Dark matter: how to see the invisible

Last month, looking at images sent to Earth by the Hubble Space Telescope, scientists believe that they “saw” what they call dark matter.  Seeing dark matter is something of an accomplishment because, if it exists, it is invisible.  So what did they see?

They saw a ring around a cluster of galaxies 5 billion light years* from Earth, and about 2.6 million light years across.  The ring is not a halo of light, which is what we would imagine, but rather a rippling effect created by something that is bending the light of even more distant galaxies.  Gravity is what bends light, and gravity is created by some kind of particles that we can’t see, and that scientists think is what they call “wimps” (or “weakly inter-acting massive particles” in less playful terms).

If wimps exist, they can explain this phenomenon.  We’ll never be able to get a cupful of them in our hand, but the more things scientists see that don’t make sense unless about 23 per cent of the universe is filled with them, the stronger the theory about dark matter becomes. 

Like everything else scientific though, it is only a brilliant guess based on an attempt to explain and predict what we see.  I myself don’t think there’s a better way of understanding our world than by testing our ideas using the scientific method.  But if you want absolute certainty, don’t be a scientist. 

On the other hand, if you can get excited about living in a world whose frontiers are never exhausted, where there is always another question to explore, where you are happy to gasp in wonder at a mystery the size of which you can’t comprehend, science might be your thing.

*A light year is the distance light travels in a year.  At about 186,000 miles a second, light covers about 6 trillion miles a year.


About Terry Sissons

Terry Sissons is the author of The Big Bang to Now: All of Time in Six Chunks, and this blog is a dialogue about the universe and what’s happened in the last 13 billions years.
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