It’s ‘Wellness Focus’ week here, and there are all kinds of wonderful activities going on to promote health among the employees of the University of Waikato. I’ve just finished a REV class, which has finished me off for the whole afternoon, I think. Yesterday, I had a free health check – where my blood pressure, cholesterol etc was measured, and the nurse went through a lifestyle questionnaire with me assessing my risk of heart problems (which turns out to be low). One question on the list is ‘what is your age?’. It obviously affects your risk of a heart attack, though the nurse said it’s one factor that you can’t do anything about.
Well, I thought, that depends on how pedantic you want to be about it. I’ll be travelling to Sydney very soon as part of my study leave, and that is going to slow down my aging by a few nanoseconds. That’s simply a consequence of special relativity. The important factor here is denoted by the Greek letter gamma by physicists, and is the reciprocal of the square root of [1 - (v^2/c^2)]. In this expression, v is your velocity, and c is the velocity of light, or 299,792,458 metres per second. (The ^2 means ‘square’). It tells you how much time slows when you are travelling at this speed.
What is gamma for a commercial jet aircraft? At 900 km/h, or 250 m/s, it comes to 1.00000000000035 . That means, when I’m on board the plane, for every 1 second of aging I do, people on the ground will age 1.00000000000035 seconds, that is and extra 3.5 times 10 to the power of minus 13 seconds. Over the course of a three hour flight that comes about an extra 4 times 10 to the power of minus 9 seconds, or 4 ns. Not enough so you’d notice, but it’s measurable with atomic clocks.
One of the problems with teaching special relativity is that its effects nearly all lie outside the realm of everyday experience. They are only apparent when something travels very fast. However, they are extremely important in physics. That’s the motivation for this piece of software I was told about a couple of weeks ago from the Australian National University in Canberra. The software, which you can download for free, lets you fly a spaceship around a city-scape at close to light speed, and observe some of the effects that are occurring, or observe different clocks at speed to see the time dilation effect. It’s well worth a play, but to get the most out of it you should follow through the student instructions which come with it. The research article that comes with it is worth a read too.