Obviously my title is tounge-in-cheek. Many people have to work hard to turn theories into truths. However, here are some things that get talked about a lot as fact, but really are just good theories. When verified by direct observation, most of these will be considered a nobel-prize winning, ground-breaking new frontier in physics. Until then, they are just good ideas, waiting to be verified.

Dark Matter & Dark Energy - [Read More about Dark Matter and Dark Energy]

Dark matter is hypothetical matter that feels no effect from electromagnetism, so we cannot see it. Its presence can only be inferred by the gravitational influence it exerts. Galaxies do not rotate as expected by Newtonian dynamics. The Coma cluster of galaxies also has properties that gravity cannot explain.

Dark energy is similarly mysterious, but even less easy to understand. It is a kind of energy that permeates the whole universe, driving it apart and causing it to expand. These two things together purportedly make up 96% of the content of the Universe.

Physical cosmologists study dark matter and dark energy with great interest. Change their names to ‘gravity not doing it what it should’ and things can look slightly different. A branch of physics labelled MOND (MOdified Newtonian Dynamics) tries to explain the observational evidence without adding in unknown forms of matter and energy. There are also many scientists who feel that ‘dark energy’ gives the wrong impression and that this stuff might be normal matter that we simply don’t see for some reason.

So either gravity is wrong or matter is. That is quite a dilemma for astrophysicists to resolve.

Gravitational Waves - [Read More about Gravitational Waves]

Now, I’ve gotten in trouble before for having a beef with gravitational waves, so I’ll try to be kinder here. Gravitational waves are fluctuations in the curvature of spacetime which transmit the energy of gravity and propagate its effects through the universe. Light’s energy is transmitted to us by fluctuations in the electromagnetic field, this would be an alternative spectrum of waves, detectable by completely different means.

The study of gravitational waves has received a nobel prize (1993, I think?) when they were indirectly detected in a binary system containing a pulsar. The orbital energy in the binary system was seen to decay in exact accordance with the theories of gravitational wave physics.

Einstein’s general relativity explains gravitational waves very well  - in fact if gravitational waves don’t exist there is a big problem. The problem comes along when you find out that no one has ever detected a gravitational wave. People have been trying for quite some time.

I often see graphs which explain this lack of detection. Basically gravity waves may just be too subtle to be detected by current methods. The answer is to build larger, more complicated observatories (in space preferably). The plans are already made. If they don’t find them then, either a new idea gets floated, or a new graph gets drawn and an even bigger detector is created.

I hope they find them before too much money gets spent!

The Higgs Boson - [Read More about the Higgs Boson]

The Large Hadron Collider (LHC) had to be shut down for a little while and so its main target: the Higgs Boson remains an unknown and unverifiable character.

Imagine you had a really nice cake. You studied this cake for a long time and you managed to figure out exactly how it was made. You could tell me the proportions and nature of the original ingredients, the length of time for which it was baked even the exact colourings used in the icing. What you don’t know though, is the type of spoon that the cook used. Without knowing this you will never truly have understood how the cake was made - and you will never managed to recreate it. If it turns out that there was no spoon then your whole theory falls apart!

The Higgs Boson is that spoon.

Without the Higgs Boson the whole framework of our understanding of particle physics is incomplete. The LHC should be able to detect it. If it can’t, then there may be a problem and the standard model of patricles will need to be reconsidered. If it is found, then we would have a complete understanding of the particles that make up the Universe. That would be profound and powerful. We may find out one way or the other in 2009.

Panspermia - [Read More about Panspermia]

How did life on Earth begin? Well one idea is that it came to our little rock from space. This notion is called Panspermia and it is actually as old as modern science. Early musings on evolution in the 18th Century considered that the original germs came from space.

Fred Hoyle (who died in 2001) and Chandra Wickramasinghe (who is now based in Cardiff’s astrobiology centre) were early proponents of Panspermia in its modern form. They also suggested that lifeforms continue to enter the Earth’s atmosphere, and that they might still cause epidemics and provide new genetic material for the planet.

The problem with Panspermia is that it solves a complicated problem (how did life spontaneously begin on Earth) with an even more complicated solutiom (how did life spontaneously begin elsewhere and then travel across billions of miles of interstellar space). For this reason, many need a lot of convincing about the idea.

String Theory - [Read More about String Theory]

String Theory is the name given to a branch of physics and maths that aims to describe the Universe in terms of multi-dimensional vibrating strings. No this isn’t Pratchett. It would be a way to combine the as-yet irreconcilable theories of quantum mechanics and general relativity - this is something of a holy grail in modern physics.

