How did the Universe begin?
How did planets and stars form?
Where did matter come from?
For anyone with at least a morsel of curiosity concerning the ins-and-outs of how our universe came into being, I've written a concise guide to the Big Bang- our most current theory on how it all began.
This is an introduction, and no doubt you will have many queries. Post any questions and I'll do my best to answer them, providing they aren't ridiculously taxing.
Before we start, I'll have to run over a few things first.
A word on notation
Astrophysical phenomena occur over a broad spectrum of time duration, and the unfolding of our universe is comprised of processes which push these boundaries to extremes. Before we go into specifics, it is useful to have a grasp of an element of scientific notation where indices and powers are used to represent very large or very small numbers- sometimes known as ‘Standard form’. The essence of this is that a long, unwieldy figure may be condensed to a size that is quick to scribe and comprehend.
For example, the number 100 may be written as 10^2, meaning 10 x 10. The number 1000 can have the form 10^3 i.e. 10 x 10 x 10.
Miniscule quantities may also be represented. 0.01 is 10^(-2), translating to 1/10^2, or 1/(10 x 10). An easier way to visualise this is to think of the number in the bracket as being the number of zeros before the one, remembering that a decimal place is needed after the first zero.
With that aside, let us consider some different time scales, and see how they compare to events that occur on both cosmic and microscopic orders.
Time
Time taken…
To blink: 0.4 secs
For a packet of data to be sent to a remote server, and receive acknowledgment (A ping) with a typical UK Broadband connection: 6 x 10^(-2) secs
For a typical 3.5” hard drive (7,200rpm) to randomly access data: 9 x 10^(-3) secs
For a stick of PC-6400 DDR-2 RAM to access or store data: 1.25 x 10^(-9) secs
For a Pi-zero particle to decay: 8.4 x 10^(-17) secs
Time elapsed…
Since recorded history: 10,000 years
Since modern man appeared on Earth: 200,000 years
Since mammals evoled: Early Jurassic period, around 165 million years
Since life emerged from water and spread to land: 530 million years
Since multi-celled organisms evoled: 1.2 billion years
Since the first organic life forms formed, in the ‘Primordial soup’: Between 2.5 and 4 billion years ago
Since earth was formed: 4.6 billion years
Since the Big Bang: 13.7 billion years
One may deduce that processes in physics are found to happen over all time scales, from the miniscule to the most prolonged. In order to appreciate the mechanics of an evolving universe, it is important to jettison your current perception of things happening quickly. Many of the important building blocks were established in the first second of the universes being. Both energy and temperature levels during the early periods of the universe very extremely high, and will also be represented in this ‘Standard form’ notation.
Forces
There are four fundamental forces, each of which is carried by its own ‘mediator’ particle. First up is one that we’re all familiar and comfortable with, mavity. It wouldn’t work without Gravitons, although they’re very difficult to detect- no-one has managed it so far. Next is the Electromagnetic force, another force whose effects chance it is, we experience daily. Without it there we be no motors, electricity or even light.
Finally the two more esoteric contributors come into play- the Weak Nuclear and Strong Nuclear forces. Strong nuclear forces bind the nuclei of atoms together, and the weak nuclear force is responsible for certain types of radioactive decay. The weak force really is just that, it is 10^13 times weaker than the strong nuclear force.
What is matter?
There are a bewildering number of particles and even categories of particles, and 99% of them you will never come across in the whole of your existence. Lets concentrate on the ones you may be familiar with, and we will learn more about their constituents and brethren. Protons and neutrons make up the core, or nucleus, of atoms. Protons are positively charged, neutrons as their name implies, are electrically neutral. Electrons are negatively charged particles which may be found orbiting the central nucleus of an atom. Protons and Neutrons are both much, much heavier than electrons (Nearly 2000 times as much). Together these different entities form electrically neutral atoms.
