Einstein coined the label Spacetime to encapsulate his new concept: that to describe the physical reality of the universe, space and time must be considered together. Either component alone was incomplete. He was successful in compiling a mathematical formulation that could express and predict the observed characteristics of this aspect of physical reality. He called it a Theory of Relativity, because the observed physical characteristics could differ, relative to the way they were observed.

Hera, known as queen of the Greek pantheon of gods, was the first to challenge this notion. Her reality was not captured by this formulation. She existed in the realm of ideas, with no physical reality at all except what she chose for herself. Thus, for her, Einstein's encapsulation of reality was incomplete.

Einstein was well aware of this limitation. But in the opinion of his fellow men it was commonly believed that Hera did not exist. They failed to consider the obvious idea that if she did not exist, then they should not have known of her.

In the early days it was often said that only two people in the world truly understood Einstein's theory of relativity. It eventually turned out that Einstein wasn't one of them. He understood the basic physics, but he was not enough of a mathematician to understand all of the implications of the theory he had devised. It was left to the much younger Belgian Mathematician, Scientist, and Catholic priest Georges Lemaitre to explore them. 

In line with the accepted thinking at the time that the universe was eternal and unchanging, in 1917 Einstein had proposed a static model for the universe, and supposed that his Spacetime would be infinite in extent. Ten years later, Lemaitre's analysis of Einstein's mathematics led him to the conclusion that Einstein's universe should be not static, but expanding. 

In 1929, Edwin Hubble's astronomical observations led him to the discovery that the universe was indeed expanding, at a rate that came to be known as the Hubble Constant. With this supporting evidence, Lemaitre's 1927 paper was published in English in 1931.  In line with this evidence, Lemaitre understood that if the universe was expanding at a constant rate, at some earlier time it must have been much smaller. He called his predicted earliest state the "primeval atom". Now we call it the Big Bang.

Einstein's Theory of Relativity has two prominent features. One is that the speed of light is constant. The other is that gravity is not a force acting across the distance between objects, but a shape of space acting locally upon objects in the same vicinity. 

The first of these features means that no matter where an object is in the spacetime universe, or how fast the object is moving, light in its vicinity will always be observed to be moving at the same speed, its own special speed (in empty space that's about 300 million meters per second).

This formulation required that light would have no rest mass, and when moving would have mass equivalent to its energy (by the famous equation that says energy equals mass multiplied by the speed of light twice: E = m x c  x c ). Any ordinary object that had mass when not moving would require additional energy to move relative to its surroundings. The formula for this said that it would require infinite energy to accelerate such an object to the speed of light. Thus light speed became the absolute limit for the speed of any object in space.

The other feature of the theory said that the shape of a gravitational field conforms to the presence of mass, in such a way that freely moving objects respond to the shape of the field, and their motions are guided by it. It is the resulting shape of space that causes planets to orbit around a star, and moons around a planet.

As noted above, all of this was inspired by Einstein's efforts to compile a mathematical formulation that could express and predict the observed characteristics of physical reality. None of it addressed Hera's complaint.

Meanwhile, another of Einstein's observations had inspired investigations into the notion that light arrives in little packages. This idea led to what became known as Quantum Theory. Here efforts were addressed not to the entire physical universe, but to its smallest parts. 

The first to make real progress in describing this quantum realm was the Danish physicist Niels Bohr, who began the development of a useful model of an atom. Atoms had previously been pictured as tiny particles orbiting other tiny particles like planets around a sun. The interactions of these particles were ascribed not to gravity, which was much too weak to have any detectable effect at this scale, but to electrical energy in the form of discrete electrical charges. The little electron planets had to be negatively charged and the bigger proton suns had to be positively charged, so they would be attracted to each other.  

Einstein's work had already shown that electromagnetic energy arrived as photons in little packets (now called quanta). Bohr's contribution was to suggest that the energy in these quantum packets determined the size of the electron orbits.

These ideas caused quite a stir, because by this time there was already a very successful theory of light (and indeed of electromagnetic energy in general) that said that it came in waves. Suddenly deciding to call these waves "packets" didn't seem to make sense.

Bohr said it didn't have to make sense. It was simply a mathematical idea. If it predicted what was actually observed, then it was useful.

After many years of inspired efforts by many people, it was accepted that both the wave idea and the particle idea were right, and both behaviors could be observed.  Which behavior would be observed depended on how the observations were made.

Not many people noticed that this conclusion made Queen Hera happy. She already knew that what people called physical reality was based on ideas, not the other way around.

