Once upon a time, there was an apple. It had three ages.

Read on as we unravel the mysteries of space, time, and gravity, one bite at a time.

One sunny day in 1687, the apple hit an unsuspecting Englishman on his head.  He picked it up. To look at it, it was the same as any other apple. But it got him thinking.

What followed for the apple were its ‘lost’ years.

In 1905, a Swiss office worker picked up the apple, took a bite out of it, and put it down again. In 1915 he picked it up again and ate the rest of it.

This wasn’t an apple involving any mythical talking serpents. It was decades before an Apple – Designed in California, Made in China. It was your standard, everyday, metaphorical apple.

What was so special about this particular apple? (…besides a known life of 228 years)

This apple drove the greatest leap forward in the history of science. It led to new understandings of the nature of the universe. It led to new inventions and innovations that we take for granted today. It gave rise to an understanding of the relationships between space, time and light.

The First Age of the Apple

In 1687 an English mathematician was sitting beneath an Apple tree when an apple fell and hit his head.

In the same situation, we’d rub our head, pick up the apple, and then look up to see where it came from (…an apple tree! What was I expecting to see?)

The mathematician did all these things too, but then took things one step further. Unlike the rest of us, after he looked up into the apple tree he arrived at his Law of Universal Gravitation.

…where every particle attracts other particles with a (gravitational) force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.

Pocketing the apple, Sir Isaac Newton went back inside.

What did the apple do during its ‘lost’ years?

Nothing much, apart from the odd appearances in one of those TV Cooking shows.

It was like a minor celebrity who hit the big time early – without quite knowing how it happened, or what to do next.

It languished for the next 218 years living as an incidental, accidental celebrity.

The accidental inspiration behind Sir Isaac Newton’s Law of Universal Gravitation.

What happened to the apple after that?

The Second Age of the Apple

Meanwhile, in Switzerland, a quiet office clerk was pondering the impact of that apple.

Then one day in 1905, he picked up the apple and took a big, metaphorical bite out of it.

This act gave the apple its second big break in life.

Once again, the apple was an inspiration. It inspired Albert Einstein’s Special Theory of Relativity.

Einstein’s new theory showed that Newton’s gravity wasn’t a force at all.

Gravity was indistinguishable from, or the same thing as, acceleration.

What was ‘special’ about his Special Theory of Relativity?

It only related to special cases where objects are moving with constant speed in a straight line.

What does ‘relativity’ relate to in his Special Theory of Relativity?

Relativity refers to the fact that everything is moving relative to everything else. There’s no fixed frame of reference. Nothing is ever at a standstill. Not even your line at the supermarket checkout.

WTF? you say.

Let’s assume you’re reading this while sitting in a comfortable chair, enjoying a nice cup of tea, or perhaps, eating an apple. Let’s also assume you’re sitting somewhere here on Planet Earth. This is necessary as we all know some people where it doesn’t appear to be the case. While you’re sitting there you are in fact;

• sitting in a chair on planet Earth spinning around at 1,675 km/h – without a seatbelt,
• …while that planet orbits a star – the sun – at 107,000 km/h,
• …while that star orbits the centre of the Milky Way Galaxy at 828,000 km/h,
• …while the Milky Way Galaxy travels through the Universe at Ludicrous Speed – a staggering 2,100,000 km/h.

Now you understand why nothing is ever at a standstill. Everything is moving relative to everything else.

So, mind you don’t spill your tea, let go of your apple, or get up out of your chair too quickly.

What did the Special Theory of Relativity say?

Einstein’s SPECIAL Theory of Relativity contained three BIG ideas.

1) That the laws of physics are the same for everyone.

2) The fact that the speed of light is the same in any situation: This is Space-Time. It’s where events that occur at the same time for one observer could occur at different times for another.

This means that the normal idea of time is wrong. The sequence of events moving from the present, leaving the past behind, as it moves into the future, is wrong.

The “Twins Paradox” is the classic example of this. Assume an astronaut leaves on a 5 year mission at 99.5% of the speed of light. He has a twin brother back on Earth. At the end of the 5-year space mission, the astronaut will be five years older. BUT his stay-at-home twin brother will be 50 years older.

