The universe has four entities, space, time, matter & energy. The latter two are manifestations of the same entity. According to Albert Einstein's theory of relativity the first two are combined in a single entity

"space-time".

The Universe, all that we can detect with telescopes, radio telescopes etc. is usually thought of as residing in space. How much more there is we will probably never know, or what lies beyond. There is a theory that if we go far enough, we will arrive back at the beginning. This is conjecture, unsupported by evidence.

* Reality of outer space.

The reality of outer space is that it does not exist, it just is not there. Space is simply the gaps between actual entities, whether these are matter or accumulations of energy. In other words there is no space if there is nothing to contain it.

This presupposes that space is finite, there is space between us and the farthest star but none beyond. If that star moves further away then the amount of space gets greater. There is potentially no limit, but it remains finite.

Aristotle gave us the concept of potential infinity. Nothing is actually infinite, but if it can increase without limit it is potentially infinite. He also said that being able to divide things without limit presents another form of potential infinity. This is true of numbers but we are pretty sure it is not true of matter.

if expansion eventually comes to a halt, gravity will start the Universe's contraction, space will get smaller. If the singularity theoty is correct, all matter will eventually become concentrated. The enormous gravitational attraction finally reducing the universe to a single point, possibly of zero size & infinite density. There will be no space, & presumably no time.

Cyclic theory.

At that instant, when time stops, its momentum will cause it to reverse. An unimaginable explosion, the next 'Big Bang'. All of history may repeat itself, or follow a different course. We will not know, we will not be there to know, or how many times this has happened before.

The big bang, singularities & all that they entail are theories. Continued observation & thinking may show the likelihood of them being correct or suggest better theory. Theories are our way of trying to explain what we can observe, or of visualising what we can not observe.

Time.

Time, the 4th dimension. The continuum of existence from the past, through the present, into the future. The passage of time is essentially negative, the universe, at its creation, was accorded a quantity of time. Possibly an infinite amount, probably finite, we don't know. Every instant that passes is subtracted from that quantity. Everything we do or avoid doing uses up some of our time, which is definitely finite.

The past is time that has elapsed & is no more. The future is time yet to come, what it holds for all is a matter of conjecture. The present is a dividing line between the two, a fleeting instant that we are currently experiencing. For us this is the only reality.

According to relativity, movement slows time, at the speed of light it comes to a halt. Experiments with a caesium clock on a jet aeroplane appear to confirm slowing. The results are probably suspect, travelling a few thousand miles, at a few hundred miles per hour, makes a tiny difference. It is doubtful that current atomic clocks are sufficiently accurate to reach a conclusion.

In any case relativity itself can provide another answer. The electrons of atoms rotate at the speed of light, they can go no faster or slower. It follows that when the clock is moving, its atoms must slow their rotation, to maintain that absolute speed. The clock will lose time, it is as simple as that, or is it?

So it seems it is not time that is slowing, just the clock. So airline passengers can not expect to stay young a little longer.

Travelling much faster, for a greater distance, gives a better clue. The caesium & rubidium clocks used in global positioning satellites have to be compensated. They lose a few nanoseconds during the launch & continue to lose slightly due to their high orbiting velocity. The necessary correction has to be programmed in before their journey.

Satellites may age more slowly, simply because their atoms are working at a lower rate. So relative time is slower, this also applies to their payload. The figure is about one millisecond per year, dependant on orbital radius. Absolute time, as perceived by us, is not affected.

So the G.P.S. has finally confirmed the theory of relativity, at least in terms of time. Taking account of relative time shift is now a practical engineering necessity.

It may turn out after all that travellers heading into outer space will age slower. Although they won't notice it because, relative to them, nothing has changed. On their return they will be younger than those left behind. Although years in a cramped space craft may have taken its toll.

This is usually called time dilation, it is not the same as time travel. Our equator is moving at about a thousand miles an hour due to the earth's rotation. Everyone there should live a tiny bit longer than those at the poles. Probably the weather will make a greater difference.

A practical experiment will involve two identical precision clocks, probably based on hydrogen masers. One placed at the equator, one at a convenient spot for observation, nearer a pole. Aberdeen is a likely candidate.

Initially synchronised by a radio signal, to take account of light speed. Then left for a year or more to check for any shift. To allow for possible errors in the clocks, two can be arbitrarily selected for each location.