Testing Bohr's ideas experimentally gave hint after hint that refinements in quantum theory were needed. So refinements were made. Too many to recount in detail here. Electrons needed additional features to account for the ways magnetic fields affected their behavior. Protons were even more complicated. More theory was needed. The best idea for that seemed to be that protons were made of smaller particles. These got named quarks.

This proliferation of particles did not make Einstein happy. For one thing, his mathematics was the kind that allowed quantities to have any value. The idea of there being all these fundamental particles that were expected to have set values didn't fit well with his way of thinking. And there seemed to be overwhelming evidence that Relativity was right. At least at a scale where gravity could be measured.

At the same time, the math being developed for quantum theory didn't work nearly that well. It seemed that endless experiments were needed to pin down a defining value for each new particle. There was also the idea of quantum jumps, that a particle was allowed to be in one place or another place, but not in any place between. This seemed to imply that particles could exceed the speed of light, that these jumps actually took no time at all to happen. Clearly not compatible with one of the most basic ideas of Relativity. 

Here another German physicist came to the rescue, His name was Werner Heisenberg, and in 1927 he pointed out that in the quantum realm you can measure ether the position of a particle, or its speed, but not both, because the action of measuring one will always change the other. This was called the Uncertainty Principle. It helped ease Einstein's own uncertainty, because it gave everything a sort of wavy nature. 

Hera liked it too, because it showed that reality depended on choices between different ideas.

Then there was Planck's Constant. Einstein knew all about this, because it was Max Planck's discovery that had led him to the idea of particles of light, photons. Einstein didn't like to call them particles. He preferred to call them packets. Wave packets. Photons weren't like all these new particles that seemed to have a single defining value. A photon could have any value, because light could have any color, any wave length, any frequency. Red light waves had a lower frequency than blue light waves. So a red light photon had less energy than a blue light photon.

Planck's Constant is found in a very simple equation, E = hf, where E is energy, f  is frequency, and h is Planck's Constant. This equation says you can tell the energy of a photon by multiplying its frequency by h. It explained why light couldn't have infinite energy, because packets with more energy were harder to make, so there wouldn't be as many of them.

The value of h is very small. From the above its value h = E/f. What this means is that when photon energy E goes up, electromagnetic frequency f  goes up equally. As an example, red photons of light carry about 1.8 electron volts (eV) of energy, while each blue photon transmits about 3.1 eV. Red light has a frequency of about 430,000 hertz, while blue light has a frequency of about 750,000 hertz. 

The perhaps unfamiliar energy unit called electron volt is very small, but useful when referring to things on the atomic scale. Its unit value, written as grams of mass divided by the square of centimeters per second, works out to E = (1.602 gram x cm/second x cm/second) all divided by a 1 followed by 12 zeros, or roughly 1.6/1,000,000,000,000. In other words, one trillionth of 1.6. An extremely tiny amount of electromagnetic energy is found in a typical photon.

When the even tinier influence of gravitational energy is taken into account, a number called the Planck Length is arrived at, which turns out to be about 1.6 divided by 1 followed by 35 zeros. An unimaginably tiny distance. 

It is at this scale that what has been called the Quantum Foam is encountered. Hera might tell us that at this scale the physical realm is not yet real, and only the realm of new ideas remains.

It is in this realm that Quantum Field Theory holds sway. It is the realm of the possible, at the edge of time. It is the realm where, from what is possible, those events which are most probable will be selected and made real. 

This is the realm of the origin of dreams. It is the realm of chaos, the infinite realm of unlinked events. It is space without time. It is the realm of Raven.

It is here on the edge of time that dreams become entanglements, the linked events we think of as reality. It is here that memories are born, time becomes fixed. It is the realm of Eagle.

Einstein's Spacetime is the physical universe. It is the sum of memories of past events in dream space. It is history. Einstein was an epitome of Eagle. He opened up possibilities for a new future by expressing a new understanding of the past. Spacetime is a product of the Eagle impulse to bring order to idea space, to dream space.

Eagle brings order by giving events the ability to form entanglements, interactions that link them to other events. Events tend to link by similarities in their prior entanglements. These linkages then become chains of related events. They endure as memories, and they grow by accreting additional events. 

We must assume that each original individual event in the nascent universe of ideas was a potential point of origin of a chain of events. Each such individual then grew by the process of forming links and further entanglements with other events. 

As a result, we each now have a universe that comprises not just a space defined by a collection of unconnected events, but a space within which events have been linked in sequences that we call time. Each of us is witness to our own sequence of events. Each of us has a fixed Past we can look back on, a present Now from which we contemplate both past events and future possibilities, and the ability to choose from among those possibilities our own next Now. We each have our own evolving spacetime universe. We can imagine, along with Einstein, that taken altogether they comprise a Spacetime that contains us all.