String theory is a broad name for a collection of theories - some of which disagree with each other - but all of which boil down to the principle described above. The trick is, you cannot disprove string theory. You would need an experiment so large and powerful that it would require orders of scale larger than our Solar System. We are a very, very long way from achieving this.

The strings themselves would be so fantastically small as to be possibly prohibited from measurement by nature itself. Lengths and timescales so minute that we could never measure them.

One hope for string theory is that we may see evidence of hidden dimensions when the LHC begins operations. However this could also be evidence of other things, and not necessarily a win for string theory.

For these reasons, many consider string theory not to be science, but rather mathematics. One day in the distant future we build the right apparatus and experimentally test this outlandishly cool idea. It may be right - or it may just be a mathematically self-consistent way to explain particle physics and gravity.

Summary

Popular ideas are not always good ones, nor are they necessarily bad. The work being done to advanced science in the five areas above is extremely important. However so is the work being done to provide alternative ideas and theories. Nothing in science is proven until it is proven.

A while ago I posted about the Bullet Cluster, and an image which seems to reveal the dark matter within it. Now a new image from Hubble seems to do the same thing for the galaxy cluster CL0024+17.

Now I am personally rather sceptical about the validity of images such as these, although I feel sure that we will see many more of them in the coming years. ‘Showing’ dark matter sounds to me like a dangerous business. It is, after all, dark. I would argue that releasing such images is detrimental to science and astronomy more specifically. To fool the general public into believing that something exists before you are sure of it yourself is not good science.

Now it may be beneficial to model dark matter in the way shown in these images, and this could lead to a better understanding. To release this sort of thing without warning as to the subjective nature of its content is not fair on those who would simply believe it as a photo like any other. After all how sure can anyone be that what is shown here is anything real at all? It is like deducing the nature of the wind from the way birds fly.
There is more to it that just that though. I know so many people who have no clue that many of the images they see from space are false-colour, for example. I also have to explain to people everytime I shown them Andromeda through a telescope, and look back at me confused, that the images they see from Hubble and other big observatories are enhanced, essentially doctored, to make them prettier. Do you think they will understand that this dark matter ring is simply a mathematical deduction? Will they even care?

Maybe I’m overreacting, but I do believe that one of the jobs of any scientist is to report back their findings to the public at large, who ultimately fund them. The PR guys need to get educated as to what this image and the ones that are surely coming our way soon, really mean.

Dark matter is still not a subject that we know much about. Its a mystery - and that is one very good reason it is so interesting. We cannot photograph it because we don’t know where it is. Gravitational lensing tehcniques can begin to help us locate it but don’t let’s be fooled by what the com puters give us at the end of the day. If we start to believe these images are real simply because they look real we will have strayed off the correct path and begin putting garbage into our theories. This is, as my supervisor always says, never a good thing because you end up with rubbish results; garbage in, garbage out.

You can read more over at Astronomy Picture of the Day and the Bad Astronomy Blog.

The image above shows the Bullet Cluster. Also known as 1E 0657-56, this is a pair of clusters of galaxies some 3.4 billion light years away. As Jon Davies told us in yesterday’s Astrolunch meeting however: you should be careful about believing everything you see. This image is not a regular photograph by any means. You can see the galaxies scattered about with an orange glow. This much is familiar. Layered onto this optical data is the pink, X-Ray picture from the Chandra telescope. This pink light is actually the high energy X-Ray radiation from a hot gas that permeates the cluster. Again though it is not unusual to see two different wavelength regimes seen in the same photograph.

What is unusual is that the blue ‘light’ seen here is not photographic in nature at all. It is the location of the mass in this region deduced by weak gravitational lensing - it is not a real effect but rather a mathematical interpretation of where the mass should be. As you can see it does not line up with the visual traces of the mass that we see as light and X-Ray material.

This is because it is believed that the Bullet Cluster shows us quite nicely where the dark matter can be found in this cluster. The interpretation of this image by the researchers who have studied it is that the hot, pink gas is the energy released by ordinary matter in this pair of clusters as they have collided with one another. The energy of the collision has excited the gas to emit in the X-Ray.

However not all the mass in the region is ordinary (something believed to be true about most of the universe). Dark matter is material that has mas but doesn’t interact with other, ordinary matter by the usual routes. It does not feel magnetism, or electrical forces or emit light. But is stays tethered to the ordinary matter by gravity alone.

As these two clusters collided the dark matter passed through like an ordinary pair of gaseous objects would, where as the regular, every day material became heated and disturbed and distorted in shape.

There is a wonderful video of a simulation of this hypothetical collision which you can find here.

This lovely picture adds to the already heated debate among the astrophysical community as to the existence of dark matter.