For those who need a reminder: the twins paradox is a scenario in special relativity. To understand the paradox you only need to know one thing: moving clocks run slower than stationary clocks.
You have two twins: A and B. A remains on Earth. B boards a spaceship and whizzes off to a distant star and then returns. A sees the clock on B's spaceship running slow, so B will be younger than A when B returns. However, everything is relative. From B's point of view it is A that has been moving and so it is A's clock that runs slower. So A should be younger on B's return - an apparent contradiction.
Some texts are content to point out that there is a clear asymmetry in the twins' behaviour. B gets accelerated and decelerated several times, whereas A does not and therefore the "paradox" is a non-starter. Others describe solutions to the paradox that ignore the accelerations and decelerations, which is a shame, because a lot of the interesting physics takes place during the accelerations and decelerations.
I'm going to explore an approximate approach, where the changes in velocity happen very quickly, but not instantaneously.
The diagram above is a space-time diagram. It shows the position in space and time for twin A and twin B. Twin B moves off to the right towards the star and also travels upwards through time. Twin A stays still, but also moves upwards through time. Twin B reaches the star and then returns home to meet A back on earth again.
Saturday, 26 May, 2012, 08:25 AM - Courage, hope, perseverance etc., Invisible magic stuff, Sport, MarshallRating 4 out of 5 (Highly platitudinous)
There are lots of amazing people. There are amazingly brave people, amazingly creative people, people with amazingly endurance, amazing talent, amazing amazingness.
There's Chen Guangcheng, the blind Chinese human rights activist. He's amazingly brave.
Then there's Jessica Ennis, the sportswoman who's amazingly sporty.
Wes Anderson's amazing too. He's an amazing director.
There's just so many amazing people being amazing at stuff. It's just amazing.
Which brings me neatly onto this weekend. There's a big Christian festival coming up. Happy Pentecost everyone! Shortly after the visible bit of the Invisible Magic Friend went up into space on a cloud, the particularly invisible bit of the Invisible Magic Friend came down as tongues of fire and the apostles were filled with the spirit. The more filled with the spirit they became, the more they started to talk funny. In the end, they were so full of the spirit that some people mistakenly thought they were drunk. But they weren't drunk, they were just very full of the spirit.
And in conclusion, this is why people are inspired to do amazing things.
There's a big Jewish festival coming up. Happy Shavuot everyone!
Shavuot celebrates the Invisible Magic Friend revealing himself on the top of Mount Sinai. He felt he could reveal himself to Moses because he knew him pretty well by now and no longer felt any sense of embarrassment at revealing himself.
The Invisible Magic Friend formed a contract with the Jewish people, where he told them what to do and they did it. "Go create a new society," he said. "A society of peace, justice, liberty, compassion, mercy, generosity and many, many other fine words. Cancel your debts every seven years, or possibly every fifty depending on what sort of mood I'm in. Create a society with thousands of obscure, often cruel and unnecessary regulations, with harsh punishments for non compliance, up to and including being stoned to death. Start creating this society of peace, justice, liberty, compassion, mercy and generosity by exterminating all the people who currently live there."
Thus did the Jews discover that they were on their own and they would have to build a society of of peace, justice, liberty, compassion, mercy and generosity, all by themselves without any help from the Invisible Magic Friend. Although he did pop in from time to time to see how the cruel and unnecessary regulations were being followed.
Now to some current news. Eugene Polly, the inventor of the TV remote control has died. You all seem to think that you can change the world using your TV remote control. Well I'm sorry to break the news to you, but you can't. In order to change the world you need to get off your lazy, fat behinds and actually do things. You have to do what the Jews did when they created a society of peace, justice, liberty, compassion, mercy, and generosity. The Big Book of Magic Stuff would undoubtedly have had some interesting punishment for users of TV remote controls, if only they had been invented back then.
I'm sure many of you will have been shocked to read the latest report from the Church Urban Fund. This found that many people in Britain today are poor, or old, or lonely. Some are poor and old, others are poor and lonely. Yet, others are old and lonely. Some are poor and old and lonely, and sick too, some even die.
Being old and poor and lonely is not very nice. Humans like to eat together. This is so unlike our past, when we each went off to our separate caves to eat in private, or with all other modern primates who always go off to distant parts of the forest to eat away from the group.
This is why the Christian ritual of holy communion is such fun. When it comes to a jolly good knees up, nothing can beat holy communion. But many sick, old, poor, lonely people can't get to holy communion any more - their party days are behind them.