This is Time Dilation. The earth-bound twin’s movement through space-time was only through time. The astronaut-twin’s movement at 99.5% the speed of light was partly through space. So, the astronaut’s movement through time was less than his brother’s on Earth.  In effect, he travelled into the future. The faster you go; the slower time goes – time dilates.

Remember that the next time you notice the supermarket queue next to you moving faster. While you stand still, your annoying former classmate in that queue is ageing slower than you are.

BUT, this isn’t the end of it…

As time slowed down for the astronaut, the straight line he was travelling along in space got shorter. So did his spacecraft.

As the spacecraft moved through space at 99.5% of the speed of light, it was moving through TIME making it shorter. BUT, when TIME and SPACE are the same thing (SPACE-TIME), the spacecraft was also moving through SPACE which also became shorter. Some of the movement was in TIME through SPACE, and some was through SPACE in TIME.

So, back to your idle line in the supermarket while the one next to you is moving faster. Your former classmate in that line is ageing slower than you, AND also appears shorter and slimmer!

Let’s take the SPACE-TIME concept to the dizzy limit. The closer the spacecraft travels towards the speed of light;

• the slower clocks run until at the speed of light, they STOP.
• the shorter the spacecraft measures in a straight line until at the speed of light it DISAPPEARS…

2) This leads on to the equivalence of MASS and ENERGY where at the speed of light, the MASS of the spacecraft becomes INFINITE.

This stops it from going faster than the speed of light.

Why?

Because you’d need INFINITE ENERGY to push INFINITE MASS – which is not possible. (This is where E=Mc2 comes into play). The PHOTONS that make Light have zero MASS. So, their speed (light speed) at ZERO MASS is the universal speed limit.

3)…and finally, that the Speed of Light is;

a) constant; and,

b) independent of the speed of its source; and,

c) independent of the speed of the observer of the light.

Back to our astronaut. What would happen if he were to fire off a laser out in front of his spacecraft while travelling at 99.5% the speed of light?

It wouldn’t creep away from the spacecraft.

The light would behave the same as if the spacecraft were stationary, or even going backwards.

The speed of the source doesn’t matter.

The speed of light is independent of its source and its speed.

So, to sum up the Theory of SPECIAL Relativity, it blurred the distinction between SPACE & TIME;

…back on our idle supermarket queue. While the other one moving faster than yours, your former classmate in that queue is;

aging slower than you; and,

appears to be shorter and slimmer than they are ; and,

the flash of light when your queues’ cash register blows its fuse would be visible to both queues at the same time.

Back to the apple.

When Einstein took a bite in the form of his Special Theory of Relativity, he continued to chew on it for ten years.

It troubled him that it was only a ‘special’ theory.

It only considered the effects of relativity to an observer moving at a constant speed. 

Einstein was the first to admit that it wasn’t how things happened in the real world.

Even your supermarket queue will move at different speeds. It will depend upon the different number of items the people in front are buying.

The same thought (…ok, not that one) occurred to Einstein – that bodies change their speed with time.

This is how the ‘generalised’ came into being. It considered how someone would see someone else who’s accelerating relative to them.

The Third Age of the Apple

What did the General Theory of Relativity say?

Einstein’s General Theory of Relativity contained several BIG ideas. Ideas that built upon his Theory of SPECIAL Relativity.

What was ‘general’ about his General Theory of Relativity?

It was general because it was generalised to include acceleration.

This gave the theory an understanding of GRAVITY.

In his ‘special’ theory, Space-Time was ‘flat’.

In his ‘general’ theory, Space-Time became ‘curved’.

What did the General Theory of Relativity say?

Einstein’s General Theory of Relativity contained one BIG new idea.

…gravity warps space-time around massive objects. The stronger the gravity, the more space-time warps.

GRAVITY WARPING MOTION THROUGH SPACE

An example.

Let’s pretend we have a trampoline in the lounge room.

Let’s call the trampoline Space-Time.

Now, let’s rummage around behind the back of the lounge to find the following;

• a long ruler,
• a piece of chalk,
• a marble,
• a bowling ball,
• …and an old cannonball. (…who left that there?).

Using the chalk, mark the trampoline’s centre with an X.

Taking the long ruler and chalk, rule a line across the trampoline – not across the centre, but a little off-centre.

