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Asked by to Becky, Clara, Daniel, Simon, Thomas on 16 Mar 2014. This question was also asked by .
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Clara Nellist answered on 16 Mar 2014:
Everything we see around us is made up of matter. Mostly this is protons and neutrons (each made of quarks and gluons) and electrons. But there are also a bunch of other particles that make up our stuff called matter, such as muons and taus (the heavier cousins of electrons), neutrinos (which are extremely light and difficult to detect) some more quarks and some particles called bosons that transfer different forces (this includes the Higgs boson). We also have all of the same again, but as antimatter, instead of matter. The difference between a matter particle and an antimatter antiparticle, as far as we know, is that where one has a negative electric charge, the other has a positive charge (and the other way round, if a particle is positive, it’s antiparticle version will be negative).
So that’s great! But it turns out that this only accounts for about 4 or 5% of the stuff we’ve measured in the universe. There’s still about 95% of the universe that we don’t know about! Which is a bit crazy when you think about it!
From measurements, we think that about 25% of this remaining stuff is something we call ‘dark matter’ – it’s dark because we’ve seen evidence that it’s there, but we can’t actually *see* it as it doesn’t give off light or other radiation that we’re familiar with. One of the experiments that tell us it’s there, comes from measuring how fast galaxies spin. Scientists have measured the amount of matter in galaxies, and so thought these galaxies should spin at a certain speed. Then they measured this, and found it was going faster than expected! This told us there was more stuff than we can see and we called it dark matter. So far we have no idea what this stuff is. Some scientists think it comes from a whole new set of particles we haven’t been able to detect yet, and experiments at the Large Hadron Collider at CERN are trying to look for these new particles. If they’re found they could explain what dark matter is and it would be a very exciting discovery!
Then, we have the remaining 70% of the universe. That’s even more of a mystery!! This was suggested by scientists as a possible explanation of why our universe is expanding. We know it is expanding because we’ve measured that galaxies are all travelling away from us. Assuming we’re not in a special place (which is a good assumption to make) it means that all galaxies are travelling away from all other galaxies and the space that they’re in is expanding. To help you to understand this, draw some dots on a balloon. These are your galaxies. Now blow the balloon up. You can see that the distance between each galaxy increases. If you were on one of those galaxies it would look like the others were travelling away from you. Unfortunately we don’t know what this dark energy is or where it comes from!
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Thomas Elias Cocolios answered on 16 Mar 2014:
According to our best understanding stemming from General Relativity and Cosmology, the universe is made of matter, dark matter & dark energy.
The ‘matter’ is what we can see with the naked eyes. It consists of the galaxies and such, even the black holes (though ‘seeing’ them a bit of a contradictory statement!). It represents the least of what the universe is made of, that is a few % only.
The ‘dark matter’ is stuff that we cannot see. Some people proposed it could be lost planetoids and such that would be dark in the interstellar medium, however that could hardly account for all the dark matter that is predicted in the universe. Instead, the cosmologists and astro-particle physicists are continuously searching for new forms of matter, called dark matter, with tools such as the Alpha Magnetic Spectrometer (AMS), a satellite built at CERN with the same technologies as the LHC detectors, which is currently collected data from the universe on the International Space Station.
There are also other mechanisms proposed to study such ‘Weakly Interacting Massive Particles’ (WIMPs): it is proposed that they may interact with elements, e.g. argon, making them radioactive. By collecting samples from very deep in the ocean (where no other mechanism can produce radioactive Ar), we can put a limit on such processes by comparing the number of radioactive and stable argon isotopes (like carbon-14 dating). This particular topic is one that I shall soon start in Manchester with my laser technique. How awesome would it be to find the first traces of WIMPs!
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Simon Albright answered on 17 Mar 2014:
The visible universe is made up of matter.
Interestingly the vast majority of regular matter is actually plasma rather than atoms and that’s because of the stars. In our solar system about 99% of the mass is in the sun, and the sun is pure plasma!
We’re not completely sure what the rest of it is, we think it’s Dark Matter and Dark Energy but we don’t know much about them apart from what Clara and Thomas have already explained.
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Daniel Roach answered on 18 Mar 2014:
The universe is mostly made up of… nothing! Even when we’ve taken account of all the matter (which is mostly nothing – atoms are made up of mostly empty space – with a very dense nucleus surrounded by nothing and then, far away (on a nuclear scale), the electrons).
As for the dark matter – and dark energy… I work with a guy here at Salford who has very recently published a paper which deals with a small but significant correction to General Relativity. What this means is that he has provided solid mathematical evidence to show that MoND (that’s Modified Newtonian Dynamics) works. This means we don’t need dark energy and dark matter to explain the observables such as galactic rotation rates.
This is good, because all this talk of ‘dark matter’ and ‘dark energy’ is, in my opinion, rather silly! If you had an equation that predicted how much tea you had in your cup based on the amount of sips from your cup you’ve taken since you filled it. Now… after ten sips, your tea-sip-equations says you should have a nearly full cup – say 90% full. But then you look into your cup, and you see it’s nearly empty…. Wow, you say… It must be filled with ‘dark tea’ – tea that doesn’t reflect or absorb light, doesn’t interact with any forces other than gravity and hence is invisible.
It’s that silly! Rather than admitting that your tea-sip-equation needs adjusting (no way! Our tea-sip equation must be absolutely accurate!), we explain away the difference between experimental observation and theory, not by changing the theory (the correct scientific approach) but by creating imaginary observables that are (rather conveniently) very difficult, if not impossible, to actually measure. Then our reputations as ‘good theorists’ are absolutely secure.
Can anyone see any problems with this reasoning? 🙂
This is an example of a priciple called ‘Occam’s Razor’; this states that, all things being equal, the simplest explanation that covers all the observable facts is the correct one. What is more likely? That the universe is 90%+ made up of weird stuff we can’t see, can’t measure and there is no sign of on the earth or in space immediately near the earth… after all, being an ordinary planet in an ordinary solar system, you’d think we’d have at least 50% of this stuff in our tea, our chairs and the earth’s crust etc…
Or is it that our equations describing the gravitational interaction is a teeny bit wrong?
What do you think is the simplest answer?
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