There is something both calming and therapeutic about looking up at the night sky and even though the milky way makes for a stunning view of the heavens its easy to forget that what we can see with the naked eye is an incredibly tiny, tiny fraction of the Universe and we need tools like the Hubble space telescope to see to the farthest objects.
When it comes to the vastness of space and the massive scales involved, it’s difficult to imagine not only the distances involved but also the time it takes light to travel across them compared to our everyday human-scale lives.
And as large as the scale of the space is its only half the story. We exist somewhere near the middle between the very large and the very small where there is an even greater range of scale going down to the very smallest unit of measurement we can currently practically use, a distance so small that is if a meter were scaled down to that size, the entire observable universe would be just a bit larger than an atom. This is a very simplified look at the scale of everything, the big the small and the paradox that exists at the very bottom.
As they say, go big or go home, so we will start with the size of the entire observable universe. Our best guess based on observations and allowing for the expansion of the universe since the big bang is that it’s about 93 billion light-years across, about 8.8×1023 Km with the distance from the edge of the observable universe in any direction to us being 46.5 billion lightyears and here we come across a unit of measurement which tries to make things easier to comprehend, the light-year, or how far the light will travel in one year.
One lightyear is the equivalent to 9.46 trillion km, still not an easy distance to comfortable conceive but for some sort of comparison the fastest spacecraft we have yet launched, the Parker Solar probe which will observe and fly through the upper part of the Sun’s atmosphere in 2024 will reach a maximum speed of 690,000 km/h by using seven gravity assists on it’s way to the Sun.
The parker could fly the 5566km from London to New York in 29 seconds and yet It would take the Parker probe 1,565 years to travel one light-year, that’s just 0.064% the speed of light. Our nearest star Alpha Centauri is 4.3 lightyears away, a one way journey time of 6729 years for the Parker.
If we cloned the earth and placed these copies side by side to the edge of the known universe we would have to make 34,300,000 trillion copies.
The farthest galaxy we have seen so far, GN-z11 is approximately 32 billion light-years away or 1023 km, its also the oldest at 13.4 billion years. If we tried to send a probe like the Parker to GN-z11, it would take just over 50 trillion years to get there and that’s assuming that the expansion rate of the universe was to be zero for its entire journey, that’s 3228 times the age of the universe to date.
But in reality, it would never get there because the rate of the expansion of the universe is accelerating far faster than our probe could ever fly, a bit like a sprinter trying to catch up with a plane.
There must also be some distance farther out than the observable edge but how much farther we just don’t know, some suggest it could be up to 250 cosmic horizons farther out though we will probably never know where the edge of the universe is because the light from there has not and might never reach us.
So lets scale back a bit to largest thing in the universe, the Hercules-Corona Borealis Great Wall, a galactic filament made up of billions of galaxies bound together by gravity that is about 10 billion light-years across and also about 10 billion light-years away from us.
It’s now thought the could to be about 2 trillion galaxies in the observable universe, many are small and contain just a few of 10s of thousands of stars but some are very large galaxies like our own Milkyway with 200 billion stars and others with many more.
These 2 trillion galaxies aren’t evenly scattered around the universe, they are clumped together by gravity into local clusters, which then create superclusters which then makeup huge filaments like the Great Wall.
There are thought to be about 200 billion stars in our galaxy the Milkyway, and as far as galaxies go it’s pretty big at about 100,000 light-years across or about 946,000 trillion km but our nearest galactic neighbour the Andromeda galaxy which 2 million light-years away is about 220,000 lightyears wide and is thought to have up to 1 trillion stars making it the largest in our local group of galaxies.
Big as Andromeda may be, there are even bigger galaxies out there, Malin 1 is a low surface brightness spiral galaxy and the biggest spiral type yet found at 640,000 lightyears across and 1.19 billion light-years away from us.
However, one the biggest Galaxies yet found is IC 1101, a supergiant elliptical galaxy with the diameter of its halo stretching over 4 million lightyears. It estimated to contain 100 trillion stars and at its centre there is bright radio source which thought to be a ultra-massive black hole in the mass range of 40 to 100 billion solar masses, making it one of the largest known black holes in the universe.
For all the galaxies and stars, black holes and other cosmic stuff out there, space, in general, is a very empty place. The interstellar void between galaxies is an almost perfect vacuum and much better than any we can make here on Earth. The stuff out there mostly single atoms of hydrogen, helium, dust particles and metals expelled from supernovas but here matter can be so thinly spread out that it’s density can be as low as 0.1 atoms per cubic centimetre of space. Even in the space at the centre of galaxies, it’s only about 1000 atoms per cubic centimetre.
In fact when the Andromeda and Milky way galaxies collide in about four billion years its highly unlikely that any of stars in either galaxy will hit another star. The space between the stars is far, far greater than the stars themselves. So whilst their orbits will be flung around by the collective effect of gravity, the stars and any planets they may have will just glide past each other at still enormous distances.
Stars also vary greatly in size with the vast majority of them in a milky way being red dwarfs, the smallest and coolest stars in the main sequence. The smallest of these having the mass and size of about 8% of our sun and a surface temperature around 2000 Kelvin. Because they are so cool and small they very difficult to see beyond 300 light-years with our current technology.
Of the 60 closest stars to our sun, 50 are red dwarfs. Because they are small slow burners of their hydrogen fuel, their life spans will be measured in the trillions of years.
At the other end of the scale are the red hypergiants like UY Sucti, currently the largest known star which is 1700 times our Sun with a diameter of 2.3 billion km meters but only 30 times its mass of our sun. If you placed it where our sun is, it’s outer edge would engulf the orbit of Jupiter.
But in the very early universe, there was far more hydrogen in much denser clouds from which the first stars formed.