Now take a marble and place it on X in the centre of the trampoline. Notice that the line doesn’t change its shape.

Take the marble away and replace it with the bowling ball. Notice that the bowling ball sinks into the trampoline and that the line changes its shape and bends.

Now replace the bowling ball with the cannonball. Notice that the cannonball sinks even further than the bowling ball and that the line bends even more.

The cannonball has more MASS than the bowling ball which has more MASS than the marble.

As the MASS put on the X increased from the marble to the bowling ball to the cannonball, the line’s curve increased. The greater the MASS, the greater the CURVE.

The curving line is the curving of SPACE-TIME caused by the large MASS of the object. The larger the MASS, the larger the pull of GRAVITY toward it. A deeper GRAVITY well forms with each ball of greater MASS.

GRAVITY WARPING MOTION THROUGH TIME

The curving chalk line can represent the bending of the path of a planet or the bending of light.

The larger the MASS, the stronger the pull of GRAVITY. The greater the GRAVITY, the deeper the gravity well.

The deeper the gravity well, the SLOWER TIME runs the CLOSER you are to it. This GRAVITATIONAL TIME DILATION.

Back to our annoying former classmate in the faster-moving supermarket queue. Remember? The one who was ageing slower than you. As it turns out, she lives on the ground floor of her apartment block. Your apartment is on the 25th floor. Once she gets home from the supermarket, she is still ageing slower than you. Why? Because she is closer to Earth where she feels a greater pull of GRAVITY than you – her gravity well is deeper. The effect? TIME for her passes more SLOWLY. Why? Because SPACE-TIME has curved more/deeper for her than you and has further to travel.

The key here is that GRAVITY isn’t a force. It is the result of our surroundings accelerating relative to us.

Relative to us, the earth exerts a ‘MASS-ive’ pull we feel as GRAVITY. We feel it because the ground stops our ACCELERATION towards the centre of the Earth’s MASS. This ACCELERATION towards the earth’s centre is what we feel as GRAVITY. It’s what stops us from falling ‘up’ into space.

So, what does this mean?

The MASS of MATTER curves SPACE-TIME.

The scattering of MASS through the universe determines the CURVATURE of SPACE-TIME.

The CURVATURE of SPACE-TIME then determines the scattering of the MASS of MATTER.

This is a FEEDBACK LOOP where one thing drives the other, and vice versa.

MASS determines the geometry of SPACE-TIME.

The geometry of SPACE-TIME determines the motion of MASS.

 

Let’s bring things a little closer to home.

The centre of the MILKY WAY galaxy curves SPACE-TIME for the SUN.

The SUN curves the SPACE-TIME for the Earth which curves SPACE-TIME for the Moon.

The FEEDBACK LOOP stops objects from drifting off into the Universe in straight lines.

The MASS of the larger objects warps SPACE-TIME around them.

The gravity wells change the paths from straight to curved lines.

Curving SPACE-TIME also curves LIGHT since it travels through SPACE-TIME.

The MASS of a nearby object drags the photons that make up light off its straight-line path.

What has been its legacy?

The theory has expanded our understanding of the universe, its expansion, the presence of black holes, and the effect of gravity on time. The most commonplace legacy is that it gave birth to an App in a new type of Apple. The Global Positioning System (GPS) functionality on your handheld Apple device. Satellites in geo-stationery orbit above the earth enable you to pinpoint your location.

Einstein’s Theory of General Relativity makes this work.

How?

The theory predicted the effect of gravitation on time depending on how close you are to an object’s MASS.

This is the GRAVITATIONAL TIME DILATION effect explained above.

Time isn’t the same RELATIVE between you on the ground and satellites in orbit.

GRAVITATIONAL differences mean time passes slower for the satellites than for you.

This means that the clocks on the satellites need to be adjusted daily.  If they weren’t changed, GPS accuracy would drift by up to 10 kilometres per day.

Do we know all there is to know about it now?

No.

The Theory of General Relativity explains many things.

It even explains things about your former classmate who lives on the ground floor.

But there are still gaps to close.

To explain how everything works in the Universe requires more research and theorising. 

As always, whatever’s discovered in the future will build upon what’s come before it.