Protons, neutrons and electrons make up all atoms, so why do we need to go any further? Well, the story doesn’t stop their. Protons and neutrons belong to a class of particle called Baryons, which means that they too have constituent parts. The constituents of Baryons are called Quarks, and there are three in every baryon.
A Proton
Electrons are different beasts entirely, and are in fact members of another group named Leptons. Leptons are easier to deal with as they are not made up of anything smaller- they are fundamental particles.
Remember how we discussed particles which mediate forces? They too belong to a class of their own- Bosons. Bosons have unique properties which distinguish them from all other matter.
The beginning of time
We can trace the initial happening of an early universe with much confidence to when it had an age of just 10^(-43) seconds. This immeasurably short time period was first introduced by the German Physicist Max Planck, one of the founders of Quantum theory, and is suitably named Planck time. It is thought that this is the smallest meaningful (i.e. understandable with our current laws of physics) timeframe. What occurred before this period had elapsed, at t=0 or ‘before’ the Big Bang (whatever that means) we cannot yet tell. A thrillingly outlandish sounding ‘Theory of Everything’, or TOE would be required, whereby we can explain how the four fundamental forces are unified to act as one, singular force at extremely high temperatures and energies.
What we think we know is that the temperature of the universe at t= 10^(-43) seconds was around 10^32 degrees C. At this period, each sub-atomic particle possessed an energy on the order of 10^10 Joules, an enormous amount. By comparison, the energy in a lightning bolt is about 10^(9) Joules. At energies at this level and above, the four forces are unified. After this period, energies fell below this threshold and mavity split from the unified force, manifesting itself as a separate interaction. In the timeframe t = 10^(-43) seconds to t = 10^(-35) seconds, the strong nuclear, electromagnetic and weak nuclear forces were still united, and the universe consisted of a ‘soup’ of quarks and leptons that would transform into one another at will, making the classes of particle indistinguishable. Equally preposterously sounding as the TOE, a ‘Grand Unified Theory’, or GUT, is needed to fully allow us to explain how the unified strong, weak and electromagnetic force behaves. The size of the proto-universe at this point was a mere 10^(-27) metres (compare with the diameter of a proton, 10^(-15) metres).
By t = 10^(-35) s, the temperature had decreased to 10^27 degrees C, and the average particle energy to 10^4 Joules. At this point, energies were low enough for the strong nuclear force to separate as mavity did earlier. This acted as a catalyst for extreme amounts of expansion, whereby the universe inflated in size by a factor of at least 10^20. At t = 10^(-32) s, the universe was a mix of quarks, gluons and mediating bosons. The universe continued to cool and expand from the inflationary period to t = 10^(-10) seconds, where the weak nuclear and electromagnetic forces broke away and became distinct. At t= 10^(-6) seconds, when the temperature was about 10^13 degrees C and typical energies were 10^(-10) Joules, quarks began to bind together to form nucleons like protons and neutrons, as well as antinucleons and particles acquired mass via the Higgs Boson.
The four forces
After 10^(-2) s there was a slight excess of nucleons over antinucleons. When matter meets antimatter, annihilation of both particles occurs and a burst of energy is released. All antinucleons were destroyed, leaving a small amount (around 1%) of the initial protons and neutrons, which we see today as primary constituents of matter. By now the universe was around 10^(-10) m in size, comparable to the width of an atom.
Nucleosynthesis- Making the elements
When the first second had elapsed, protons outnumbered neutrons by a ratio of about 4.5 to 1. However, neutrons that aren’t bound to a nucleus have a lifetime of 15 minutes, after which they decay spontaneously into protons. The proton-neutron ratio increased until about t = 225 s, where the temperature cooled to 10^9 degrees C, and the average energy of a particle was below 3.2 x 10^(-13) Joules. This figure is important as the binding energy (amount of energy needed to hold a nucleus together) of a deuteron (a proton and neutron bound together) is 3.55 x 10^(-13) Joules. As the average energy decreased, a proton and a neutron could combine to form a deuteron, meaning that the bound neutron would not decay.