It would probably take government policy changes to eliminate poverty, sickness, old age, loneliness and death. However, we can do our bit by offering a shared meal to our lonely, elderly neighbours.
I've just started gardening. Others are busy destroying modified plants. Some think GM could provide more efficient crops, others think it is meddling with nature.
The idea that our minds are distinct from our bodies is undermined by science. Even plants display an awareness of their environment and respond accordingly - a kind of primitive consciousness. We also consciously interact with and modify our environment, so it is difficult to see why GM crops should be any different.
One Buddhist meditation reflects that all that we are comes from nature and returns to nature. We are part of the world around us. The world is full of life and our life is part of that world. This view informs our ethical response to environmental crises in various unspecified ways.
And the big news that everyone's talking about today, is what was on the telly last night. It was the second episode of 56 Up, the series that has been visiting the same set of people every seven years since 1964.
The initial aim was to illustrate class divisions, even in the very young, and how this affects someone's life chances.
I'm sure you're all asking what I asked, what does this tell us about the Invisible Magic Friend? Well, there are only two possibilities: either the Invisible Magic Friend gave us free will, or the the Invisible Magic Friend charted out our whole life in advance and there's nothing we can do about it. Whether we have free will or not is therefore a theological question, because we have to decide what the Invisible Magic Friend is doing. This illustrates, once again, the practicality and usefulness of theology.
Calvin thought the Invisible Magic Friend had predetermined who would be saved and who would be condemned before he created us, so there really wasn't much point in doing anything. Others think the Invisible Magic Friend looks on us as a kind of reality TV show - an endless source of entertainment.
The makers of 56 Up may be trying to give us a window into a small group of people's lives, but they're really doing the most fascinating theology.
My son asked if I ever fear for the future? The answer is no, I don't. My future will be relatively short. I've been gainfully employed as a vicar and can retire on a comfortable pension thanks to the Church Investment Fund.
For young people, burdened with student debt, a mortgage and increasing costs of child care, a lifetime of debt seems to loom before them. The prospect of potential economic collapse in the Eurozone raises further fears of the rise of political extremism.
How does the Old Tasty mint tell us to solve the Eurozone debt crisis? Well The LORD commands that all debts be cancelled every seven years. Sorry, did I say seven years? I meant fifty, although this only applies to property in the country, unless it's part of a walled town, but not if it's a house owned by a Levite, which I think is pretty clear. The LORD also provides some useful advice on the buying and selling of slaves but I don't have time to go into that in detail right now.
Some of you may be thinking that just cancelling all debts and returning property to their former owners (unless it's in a walled town, but not if owned by a Levite) is totally impractical, and you would be right. However, it is not a request from the LORD but a command.
So maybe the people of Greece should be given a bit of time to sort themselves out, because if Greece does default, and banks start to fail, and investment funds stop paying out, even a Church of England pension might be in jeopardy.
The Olympic Torch, a great symbol of light, has arrived in Britain.
Light and darkness, darkness and light, these are in many ways opposites. Ancient Greek mythology understood the difference between darkness and light. I can get to mention Zeus and Prometheus here, whom you will doubtless recall, were made up. For them, one was dark and one was light, in many ways symbols for all that is dark and all that is light.
The gnostic gospels, which you will doubtless recall are not proper gospels, used darkness and light, night and day, sunset and sunrise as symbols of the battle between darkness and light, night and day, sunset and sunrise.
The Olympic Torch, a great symbol of light versus darkness, day versus night, sunrise versus sunset, will be carried around the country by 8,000 runners, some of whom have a faith. They have faces, hands, noses, big toes, but are nevertheless, in many significant ways, different people.
The Olympic Torch will end up in Stratford, where athletes around the world will compete under the Olympic Flame, a great symbol of light versus darkness, day versus night, sunrise versus sunset, where what is to be revealed will be revealed.
Saturday, 19 May, 2012, 06:10 AM - Not TFTDFollowing advice from Stonyground, I had to google "trampoline jesus".
Naturally, no mention of trampolines and Christianity would be complete without a link to the Leaping Order of Saint Beryl.
The synagogue in Plymouth is 250 years old. Like the building itself, the small Jewish community in Plymouth has blended in effortlessly with the surrounding town.
Jews learned to do this from ancient times. Since the enforced exile, when the Jews wept by the rivers of Babylon, we have learned to keep our own traditions while blending in and contributing to our host culture.
As anti-immigration parties prosper across Europe minorities should be recognised for the heritage they bring with them, while at the same time adopting all that is best from their hosts.
It's what the Jews of Plymouth have done for 250 years and it works.