What is dark matter?

John Smith Physics Essay

What is dark matter? By John Smith

The world of physics has many questions that need to be answered and analysed, so that we can unravel the mysteries of the world today.

Dark matter is one such topic that we need to investigate, with this essay I hope to give light upon the dark topic of dark matter.

Firstly, what is dark matter?

[1]Our galaxies are made up of clusters, such as stars. The clusters are held together by gravity. Scientists have tried to measure, how much is being squeezed by the gravity. The outcome from the tests is to identify, how much matter there is or the squeeze force.

However our galaxies have clusters that are invisible, meaning we can’t see it. This invisible matter is classified as “dark matter”.

The term “dark matter” was forged by Fritz Zwicky who discovered evidence for missing mass in galaxies in the 1930s. I shall explain more about him later on in this essay.

How can identify dark matter?

[2] When we think of the universe, we only think of what we can see, not what we can’t see. With technological advances, astronomers can use great telescopes to see what the naked human eye can’t see, such as light in the electromagnetic spectrum. In turn we see many more stars and galaxies show up.

Scientists understand the laws of gravity by using formulas to calculate orbits and the movement of objects that are attracting each other.

Astronomers can look at a galaxy and measure how fast stars are moving. The motions of ...

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How can identify dark matter?

Scientists understand the laws of gravity by using formulas to calculate orbits and the movement of objects that are attracting each other.

Astronomers can look at a galaxy and measure how fast stars are moving. The motions of the stars are the result of the gravitational forces from all the other matter in the galaxy.

The problem is that when astronomers add up all the matter, it doesn't add up to the motions they monitor.

According the calculations, all the matter we can see is not enough to produce the gravity that is pulling us around. Not only do stars in our galaxies move around faster than expected, but galaxies within groups of galaxies do too.

Surely there must be an unidentified force that is causing this, i.e. something dark and unknown.

The difference is that, what we know and see, or in this case can’t see, is different to what we know. For example, you know I cannot breathe fire so if I was breathing fire, you would suspect that I have oil in my mouth that is causing me to breathe fire, therefore in terms of science, the unidentified name for this force is “dark matter”.

Who came up with the theory of dark matter?

[3] While examining the Coma galaxy cluster ([4]a large cluster of galaxies) in 1933, Fritz Zwicky was the first to use the virial theorem to suppose the reality of dark matter. He was able to find the average mass of galaxies within the cluster, and obtained a value about 160 times greater than expected from their luminosity, and proposed that most of the matter was dark. The same calculation today shows clearly that the great majority of matter in the universe is dark matter.

[5] What is The virial theorem:

The virial theorem used by Fritz Zwicky to find dark matter, provides a general equation relating the average over time of the total kinetic energy, , of a stable system consisting of N particles, bound by potential forces, with that of the total potential energy, , where angle brackets represent the average over time of the enclosed quantity.

Where Fk represents the force on the kth particle, which is located at position rk.

However a big question remains,

How much dark matter is there in our universe?

[6] “The problem is no one actually knows how much dark matter there is. It’s a widely debated topic.” According to NASA, dark matter makes up about 25% of our universe today.

So where does this leave us?

Through my essay we now know what dark matter is in our universe, who discovered it and how we measure it. When will we find out the exact amount, we don’t know but what we do know is that; as science progresses we will become closer to finding the answer to the key question that shrouds us to this day.

References

The paragraphs I have wrote have been taken from the sources below and edited by me for use in my essay.

[1] date 18th February 2011

[2] date 18th February 2011

[3] date 10th February 2011

[4] date 10th February 2011

[5] date 10th February 2011

John Smith Physics Essay

Peer Reviews

Here's what a star student thought of this essay

pictureperfect

27th of Jul 2012

Quality of writing

This essay is quite well written, the candidate has used a good range of vocabulary and they have used scientific terms accurately, which demonstrates a good understating of the topic they have discussed. However there are occasions where the essay doesn’t flow as well as it could, it can be difficult to get all the information you want into an essay without it feeling jumpy. I would advise that you take the time to write out a plan and think carefully about the information you want to include. You should also read over your work as you write it, this will allow you to see if the information fits together. That said, there are no errors which spelling, punctuation or grammar.

Level of analysis

The candidate has taken the time to research this subject, this is clear, as they have provided names and dates relating to the theory of dark matter. Taking the time to research your subject demonstrates your ability to study independently which is an important skill for further education. In addition to this it shows the reader that you are interested in your subject and the extra information you are able to include in your work can make your essay more enjoyable to read. The candidate has also taken the time to write up a bibliography which is important, by declaring the resources you have used you can avoid being accused of plagiarism and you allow the reader to see the steps you have taken to prepare your essay.

Response to question

The candidate gives a thorough response, they explain what dark matter is and go on to discuss how the underlying theory was first developed. Furthermore, though only brief the candidates introduction is actually quite good, they clearly state what they will go on to discuss and they have attempted to engage the reader by stating an interesting fact and injecting a little humour. There is nothing wrong with trying to catch the attention of the reader using humour, as long as the rest of your essay is written in a more formal manor.

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