At this time there were about 7 protons for each neutron. The deuteron is a critical building block for manufacturing heavier elements. It can absorb a neutron and form tritium, or it can absorb a proton and make helium-3. Tritium can then absorb a proton, and Helium-3 can absorb a neutron, each yielding Helium-4, the particle in alpha radiation. All the hydrogen and helium were formed at this time, but after this the building of nuclei ground to a halt. The reason is that heavier nuclides have a lifetime long enough to allow them to persist, they are simply too unstable. Note that at this time energies were still far too high to allow electrons to bind to nuclei, so there were no atoms around at this point.
It would be another 380,000 years before further nucleosynthesis occurred, when the temperature had dropped to a more comprehendible 3000 degrees C. Hydrogen and helium atoms began to form and the density of the universe fell. mavity started to work its magic and pull all of the neutral atoms together to form gaseous clouds and eventually stars. Thermonuclear fusion (the fusing of two light nuclei into one larger nucleus plus the release of energy, the same process utilised in many nuclear weapons) in stars is believed to have produced all heavier nuclei in the universe.
Helium fusion is a key process. Two Helium-4 nuclei fuse to form a Beryllium-8 nucleus. Some Beryllium nuclei fuse with a Helium-4 to produce Carbon-12, the chemical basis of all known life on Earth. Successive fusions of Carbon-12with Helium-4 yield Oxygen-16, Neon-20 and Magnesium-24. Carbon and oxygen can fuse to form heavier and heavier elements. Once Iron-56 has been made, all fusion reactions that attempt to manufacture heavier nuclides are endoergic, i.e. they require a net input of energy to occur. If a star becomes heavy enough it may eventually explode as a Supernova, blasting out into space the heavy elements that it produced. This debris can, and does, reform to make new stars and planets.
Our own solar system, our sun, our planet and everything on it were once generated by a massive star which erupted as a supernova.
So we are all, in fact, made of stars.
How did planets and stars form?
Where did matter come from?
For anyone with at least a morsel of curiosity concerning the ins-and-outs of how our universe came into being, I've written a concise guide to the Big Bang- our most current theory on how it all began.
This is an introduction, and no doubt you will have many queries. Post any questions and I'll do my best to answer them, providing they aren't ridiculously taxing.
Before we start, I'll have to run over a few things first.
A word on notation
Astrophysical phenomena occur over a broad spectrum of time duration, and the unfolding of our universe is comprised of processes which push these boundaries to extremes. Before we go into specifics, it is useful to have a grasp of an element of scientific notation where indices and powers are used to represent very large or very small numbers- sometimes known as ‘Standard form’. The essence of this is that a long, unwieldy figure may be condensed to a size that is quick to scribe and comprehend.
For example, the number 100 may be written as 10^2, meaning 10 x 10. The number 1000 can have the form 10^3 i.e. 10 x 10 x 10.
Miniscule quantities may also be represented. 0.01 is 10^(-2), translating to 1/10^2, or 1/(10 x 10). An easier way to visualise this is to think of the number in the bracket as being the number of zeros before the one, remembering that a decimal place is needed after the first zero.
With that aside, let us consider some different time scales, and see how they compare to events that occur on both cosmic and microscopic orders.
