THE LONG READ : Musings About The Universe – From Einstein’s General Relativity to Current Observations of Uniformity, Expansion and Dark Energy

This post is based on the first chapter of the book “The Hidden Reality” by Brian Greene, which I’m currently reading and recent discoveries about our universe that I found online.

I suggest you read this slowly and with patience and also refer the links I have provided.

So I picked up “The Hidden Reality” a couple of days ago and the first chapter has got me hooked already! I’m taking my time on this one to understand all the concepts in detail.

Let’s start with a story…

Einstein’s General Relativity

Albert Einstein and Geroges Lemaitre

“Your mathematics is correct but your physics is abominable”,  it was 1927 and Albert Einstein reacted this way to Belgian, Georges Lemaitre’s presentation. Lemaitre informed Einstein that his work on General Relativity had lead to a dramatic rewriting of the story of creation.

Lemaitre who would later be known as the ‘Father Of The Big Bang’ put forth a theory in which  the universe began as a tiny speck of astounding density called the ‘Primeval Atom’ which expanded and swelled over vastness of time into our cosmos.

Einstein rejected these claims. It wasn’t the first time someone was putting this idea to him. In 1921, Alexander Friedmann came up with multiple solutions to Einstein’s equations in which space would stretch, causing the universe to expand.

Einstein balked at this.

Einstein was wrong and he would retract later.

Einstein was brilliant no doubt but he refused to be mathematics’ pawn. He bucked the equations in favour of his intuition about how the cosmos ‘should‘ be. His deep seated belief that the universe was fixed and unchanging could not be simply replaced by Lemaitre’s expanding universe.

Einstein had breathed new life into spacetime. He proved that space and time both curve(known as spacetime curvature). He proved that warps in space and time don’t need a facilitator since they ‘are’ gravity. Space is three dimensional so when it warps, it warps all around an object not just underneath it. Before Einstein, gravity was a mysterious force that one body somehow exerted across space on another. After Einstein, gravity was recognized as a distortion of environment caused by one object and guiding the motion of others.

Einstein spent years developing this idea into rigorous mathematical framework and the resulting Einstein Field Equations, the heart of his general theory of relativity, tell us precisely how space and time will curve as a result of a given quantity of matter(More precisely matter and energy; E=mc^2). This theory then shows how such spacetime curvature affects the motion of anything – a star, a planet, comet or light itself – moving through it. This helps physicists to make detailed predictions of cosmic motion.

Evidence to support it came quickly, in 1915 Einstein used his equations to calculate Mercury’s trajectory and explain it. Then, in 1919 Arthur Eddington and his collaborators showed that distant startlight passing by the sun on it’s way to earth followed a curved path, just like general relativity had predicted.

Einstein was heralded as the world’s newfound scientific genius.

In 2003, the Cassini-Huygens spacecraft(which was used for studying the trajectory of radiowaves that passed near the sun) showed that the curved spacetime model was in fact correct.

This theory has truly come of age now because the GPS systems that we carry in our pockets in our smartphones communicate with satellites whose internal timing devices rountinely take account of the spacetime curvature they experience from their orbit above the earth. If satellites didn’t do this we would get inaccurate showing of our positions.

What started out as a set of equations in 1916 are now in our pockets! Haha 🙂



A Uniform Universe

Consider this perspective, if you look at a cup of tea in the microscopic level, you’ll find some water (H2O) molecules here, some empty pace some tea molecules over there, more empty space and so on. But from the macroscopic scales, the cup of tea is uniform. Einstein believed that the universe was like that cup of tea. The variations we observe – earth here, some empty space, the moon, more empty space then other planets, more space and the sun – are all small scale inhomogeneities. He suggested that on cosmological scales these variations could be ignored because like the cup of tea they would average out and appear uniform.

He called it the cosmological principle.

In Einstein’s day evidence to support this principle was not possible. However today we have proof of this.

Here is the link.

Most cosmologists use Einstein’s cosmological principle : that if we look on sufficiently large scales, the universe is actually uniform. The vast majority of calculations made about our universe start with this assumption: that the universe is broadly the same, whatever your position and in whichever direction you look.

The scientists from University College London and Imperial College London have put this assumption through its most stringent test yet and found only a 1 in 121,000 chance that the universe is not the same in all directions.

They used maps of the cosmic wave background (CMB) radiation: the oldest light in the universe created shortly after the Big Bang. The maps were produced using measurements of the CMB taken between 2009 and 2013 by the European Space Agency’s Planck satellite, providing a picture of the intensity and, for the first time, polarisation (in essence, the orientation) of the CMB across the whole sky.

Dr. Stephen Feeney said: “This work is important because it tests one of the fundamental assumptions on which almost all cosmological calculations are based: that the universe is the same in every direction. If this assumption is wrong, and our universe spins or stretches in one direction more than another, we’d have to rethink our basic picture of the universe.

“We have put this assumption to its most exacting examination yet, testing for a huge variety of spinning and stretching universes that have never been considered before. When we compare these predictions to the Planck satellite’s latest measurements, we find overwhelming evidence that the universe is the same in all directions.”

Lead author Daniela Saadeh from University College London added: “You can never rule it out completely, but we now calculate the odds that the universe prefers one direction over another at just 1 in 121,000. We’re very glad that our work vindicates what most cosmologists assume. For now, cosmology is safe.”


Our Universe Is Expanding

However, Einstein while studying his equations again, found something unexpected and, to him, unacceptable. The main scientific and philosophical stance was not only that on the largest of scales the universe was uniform, but that it was also unchanging. But the math showed that the density of matter and energy cannot be constant put through time. Either the density grows or it diminishes, but can’t stay put.