Inter-Stellar Travel.

Travelling to the stars is unlikely to be as easy as in Star Trek. The nearest system is some light years away. The journey will be less comfortable than Voyager. Mass increases with speed, as any of us who have hit their thumb, whilst hammering in a nail, can testify.

If the Theory of Relativity is correct we will have problems. At the speed of light, being squashed into zero space by our infinite weight will not be pleasant. To make matters worse, time, & all our atoms will stop. Fortunately, this situation requires more energy than the universe holds.

Anti-matter, as a source of power, warp drive & wormholes through space appear to hold out some hope. There is however, no evidence to suggest the possibility of any of these. Interpolation from current verifiable theory also does not support such concepts.

Because some predictions from science fiction have proved correct, we are in danger of starting to believe any cockeyed concoction.

I enjoy Star Trek, however I also enjoyed reading Alice in Wonderland. I have no illusions regarding talking rabbits.

A practical space craft, Noah's Ark revisited.

Reality is much simpler, to build a craft capable of travel to the nearest star will take enormous resources. The entire world will have to co-operate & make considerable economic sacrifices. The vehicle will be very heavy, fuel being the major portion. It must be assembled in space, that much material can not be lifted from any planet in one go.

To avoid depleting Earth's resources, other planets must be mined for materials & fuel. The Moon & Mars look most likely. Nuclear fuel is the only practical source of energy for a long journey, a huge amount will be required. Presenting problems with containment, handling & shielding. If electromagnetic shielding is possible, it will use energy.

The craft will need to be sufficiently large to house an entire biological environmental system, a new Ark. Capable of sustaining life through many generations, during the journey. Humanity, with other life forms, will evolve in a near zero gravity situation. This will cause problems if a suitable planet is reached. We still do not know what gravity is, let alone how to control it.

All the time the available energy will be reducing, a lot will be used during the initial period of acceleration. After that the ship must coast to conserve the remainder. Sufficient must be available for braking & landing craft upon arrival at the new home planet. Due to its size the large surface area will radiate heat constantly, to the near zero temperature of outer space.

Heavy internal insulation will help, but will cause another problem. The outer hull will approach zero degrees Kelvin. This will make the metal brittle, easily damaged by impact with space debris. External insulation may be better, but will likewise be easily damaged.

Maximum journey velocity will depend on the amount of fuel that can be expended. One would hope by that time we will crack the fusion problems. Possibly a combination of fission to kick start fusion. Light speed will not be approached, relativity will see to that.

We are used to talking about high speeds of thousands of miles per hour. Light travels at over 670 MILLION miles an hour. So the time dilation advantage of such speed will not be available.

Assume that an average speed of 1 million miles an hour is reached. That is around 40 times the earth's escape velocity & requires a lot of fuel. The nearest star is Proxima Centauri, 4.22 light years away. A journey of 2,827 years, 95 generations, assuming 30 years per generation.

It will be a major achievement to build a craft able to function that long. What a disappointment if no habitable planet is found.

Proxima Centauri is a red dwarf, not a good candidate for living quarters. A better bet will be Alpha Centauri A or B. These are a binary system, a seventh of a light year further away. One may have an Earth class planet, 'A' is more like our Sun.

Of course things change if Special Relativity is wrong & we run on Galilean or Newtonian time. There will be no upper limit on speed, time dilation is however lost. No time travel paradox, but to reach trans-light speed still requires a source of power we have not found yet. No curved space means no wormholes & seems to preclude warp drive per se.

There is then another obstacle to faster than light travel. Sir Isaac Newton's third law of motion. To every action there is an equal & opposite reaction. To move a million tons of vehicle at the speed of light requires ejecting a million tons of plasma at twice the speed of light (relative to the ship). At journey's start that million tons will be on board & will thus also have to be accelerated.

Plasma is the only practical way of turning nuclear energy into thrust. Unfortunately plasma is energy with mass & thus can only travel at the speed of light. Even Newtonian physics accepts that. So ejecting 50% of the start mass as energy can only achieve half light speed. Oh dear, & we have forgotten about fuel for slowing down.

To be continued.

We Wish ALL the Universe Peace, Justice, Equality, Prosperity & an End to Fanaticism