## Watch the time machine!

Place a thermometer into boiling water, and it will read 100 degrees centigrade. Now plunge the same thermometer into a bucket of ice. The difference in temperature is (at least) 100 degrees, but there is a lag with the thermometer reading. It won’t immediately read 0 degrees, but it will go through the intermediate temperatures (albeit quickly) from 100 degrees, down to 0.

It can easily be argued that the thermometer is in part reading the temperature of itself – it’s own internal temperature, rather than the true ambient temperature.

Keep this in mind as we take an instantaneous journey through time in a time machine…

In an earlier post I demonstrated how the progression of time through space is instantaneous. But how does time progress in a time emachine?

Consider this. A person goes in a time machine and is instantly placed from the present to say 100 years into the future (as far as “instant” is possible…let’s call it experienced time).

Will the watch he’s wearing read t = 0 and instantly transform to t = 100 years? Or like the thermometer, will it pass through all the intermediate times like the thermometer read intermediate temperatures? Will he?

It might seem that a watch, by changing from one state of time to another, intrinsically needs to go through the intermediate times. But this implies a non instant travel. It sounds a little paradoxical that instant time travel means travelling [instantly] through all times in between!

Alternatively, does the watch measure the moment of ambient time, such as a GPS receiver ‘checking in’ to a satellite clock signal? Or does it measure the progression of experienced time?

I mentioned that this particular time machine operates instantaneously. That is to say that the “experienced time” is zero. Ambient time, therefore undergoes an instant change. This raises the question of how is an instant change in time possible?

Let’s pause for a moment on a slight detour and consider a well known thought experiment. On a train.

A train is traveling at a constant speed of 125 mph towards the west. A fly is buzzing in exactly the opposite direction, on a collision path with the train.

The collision inevitably takes place, and I think it’s fair to say that neither the train or the fly are aware of the event.

Now let’s consider the movement of the train and the fly.

The train is moving to the west at constant speed, collides with the fly, and continues its movement to the west (with a very slightly reduced velocity owing to increased combined mass with the fly).

The fly was flying towards the east. It collides with the train, then moves with the train towards the west. This means that the fly’s velocity changes sign, i.e. it goes from an arbitrary positive, through zero, to negative.

At the moment that the fly had zero velocity, it was in contact with the train. It might seem logical to assume that the train must therefore also have a zero velocity…but we know from experience that this is not the case.

We have therefore defined an infinitesimally small moment in time, but how to explain it? (Aside – this is the great thing about time travel – one question leads to another! 🙂 )

I was spinning on a roundabout with my daughters last week trying not to retch. They were fine; they were sitting near the middle, whereas I was on the outer rim. How was it possible that I had a greater linear velocity than they, and yet we were all in contact, much like the fly and the train?

The clue is that we were sitting on the same roundabout, undergoing the same angular velocity. Even the infinitesimally small point in space in the dead centre…was still rotating at the same rate as the rest of us.

And there it is. Angular velocity. I suppose that it’s not for nothing that people talk about the wheel of time! 😉

So back to our question of how is local ambient time experienced in an instantaneous time machine. Could it be that the local time is compressed or contracted to a point of ‘zero time’, (not to be confused with t = 0, an arbitrary reference time point) and regrows back to a new time? This zero time point would be analagous to the ‘fly point’ of zero velocity, or the zero space point on the roundabout.

Progression along the radius of the roundabout maintaining constant angular velocity showed that these zero points are possible. How that can be translated to time, or get it to regrow again…well there lies the magic of a time machine!