This allowed massive blue giant stars of up to 1000 solar masses or more to exist but they also had very short lives of maybe just a million years or so before collapsing into supernovas and exploding out some of the heavier elements that went on to make planets like earth and eventually us. By the time our Sun was forming there could have been well over a thousand generations of these massive stars to seed the universe with heavier elements.
But Even our sun which a very average star, is on a massive scale compared to the earth. Its diameter is 1.39 million km or 1.39 x109 meters. An average sunspot which appears like dot on its surface could easily swallow the earth with room to spare and you could fit a million earth’s inside the Sun’s interior.
Even some of our local planets are on scales which are huge. Jupiters diameter of 140,000 km is larger than the smallest star yet found and its largest storm system the Red Spot which has been raging for over 340 years is 1.3 times the size of Earth.
On Mars, Olympus Mons, the tallest volcanic mountain in the solar system is two and half times the height of Everest and the mariner Valley is the largest canyon in the solar system that stretches over 3000 km and over 8km deep in places, you could lose our grand canyon in one of its side channels.
And so we reach human scale, 1 meter. But we are not just one entity, the average human consists of about 30 trillion cells all working together. Each one containing a strand of DNA consisting of 3.2 billion bases pairs coiled around itself to form a double helix which is such an impressive piece of packaging that if you straightened it out it would be about 2 metres long, yet coiled up its just 6 microns across, a micron being a thousandth of a millimetre or 10-6 meters.
Small as it may be if you took all the DNA in your body, stretched it out and joined it end to end it would be over 60 billion km long, enough to reach from earth to Neptune and back about 7 times.
But life gets smaller, Mycoplasma genitalium is a parasitic bacterium that lives in the bladder and waste disposal organs of primates and is the smallest to be capable of independent growth and reproduction and is about 2-300 nanometers in length, over ten times smaller than the coiled DNA.
Viruses take this a stage further by dumping the need for a cell body altogether and instead hi-jack other cells to make copies of themselves. Viruses are the smallest living thing though technically they aren’t alive as they can not reproduce without a host cell to do the work for them and although their size is around 2x 10-7 or 20 nanometers across there are thought to be at least 1031 individual viruses particles on earth, more than there are stars in the known universe by about 100 million times and if lined them up end to end they would stretch out 100 million light-years.
Moving down through molecules to atoms we reach what was thought to be the smallest building blocks of matter at 10-10 meters. Most atoms are between 30 and 300 picometers but the nucleus of an atom is 10,000 times smaller in the range of 1-10 femtometers or 10-15 metres.
The nucleus of the atom is made up of protons and neutrons except for hydrogen which has no neutrons. Protons and neutrons are made of smaller fundamental particles called quarks, leptons, gauge bosons and the Higgs boson.
Here we’re getting down 10-20 meters and you would think that we had reached the end of our measurement scale but no, there another 15 orders of magnitude to go before we reach the Planck length.
At these scales, matter is described by quantum mechanics and becomes so strange that the physicist Richard Feynman said “If you think you understand quantum mechanics, you don’t understand quantum mechanics.”
Particles here are best thought of as excited states or quanta of underlaying quantum fields and are at the very limits of our knowledge where you can never know the exact position of a quantum object, they can be waves or particles and randomly pop into and out of existence for a few billionths of a second.
But what of the Plank length and is it the smallest distance there is?. Well, basically it was conceived by Max Planck as an absolute frame of reference based on natural physical constraints rather than an arbitrary human-made measurement system like feet, inches, centimetres & meters.
The plank length is 1.6 x 10-35 meters. To imagine this think of a dot that has the same diameter as a human hair, about 0.1 mm, this is about the smallest thing we can see unaided. If that 0.1mm dot were magnified to the size of the observable universe, all 93 billion light-years of it, then the Planck length would be the size of a 0.1mm dot in comparison.
Down at this scale and smaller, we are into the so-called quantum foam where chaos reigns. The Plank length also marks the limit at which quantum gravity begins to have an effect and the laws of physics as we know them still work. Anything smaller than this is where our theories of spacetime and general relativity as created by Einstien breakdown and become unworkable.
This is also why we don’t know what happens in black holes because they would be at these and maybe smaller scales internally.
If we tried to measure anything the size of the Planck length such as the strings in string theory, the photon speed needed would be so high that the amount of energy required in such a small space would create a microscopic black hole and the more energy you put in the bigger the black hole would become.
So, there could be distances smaller than the Planck but we would need a theory of quantum gravity to make any sense of them of which we don’t currently have.
And that’s it, we have reached the bottom of the rabbit hole, covering 60 orders of magnitude from the size of the observable universe down to the point it descends into chaos and we need new theories to try and figure out what’s going on at down there, and yet everything in the universe we know of including spacetime is made from this stuff, and there lies the paradox.
Comments
“A little flea upon a flea
Upon his back to bite him.
And on this flea
Another flea.
And so on infinitum”
My dad often quoted this to me when pointing out the various stars when I was a small child back in 1957.
Your well researched article brought this memory back: how small and insignificant we humans are in the whole sheme of things! Many thanks and best wishes for 2021.
4/30/22: For 16 months or so, this article has been sitting in the universe of the WWW, and there is only 1 comment! How strange! This does not seem possible. There really should be dozens if not hundreds if not thousands of comments. They must be among the 80%.
Here’s mine:
I loved it! It made me shiver. Repeatedly. I found myself shivering repeatedly as I consumed it, very slowly. I felt fear, joy and awe. And I felt so very small. Like a May fly, with the mass and life span of a May fly. Like nothing at all. And yet, how is it possible that I, a nothing, can appreciate, at the primitive level of my comprehension of such things, these ideas? And how is it possible that people with their tiny little heads, could learn these things and ponder them?
And this is just the 20% of the Universe that we can sense.