Time
Time taken…
To blink: 0.4 secs
For a packet of data to be sent to a remote server, and receive acknowledgment (A ping) with a typical UK Broadband connection: 6 x 10^(-2) secs
For a typical 3.5” hard drive (7,200rpm) to randomly access data: 9 x 10^(-3) secs
For a stick of PC-6400 DDR-2 RAM to access or store data: 1.25 x 10^(-9) secs
For a Pi-zero particle to decay: 8.4 x 10^(-17) secs
Time elapsed…
Since recorded history: 10,000 years
Since modern man appeared on Earth: 200,000 years
Since mammals evoled: Early Jurassic period, around 165 million years
Since life emerged from water and spread to land: 530 million years
Since multi-celled organisms evoled: 1.2 billion years
Since the first organic life forms formed, in the ‘Primordial soup’: Between 2.5 and 4 billion years ago
Since earth was formed: 4.6 billion years
Since the Big Bang: 13.7 billion years
One may deduce that processes in physics are found to happen over all time scales, from the miniscule to the most prolonged. In order to appreciate the mechanics of an evolving universe, it is important to jettison your current perception of things happening quickly. Many of the important building blocks were established in the first second of the universes being. Both energy and temperature levels during the early periods of the universe very extremely high, and will also be represented in this ‘Standard form’ notation.
Forces
There are four fundamental forces, each of which is carried by its own ‘mediator’ particle. First up is one that we’re all familiar and comfortable with, mavity. It wouldn’t work without Gravitons, although they’re very difficult to detect- no-one has managed it so far. Next is the Electromagnetic force, another force whose effects chance it is, we experience daily. Without it there we be no motors, electricity or even light.
Finally the two more esoteric contributors come into play- the Weak Nuclear and Strong Nuclear forces. Strong nuclear forces bind the nuclei of atoms together, and the weak nuclear force is responsible for certain types of radioactive decay. The weak force really is just that, it is 10^13 times weaker than the strong nuclear force.
What is matter?
There are a bewildering number of particles and even categories of particles, and 99% of them you will never come across in the whole of your existence. Lets concentrate on the ones you may be familiar with, and we will learn more about their constituents and brethren. Protons and neutrons make up the core, or nucleus, of atoms. Protons are positively charged, neutrons as their name implies, are electrically neutral. Electrons are negatively charged particles which may be found orbiting the central nucleus of an atom. Protons and Neutrons are both much, much heavier than electrons (Nearly 2000 times as much). Together these different entities form electrically neutral atoms.
Protons, neutrons and electrons make up all atoms, so why do we need to go any further? Well, the story doesn’t stop their. Protons and neutrons belong to a class of particle called Baryons, which means that they too have constituent parts. The constituents of Baryons are called Quarks, and there are three in every baryon.
A Proton
Electrons are different beasts entirely, and are in fact members of another group named Leptons. Leptons are easier to deal with as they are not made up of anything smaller- they are fundamental particles.
Remember how we discussed particles which mediate forces? They too belong to a class of their own- Bosons. Bosons have unique properties which distinguish them from all other matter.
The beginning of time
We can trace the initial happening of an early universe with much confidence to when it had an age of just 10^(-43) seconds. This immeasurably short time period was first introduced by the German Physicist Max Planck, one of the founders of Quantum theory, and is suitably named Planck time. It is thought that this is the smallest meaningful (i.e. understandable with our current laws of physics) timeframe. What occurred before this period had elapsed, at t=0 or ‘before’ the Big Bang (whatever that means) we cannot yet tell. A thrillingly outlandish sounding ‘Theory of Everything’, or TOE would be required, whereby we can explain how the four fundamental forces are unified to act as one, singular force at extremely high temperatures and energies.
What we think we know is that the temperature of the universe at t= 10^(-43) seconds was around 10^32 degrees C. At this period, each sub-atomic particle possessed an energy on the order of 10^10 Joules, an enormous amount. By comparison, the energy in a lightning bolt is about 10^(9) Joules. At energies at this level and above, the four forces are unified. After this period, energies fell below this threshold and mavity split from the unified force, manifesting itself as a separate interaction. In the timeframe t = 10^(-43) seconds to t = 10^(-35) seconds, the strong nuclear, electromagnetic and weak nuclear forces were still united, and the universe consisted of a ‘soup’ of quarks and leptons that would transform into one another at will, making the classes of particle indistinguishable. Equally preposterously sounding as the TOE, a ‘Grand Unified Theory’, or GUT, is needed to fully allow us to explain how the unified strong, weak and electromagnetic force behaves. The size of the proto-universe at this point was a mere 10^(-27) metres (compare with the diameter of a proton, 10^(-15) metres).
