Gravity

Published on by Catherine Toulsaly

Lunar eclipse over Lake Maggiore

Lunar eclipse over Lake Maggiore

There are concepts related to emergence, information and gravity, and properties like colors that point to a sense of universality. As the full Moon passed through the shadow of Earth it appeared orange, reminding me of fall colors when the weather turns cold. The same orange glow seems to radiate through the cosmic microwave background (CMB) that was formed about 380,000 years after the Big Bang.  As the universe cooled down, the symmetry between the different species of elementary particle broke in a phase transition analogous to the freezing of water.

 

The answer to the following question eludes me: if we experience the expansion of the Universe, what is beyond our Universe that allows it to expand? It is not the question that matters but the way you formulate it.  A scientist who would attempt to use quantum mechanics in theoretical cosmology might rephrase the unsolved problem this way:

...the nature of the accelerating expansion is seeking to answer one or the other question: “Does nothing weigh something?” or “Is nowhere somewhere?”

Eric V. Linder

According to Erik Verlinde’s paper “On the Origin of Gravity and the Laws of Newton”, what defines the expansion - that is gravity and space-time geometry - is emergent. And so if gravity is emergent, when and how did it emerge? Verlinde adds that gravity could emerge from a microscopic description that doesn’t know about its existence and that the link between the universe without gravity and the universe with gravity is information  “measured in terms of entropy”. As Carlo Rovelli wrote in his book The Order of Time (Riverhead books, 2018, p.34), entropy is “nothing other than the number of microscopic states that our blurred vision of the world fails to distinguish” and depends on the peculiar coupling between us and the rest of the universe. In the context of the uncertainties that we face as observers when we attempt to measure the true value of past and future events, the increase of entropy stems from our own assessment and prediction of what matter will become in macroscopic observables. Rovelli specifies that for any time evolution, there is a split of the system into subsystems such that the initial state has zero entropy and then entropy grows.  

Cosmic microwave background seen by Planck

Cosmic microwave background seen by Planck

The cosmic microwave background (CMB) looks like a patchwork of colors guiding us into the past and the future, a thermal map from which we aim to deduce distances in time and space. The CMB gives a unique perspective on the patterns of distribution,  how tightly matter was clustered throughout the young Universe and how fast it is fragmenting and reorganizing. Its growth evolution seems to hint at a nonexisting phenomenon whose resulting dynamics we observe. In the discussion on gravity, two discoveries help create in my head an image of a time-space geometry. My mind drives through an interconnected system of one-way streets from ideas to images and from concepts to visual representations. Those mental images foster an internal dialogue that helps me to enter a new level of consciousness as I visualize new ideas and concepts.

 

First, the discovery of a 13.5 billion-year-old low-mass star,  the most metal-poor star ever  to be observed, located about 20 000 light-years away in a binary system, would place it about at the time when the CMB was imprinted. Second, the farthest individual star ever to be seen, a blue supergiant star named Icarus would have been just a flicker if it had not been for the magnifying effect of gravitational lens. Since its light has taken 9 billion years to reach Earth, it appeared to us as it was when the universe was about 4-5 billion years old, at the time of the earliest form of life on Earth perhaps hidden inside the fissure of a rock, potentially, along with billions of other specks of life spread across the Universe escaping slowly from their rocky cradle. Icarus is long gone but its existence has reached our consciousness only today. I visualize in my mind the depth of the spatial layout and struggle to add the factor time in the equation.  I wonder what the biosignature of our young Universe was like then and imagine billions of microorganisms feeling for the first time the soft push and pull of gravity. Is life still hidden today in a lunar rock, on Mars, Venus or on an exoplanet waiting to escape?  

 

The Webb Space Telescope, scheduled to be in orbit in 2021 at more than 1 million miles from the Earth, will have the capacity to detect faraway stars like Icarus. Equipped with 18 mirrors in beryllium, it will be operational six months after its launch and will be able to look far back in time and capture light from Population III stars, like the 13.5 billion-year-old star, composed exclusively of hydrogen, helium, and a dusting of lithium.

 

Gravity shows its power of attraction when matter is able to cluster. Gravitational lensing occurs when gravity causes the light to bend. Gravitational waves ripple when gravity travels at the speed of light. Gravity is not the same everywhere and depends on one’s location. The astronauts on the moon would feel just about one-sixth of the level of gravity felt on Earth. Are spacetime and gravity intertwined? Gravity is an entropic force that emerges with the increase of entropy. Since the emergence of gravity does not derive from the properties of the underlying microscopic “universe”, what precedes gravity is a quantum gravity that is holographic. Holographic projection acts as a translation tool enabling information to be stored and passed on to another set of dimensions. Holographic models for the very early universe  may explain the data embedded in the cosmic microwave background and are competitive to the standard model of Big Bang cosmology.

As I dissect every word, I struggle to wrap my mind around the idea that space emerges together with gravity. I imagine the Universe being a multi-dimensional race track where we, observers, are at the finish line. And all the planets and stars are racing to send us a signal. Some, faster than others, reach our consciousness.

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