this, it's easy to come up with reasons why it happens ... but until this series of pictures was taken, to the best of my knowledge, nobody had ever predicted this phenomenon.

I love Astrophysics !!!

Cheers !

Brian May

First of all, congratulations for the thesis and I wish you all the best for August 23rd! And of course, thank you for the beautiful music. I was discussing these topics some days ago, with a friend. What do you think about them?

1. If the second law of thermodynamics establishes that Entropy (measure of disorder) always increases… why, from the chaotic state of post-Big Bang, this universe --more complex and organized-- was built?

2. And, If the universe was created as a result of the Big Bang, why all the galaxies don’t move away from a single common point (where the explosion occurred), but they get farther away from each other as if the space between them grew?

Mariana de Giuli - Buenos Aires, Argentina.

1. Well, the entropy of that (theoretical) tiny embyo universe was actually very low. You see, entropy, or order, is partly defined by how confined (or defined) in space everything is. It's like if you swept up all the dust in your room and confined it to a small dustpan. You would have decreased the entropy of the dust. But the second law of Thermodynamics would still apply, because you would have dissipated so much energy (in heat and noise, etc) in doing the job.

As the Universe expands, the matter in it becomes more and more spread out, so, overall, its entropy is increasing. Stephen Hawking has discussed the consequences of the possibility of us being in a collapsing universe. In this situation, entropy ought to decrease with time. But since we seem to measure the direction of the arrow of time by Entropy anyway, presumably time would be running backwards, and so we would not know !!! Intriguing ideas.

2. The second part of your question is a little harder to visualise. I recommend our BANG! book for a full explanation. But the analogy of ink spots on an expanding balloon has often been used to give an idea of what is going on. On the two-dimensional surface of the balloon (analogous to the 3-dimensional universe we live in), as we blow up the balloon, the spots move away from each other. But there is no 'centre' to their motion ... an ant could walk all around that balloon surface, measuring the rate at which the spots were moving apart. He would never come to a boundary, and he would never find a centre. But all the spots would be moving apart at the same rate.

The reason there is no 'special' place or centre, is because ALL points in our universe AND ALL THE SPACE THEY EXIST IN were in that tiny embryonic speck. Space did not exist outside the primeval 'atom'. So it is not a question of stuff expanding into an already existing space. Like the surface of our balloon, it pretty much did not exist before the expansion. I hope this helps !!!

cheers

Brian May

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