By t = 10^(-35) s, the temperature had decreased to 10^27 degrees C, and the average particle energy to 10^4 Joules. At this point, energies were low enough for the strong nuclear force to separate as mavity did earlier. This acted as a catalyst for extreme amounts of expansion, whereby the universe inflated in size by a factor of at least 10^20. At t = 10^(-32) s, the universe was a mix of quarks, gluons and mediating bosons. The universe continued to cool and expand from the inflationary period to t = 10^(-10) seconds, where the weak nuclear and electromagnetic forces broke away and became distinct. At t= 10^(-6) seconds, when the temperature was about 10^13 degrees C and typical energies were 10^(-10) Joules, quarks began to bind together to form nucleons like protons and neutrons, as well as antinucleons and particles acquired mass via the Higgs Boson.
The four forces
After 10^(-2) s there was a slight excess of nucleons over antinucleons. When matter meets antimatter, annihilation of both particles occurs and a burst of energy is released. All antinucleons were destroyed, leaving a small amount (around 1%) of the initial protons and neutrons, which we see today as primary constituents of matter. By now the universe was around 10^(-10) m in size, comparable to the width of an atom.
Nucleosynthesis- Making the elements
When the first second had elapsed, protons outnumbered neutrons by a ratio of about 4.5 to 1. However, neutrons that aren’t bound to a nucleus have a lifetime of 15 minutes, after which they decay spontaneously into protons. The proton-neutron ratio increased until about t = 225 s, where the temperature cooled to 10^9 degrees C, and the average energy of a particle was below 3.2 x 10^(-13) Joules. This figure is important as the binding energy (amount of energy needed to hold a nucleus together) of a deuteron (a proton and neutron bound together) is 3.55 x 10^(-13) Joules. As the average energy decreased, a proton and a neutron could combine to form a deuteron, meaning that the bound neutron would not decay.
At this time there were about 7 protons for each neutron. The deuteron is a critical building block for manufacturing heavier elements. It can absorb a neutron and form tritium, or it can absorb a proton and make helium-3. Tritium can then absorb a proton, and Helium-3 can absorb a neutron, each yielding Helium-4, the particle in alpha radiation. All the hydrogen and helium were formed at this time, but after this the building of nuclei ground to a halt. The reason is that heavier nuclides have a lifetime long enough to allow them to persist, they are simply too unstable. Note that at this time energies were still far too high to allow electrons to bind to nuclei, so there were no atoms around at this point.
It would be another 380,000 years before further nucleosynthesis occurred, when the temperature had dropped to a more comprehendible 3000 degrees C. Hydrogen and helium atoms began to form and the density of the universe fell. mavity started to work its magic and pull all of the neutral atoms together to form gaseous clouds and eventually stars. Thermonuclear fusion (the fusing of two light nuclei into one larger nucleus plus the release of energy, the same process utilised in many nuclear weapons) in stars is believed to have produced all heavier nuclei in the universe.
Helium fusion is a key process. Two Helium-4 nuclei fuse to form a Beryllium-8 nucleus. Some Beryllium nuclei fuse with a Helium-4 to produce Carbon-12, the chemical basis of all known life on Earth. Successive fusions of Carbon-12with Helium-4 yield Oxygen-16, Neon-20 and Magnesium-24. Carbon and oxygen can fuse to form heavier and heavier elements. Once Iron-56 has been made, all fusion reactions that attempt to manufacture heavier nuclides are endoergic, i.e. they require a net input of energy to occur. If a star becomes heavy enough it may eventually explode as a Supernova, blasting out into space the heavy elements that it produced. This debris can, and does, reform to make new stars and planets.
Our own solar system, our sun, our planet and everything on it were once generated by a massive star which erupted as a supernova.
So we are all, in fact, made of stars.
