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Philosophy – Peer Assessments.


The peer assessment for this course was optional and didn’t effect the overall grade for the course. The options were:-

Week 1 — Philosophy is often classified as a purely reflective method of inquiry into reality and our place in it.  But science also investigates reality and our place in it, with impressive success.  Why (if at all) should we engage in philosophical inquiry into these matters?

Week 2 — If we can’t rule out sceptical hypotheses, can we know anything about the world?

Week 3 — Could a computer have a mind?

Week 4 — Should we be moral relativists?

Week 5
 — Was Hume right to think that one should never believe that a miracle has taken place on the basis of testimony?
Week 6 — Are there good reasons to think that scientific theories should be true, rather than “merely” empirically adequate?
Week 7 — Is time travel logically possible?
I chose the last question as it was still fresh in my mind and I found the subject very interesting.

Here is my essay.

 Is time travel logically possible?

I believe time travel is logically possible. Defined as internal time and external time moving differently so that a human could be ‘x’ older whilst the rest of the world is ‘y’ older or younger.

“People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion.” ( Albert Einstein). Einstein extended Galileo’s principle of relativity, accounting for the speed of light, to create his ‘special theory of relativity’. This theory linked time and space into a ‘space-time continuum’ of four dimensions. If you move fast enough through space then you can travel forward in time.  Einstein died trying to figure out how he could unify electromagnetism and the general theory of relativity.

Einstein’s theory was developed by Paul Langevin and later Max von Laue to become the ‘Twin Paradox’.  An  example of this (Wikipedia) illustrates how if a ship travelling at 80% the speed of light (671 million mph)  took one twin to our nearest star it would take six of his years but ten earth years. On return to earth he would be four years younger than his twin. A logical possibility except that we can’t yet travel that fast. According to Aerospaceweb the fastest manmade object was Helios 2 (1976) which travelled ad 150,000 mph, more than six times faster than Apollo 10 (1969).

“Time travel, I maintain, is possible. The paradoxes of time travel are oddities, not impossibilities.” (David Lewis – The Paradoxes of Time Travel). All the paradoxes and objections to time travel appear to suggest that we would be travelling in the same dimension as we already are, were and will be. The arguments are that a person cannot be in two places at the same time, nor could you effect a past that already exists.  Much of Lewis’ argument rests upon the paradoxes of time travel and how they can be overcome.  His theory relies on space and time being in four dimensions so that you can be in different time planes from different view points.

Theodor Kaluza’s (1919) idea of a fourth ‘curled up’ dimension was refined by Oskar Klein. ‘String theorists’ have used those theories and Einstein’s ‘special theory’ to posit that there might be more than ten dimensions. The string and superstring (M) theories are in their infancy but the confirmed existence of the Higgs boson has progressed their understanding of quantum physics.  The machine that produced this can move particles at nearly the speed of light. They can get to 99.9% the speed of light but never exceed it although only 80% is needed for the Twin Paradox.

“I have experimental evidence that time travel is not possible. I gave a party for time-travellers, but I didn’t send out the invitations until after the party. I sat there a long time, but no one came.” Stephen Hawking, despite his scepticism also spent a long time working on the theories of time travel. His work revolved around using worm holes and black holes as a medium for crossing from one time plane to another. He describes black holes as ‘time machines’. The disadvantages are that they are far away and don’t take us very far in time. Worm holes that are around us are too small although Professor Hawking believes we may one day be able to expand them to a size big enough for a human or a space ship to travel through.  He has not, however, come up with a way to maintain the expanded wormhole in place long enough before it is destroyed by radiation feedback.

In conclusion: Scientific theories determine that if we can travel fast enough we can time travel. The speed at which we can make particles move has reached a stage where it would be fast enough to do this. The amount of energy needed to move anything that fast is enormous but we are creating new forms of energy all the time. Professor Stephen Hawking said that if time travel existed we would see time travellers. If time travel existed but travel was only possible to a different dimension, then we wouldn’t be able to see them.  String theory offers us many more dimension.  I believe that one day we will be able to travel fast enough and have enough energy to do this. In order to save the paradoxes we would only be able to travel to a different dimension.

Primary source of information – Wikipedia, course notes and howstuffworks website.

My overall result for this essay was 17 out of a possible twenty-one. Here are the remarks from my three peer assessors.

peer 1 → A. It was interesting and presented different points of view. B. The author focused more on time traveling to the future and pretty much forgot the past. This made his arguments less strong. He also didn’t include objections to his thesis that were clear and didn’t counterargument them.
peer 2 → Your essay was very clear and well-organized. The only criticism I have is your use of quotes at the beginning of paragraphs. That’s generally bad practice. You should start by stating the point you want to get across in that paragraph, then use quotes as supports if need be. Since this was such a short essay, I guess I can’t fault you for not properly citing the quotes. As far as the argument goes, unless I misunderstood you, you only gave an argument for forward time travel, not for backward time travel. But most (or all?) of the paradoxes come from backward time travel, so you needed to make an argument for backward time travel, or else explain that the paradoxes don’t apply to forward time travel. Over all good job, though.
peer 3 → Student 3 Hi As a former student of physics, I was interested in your choice of scientists’ quotes. I opted for the week 6 topic and chose Albert Einstein’s 1905 papers as exemplars of scientific theories. Some of your science is dodgy. Einstein’s quotes about past, present and future refer not to time travel but to the scientists’ reluctance to engage with ‘tensed time’, that is the individual ‘now’, the past and present. Einstein’s thought experiments used an impersonal observer and sequences of events. There are other quotes that suggest that although a fan of physics you don’t understand the physics. You present a (sympathetic) assessor with a problem. You state one question and answer another and make few references to the lecture material. Virtually the whole of your assignment addresses the question of the possibility of actual time travel, – the question asks about the logical possibility of time travel. The first sentence of your conclusion states ‘ Scientific theories determine that if we can travel fast enough we can time travel’. Which doesn’t tally with your first sentence ‘I believe time travel is logically possible’. I don’t need to state the obvious. You will have looked over other students’ assessments and realized that marks come from a clear structure, inclusion of the main pints from the lectures – as highlighted by the quiz and a critical look at their implications. Arguments can run take on a life of their own and it is worth checking the conclusion against the question. And rewriting to improve argument and presentation. Some intuition is needed but you may already have it, or you can find it on the internet. I would suggest Lewis’ view that a time traveller can ‘affect’ her own present; but there are lots of others pointed to on the internet. Please take these comments constructively. Best wishes.


  1. gbl55 says:

    Very good Louise! I got 19 on the same topic but yours is more interesting – as an ex-academic I know how to churn out stuff to a formula. Also, you have received far better feedback than I did – only 2, 2 and 1 line for me. I’m not too impressed with the assessment system but of course there are big problems in a MOOC – early days!
    Gordon Lockhart

    • Louise Taylor says:

      Thanks Gordon and congratulations on your 19. Will you be posting your’s to your blog? I find writing the essays the hardest thing about the courses I am doing. I haven’t really done anything like that since I was at school as I did financial stuff at university. I agree that the peer reviews are not superb but for a free course I don’t think there is another option. I am always really disappointed when I don’t get a lot of comments.

      • gbl55 says:

        I hadn’t planned to post mine but now somebody else has posted their’s on introphil so I’ve just put mine in the forum where there seems to be quite a lot of activity under your post!

      • Louise Taylor says:

        Yes I just read your there. It is very good and answer the question with all the references. I think I missed the point a little and talked about the physical possibility rather than the logical possibility.

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