Einstein recoiled. According to the math the universe on the grandest of scales would be changing. The eternal static cosmos that Einstein expected emerged from his equations as simply not there.

On the third line of the general relativity a particular intrinsic feature of spacetime relevant for gravity i.e the amount of energy stitched into the very fabric of space itself. Just as every cubic meter of water contains a certain amount of energy, every cubic meter of space contains energy as well, summarized on a number on the third line.

He took a good look at that third line and when general relativity wasn’t adhering to a static universe, Einstein changed the mathematics. If instead of a zero he entered a positive number endowing spatial energy as a positive value. Every region of space would push away from each other, producing what most physicists thought impossible : repulsive gravity!

He found that if he precisely adjusted the number, the repulsive gravitational force produced across the universe would exactly balance the usual attractive gravitaional force generated by matter inhabiting space – giving rise to a static universe. He called this the cosmological constant.

And it best described what he and others expected about the uniform, unchanging universe.

Imagine an infinite flat rubber surface(the universe) stretching in all directions, then if you sprinkle glitter on it (the planets, galaxies and stars). Then you would find that the more it stretches the more the glitter particles move away from each other.

Coming back to 1927, Lemaitre approached Einstein with his result that general realtivity gave rise to a new cosmological paradigm in which space would expand. However after changing the mathematics and dismissing Friedmann’s similar claims Einstein had little patience for this.

But then in 1929, using the world’s largest telescope, American astronomer Edwin Hubble gathered evidence that the distant galaxies were all rushing away from the milky way!
The photons that Hubble examined traveled back to earth with a clear message – The Universe is not static! It is in fact expanding!

Einstein’s reason for introducing the cosmological constant was unfounded. The big bang model that described the universe as a cosmos that began enormously compressed and continously expanding has from then on become widely heralded as the scientific story of creation. Put forth by Lemaitre and Freidmann – they were finally vindicated. While Einstein was left wishing that he never meddled with the third line.

It has been proved that our universe is expanding. Most recently though we have found out that it’s expanding at a faster speed than imagined before!

Here is the link

The universe is expanding faster than anyone had previously measured or calculated from theory. Nasa and the European Space Agency jointly announced the universe is expanding 5% to 9% faster than predicted, a finding they reached after using the Hubble space telescope to measure the distance to stars in 19 galaxies beyond the Milky Way.


Dark Matter And Dark Energy Depiction

The mathematics showed that the so called critical density contained “just the right amount of matter”(Critical density = 2 x 10^-29 grams per cubic centimeter) or about six hydrogen atoms per cubic centimeter .

But In 1998, something remarkable happened. Through some observations and a chain of reasoning astronomers realized that they had been leaving out an essential component out of the tally of average density(They had observed that the average density of space was on the low side about 27 percent of the critical density which was about only two hydrogen atoms per cubic centimeter)

They found or rather observed a diffuse energy that appeared to be spread uniformly throughout space. The data shocked everybody! There was an energy suffusing space. Which sounded a lot like the cosmological constant that Einstein had theorized and then retracted eight decades later. Could have modern observations resurrected the comsomlogical constant from the dead?

Nobody knows for sure. Scientists have come up with a name for this diffuse energy as “Dark Energy” because the energy does not give off light.

“Dark” also describes the many gaps in understanding. Nobody can explain the dark energy’s origin, fundamental composition, or detailed properties.

But what is even more remarkable is that the measurements of dark energy in space, made so far contributes to approximately 73 percent of the critical density. Which when added to the 27 percent already measured (as mentioned above) brings the total critical density up to 100 per cent just the right amount for a universe with zero curvature. Much like the infinite rubber flat rubber table.

Here is some insight…

Here is the definition of Dark Energy :
In physical cosmology and astronomy, Dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.

Here is definition of Dark Matter:
Dark matter is an unidentified type of matter comprising approximately 27% of the mass and energy in the observable universe that is not accounted for by dark energy, baryonic matter (ordinary matter), and neutrinos.The name refers to the fact that it does not emit or interact with electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum.Although dark matter has not been directly observed, its existence and properties are inferred from its gravitational effects such as the motions of visible matter, gravitational lensing, its influence on the universe’s large-scale structure, and its effects in the cosmic microwave background. Dark matter is transparent to electromagnetic radiation and/or is so dense and small that it fails to absorb or emit enough radiation to be detectable with current imaging technology.

This is the latest on Dark Energy and Dark Matter

This one is as latest as today

This one is by NASA

While here is the tag on this physics website

And another

It’s got links to the worlds newest and most sensitive dark matter observing machine  as well as an explanation of dwarf galaxies through dark matter and an observation of massive holes punched through a trail of stars by dark matter. Read them up if you are interested.


I have summarized what I have read so far in Brian Greene’s book. It’s only the first part of the first chapter and much before he goes into the details of parallel universes and so on.
It is very interesting that so much has been accomplished in terms of space exploration but yet we have only a fraction of knowledge about our universe. What we are going to find in the future is certainly exciting and I hope we make ground breaking revelations and discoveries.

However, the mystery about Dark Matter and Dark Energy continue. I will try to post what I find about it in the future.

I hope you have kept an open mind about all of this stuff that I’ve explained because that’s how thinking should be.

I leave you with a small quote

“To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.”
– Albert Einstein

Cheers all!

Peace 🙂

Have a great sunday!


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