Friday, 16 January 2015

Einstein and the Finite Speed of Light

The ideas in this article is probably nothing new to the working physicists, but to layman like me, they're mind boggling. It probably blew their mind too when they first understood the concepts.

If you think about it, some of the Einstein's best known theoretical physics simply arose out of the fact that light is traveled in a finite speed (as supposed to infinite speed or instantaneous as it was once thought of).

When we look at the night sky, astronomers tell us that because of light's finite speed, depending on the distances of the stars from us, some of these lights we see are thousands of years old, and some are millions of years old. In other words, the further the stars are located from us, the further we're looking back in time. You could say that in a sense, the telescope is a time machine. It allows the astronomers probe into the different time frame of the universe in the distant past by looking at the light of the stars at various distances from us. Much in a sense how archaeologists look at the deeper layers of soil to reveal artefacts that are buried further back in time.

This is only possible because light speed is finite. If light speed is infinite, then it doesn't matter how far the stars are from us, the astronomers will see all astronomical events at the present time as we do so on earth (well, in practice, but not in principle. In theory, we can only look at things in the past, albeit it's a very tiny fraction of a second in the past).

Andromeda Galaxy.  Photo source: wikipedia

Because the speed of light is finite, you can no longer considering the vast distances of space without considering the huge stretches of time, hence they become inextricably linked like a pair of Siamese twin. We can no longer just talk about time and space as separate entity, but a single space-time continuum that forms the very fabric of our cosmos.

Even in daily language we also mix these 2 entities in an interchangeable way. E.g. when we talk about a "distant past", where "distant" refers to to space while "past" refers to time. Of course, the term "light year" is the very essence of what I've been talking about. It's using time "year" to measure space.

Einstein's whole Theory of Relativity was born because of light's finite velocity. But Einstein's most famous equation, probably because of its simplicity and power of expression, also contains this all important speed of light. This beautiful equation is in fact came out of the Theory of Relativity. It's almost like a footnote. But what a footnote !




Another thing I realise too is that it isn't just the finite-ness of the speed of light that gives rise to the very fabric of the cosmos, but its actual values could also define the property of our physical world.

Like the numerical value of our height or weight, which shapes us physically; the actual numerical value of the speed of light also shapes the very nature of our physical world. Although the speed of light is a far more complex measure than our weight or height. Perhaps our IQ or temperament would be a better comparison.

Our world will be drastically altered if we have a different speed of light. Let's look at a simple everyday world examples.

Firstly, this equation tell us that energy is proportional to mass, and this proportionality is given by the constant velocity of light squared. This equation tells us that for a small amount of mass, huge amount of energy can be released if that mass was to convert into energy. It's huge amount because the value of c is so large.

Let's look how the effect of different speeds of light can have on our history. Let's play God and change the speed of light to 100 times slower (still a tremendous fast speed).

Little Boy
Little Boy

The filling weight of the uranium in Little Boy - the name of the atomic bomb dropped on Hiroshima - is a mere 64 kg. The overall weight of bomb was 4,400 kg.

If the new c is 100 times slower, which makes the same filling weight of the uranium in Little Boy to be some 640,000 kg to produce the same energy. This is just the filling weight. The weight of the bomb would be far in access of that. There was no plane in WW2 that would able to carry the Little Boy that heavy.

The outcome of the war would surely be different. But it was what happens after this war that would be even more dramatic because the mass requires to build a nuclear weapon would render them impractical. We would be now living in a world that's free of nuke weapons.

This could be a blessing, but could be the worst possible scenario for mankind because it's the MAD principle that kept the superpowers from going to war with each other. Without this deadly weapon, there may not be a Cold War, but an actual armed conflicts between the 2 ideological foes of USA and Soviet Union. And that would be WW3. A frightening scenario.

One can only speculate what would happen in a world without nuclear warheads. One thing for sure, it would be different. All these is a simple change in the numerical values of the speed of light.

Similarly, one can imagine what if the numerical value of c goes the other direction. I.e. Light travels 100 times faster than in our current universe.

Nuclear weapons would be so easily deployed because of its small size that it's a miracle that we will be able to survive to this century. Any mad man and terrorist would be able to carry a bomb in his/her luggage that has the power of 100 times more than the Little Boy.

Nuclear power plants
Nuclear power plants (photo: wikimedia)

If we do survive, nuclear energy would make up a far larger fraction of total energy generation than we do today. Our landscape would be littered with far many more nuclear reactors than we have today because for the same amount of radioactive risks we have today, we obtains 10,000 times more energy out of it. This much lower risks to rewards ratios makes nuclear power plants more attractive, and therefore more popular. Who know?

The actual equation that relates matter and energy is a little bit more complicated and messier than E = mc², and therefore less elegant. For the general public like me, elegance is more important than accuracy. Still, it doesn't change what I said drastically. The principle remains the same.

I'm sure there're other equally drastic changes in our world, history, evolution, and just about everything else if the speed of light is different than we have today. Speed of light is probably a figure that effects us more than our IQ number.

Of course, we can really just change the value of the speed of light and expect everything remains the same. If we can change the speed of light, our universe will be so drastic difference, and evolution will be so different that we may not have human evolved on planet earth or any where else.

One point I think I have not brought it out too strongly. All this, the fabric of the cosmos, profound revelation about energy and matter, and much more all down to the study of light. Pause and think about it. What so special about light and its property that it leads us to the understanding of the greatest mystery and fundamental nature of the cosmos?

Ronald Mallett


Let me just throw in one more latest research into the mix. Ronald Mallett is trying to build a time machine. No kidding. This isn't sci-fi. The basic idea of his time machine is the twisting of space using a circulating light beam. Again, the experiment is based on the Theory of Relativity and yes, the famous equation E = mc². Of course, his work is controversial and remains to be proven. I guess with light being so intricately linked to the very fabric of the universe (very counter intuitive to me), it seems logical that any attempt to manipulate space and time also involves a manipulation of light.

The ancient Jew was onto something when they wrote in in the Bible, ""Let there be light!" They had no idea how insightful that sentence is.

There's a lot more to light than meets the eye, if you know what I mean.



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