The end of the universe

We know the universe had a beginning and physicists agree that one day it will end, but cosmologist Katie Mack is obsessed with how it will finish. Will our universe collapse in upon itself, rip itself apart, or even – in the next five minutes – succumb to an inescapable expanding bubble of doom?

Drawing on cutting-edge theory and brand-new results from the most powerful telescopes and particle colliders, Mack explored five possible finales for the universe and what they would look like (if anyone were still around to see them): The Big Crunch, Heat Death, Vacuum Decay, the Big Rip and the Bounce.

Following Katie Mack’s inspiring and mind-blowing lecture, there was a question and answer session.

About the speaker:


Katherine (Katie) J. Mack is a theoretical cosmologist, Assistant Professor at North Carolina State University and one of the most popular scientists on Twitter (@AstroKatie). She is known for her witty comments and for making science accessible and has more than 350,000 Twitter followers including JK Rowling and Hozier (who quotes Mack in one of his song lyrics). Her research investigates dark matter, vacuum decay and the epoch of reionisation. Mack is a popular science communicator, participating in social media and regularly writing for Scientific American, Slate, Sky & Telescope, Time and Cosmos.

Throughout her career as a researcher at Caltech, Princeton, Cambridge, Melbourne and now North Carolina State University, Mack has studied dark matter, black holes, cosmic strings and the formation of the first galaxies. Her new book The End of Everything (Astrophysically Speaking) is a mind-bending exploration of the destruction of the universe.

The event was hosted by Valerie Jamieson, New Scientist Events’ creative director.


The following are notes from the on-line lecture. Even though I could stop the video and go back over things there are likely to be mistakes because I haven’t heard things correctly or not understood them. I hope Professor Mack and my readers will forgive any mistakes and let me know what I got wrong.



We usually give all the attention to how the Universe began but tend to ignore how it ends as this is less clear.

The talk

The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P. Sloan Foundation, which contributed significant funding.

It has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-colour images of one third of the sky, and spectra for more than three million astronomical objects.

An animated flythrough which shows what our view of the Universe has become thanks to the data of the Sloan Digital Sky Survey.


The splodges in the above image are real galaxies that have been mapped in the Universe.

Each galaxy has stars like ours.

Our vantage point is our home, the Earth (Carl Sagan’s pale blue dot), a blue marble. Our little habitat where we can watch the Universe


Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator.

Voyager 1 was commanded by NASA to turn its camera around and take one last photograph of Earth across a great expanse of space, at the request of astronomer and author Carl Sagan. The phrase “Pale Blue Dot” was coined by Sagan himself in his reflections on the photograph’s significance, documented in his 1994 book of the same name


The blue marble

Of course, nothing lasts for ever. Our Sun will die, taking the Earth with it (eventually the Earth will tumble into what is left of the Sun).,as%20its%20envelope%20%E2%80%94%20into%20space.

In about 5 billion years, the sun will run out of hydrogen. Our star is currently in the most stable phase of its life cycle and has been since the birth of our solar system, about 4.5 billion years ago. Once all the hydrogen gets used up, the sun will grow out of this stable phase. With no hydrogen left to fuse in the core, a shell of fusion hydrogen will form around the helium-filled core.

Gravitational forces will take over, compressing the core and allowing the rest of the sun to expand. Our star will grow to be larger than we can imagine — so large that it’ll envelope the inner planets, including Earth. That’s when the sun will become a red giant.

For about a billion years, the sun will burn as a red giant. Then, the hydrogen in that outer core will deplete, leaving an abundance of helium. That element will then fuse into heavier elements, like oxygen and carbon, in reactions that don’t emit as much energy. Once all the helium disappears, the forces of gravity will take over, and the sun will shrink into a white dwarf. All the outer material will dissipate, leaving behind a planetary nebula.


Hopefully, long before any of this happens, the human race will have moved out of our Solar System and moved out into the cosmos.


Perhaps the human race will have found a suitable planet orbiting another sun, which might be in one of the galaxies that the Sloan digital sky survey showed us.

However even this solar system will die and the Universe as a whole will come to an end.

But how will the end of the Universe come – how will the Universe evolve to this point?

How can we gather information from the Universe to predict this end?

We need to use physics, particle physics, astrophysics and cosmology. These have all been used to build up our cosmic story.

There are 5 different possibilities:

1) Big crunch

2) Heath death

3) Big rip

4) Vacuum decay

5) Bounce

All these scenarios have one thing in common – they all have an end.

The Universe can’t last forever, it is changing and evolving.

We know the Universe began about 13.8 billion years ago.

Something will happen in the future that will fundamentally rearrange the cosmos and make it unrecognisable to us now.

But each of these possibilities is very different.

What can we learn from the cosmos by considering each of the possibilities?,distinguished%20by%20the%20naked%20eye.

We live in the Milky Way, which is a spiral galaxy.


Because of where we are situated within the galaxy, we seed it as a stripe of stars across the sky. Our ancestors called it the Milky Way because it looked like a stream of spilt milk.


What our galaxy looks like from outside is similar to our nearest galaxy,  Andromeda


The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years away in the constellation Andromeda. The image also shows Messier Objects 32 (centre left above the galactic nucleus) and 110 (centre left below the galaxy), as well as NGC 206 (a bright star cloud in the Andromeda Galaxy) and the star Nu Andromedae. This image was taken using a hydrogen-alpha filter. Adam Evans – M31, the Andromeda Galaxy (now with h-alpha) Uploaded by NotFromUtrecht

The Andromeda Galaxy, also known as Messier 31, M31, or NGC 224 and originally the Andromeda Nebula is a barred spiral galaxy approximately 2.5 million light-years (770 kiloparsecs) from Earth and the nearest major galaxy to the Milky Way. The galaxy’s name stems from the area of Earth’s sky in which it appears, the constellation of Andromeda, which itself is named after the Ethiopian (or Phoenician) princess who was the wife of Perseus in Greek mythology.

With powerful telescopes we can see hundreds and thousands of galaxies.


This view of nearly 10,000 galaxies (each of the bright specks are galaxies) is called the Hubble Ultra Deep Field. The snapshot includes galaxies of various ages, sizes, shapes, and colours. The smallest, reddest galaxies, about 100, may be among the most distant known, existing when the universe was just 800 million years old. The nearest galaxies – the larger, brighter, well-defined spirals and ellipticals – thrived about 1 billion years ago, when the cosmos was 13 billion years old.

The image required 800 exposures taken over the course of 400 Hubble orbits around Earth. The total amount of exposure time was 11.3 days, taken between Sept. 24, 2003 and Jan. 16, 2004.

Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team

The Hubble Ultra-Deep Field (HUDF) is an image of a small region of space in the constellation Fornax, containing an estimated 10,000 galaxies. The original release was combined from Hubble Space Telescope data accumulated over a period from September 24, 2003, through to January 16, 2004. Looking back approximately 13 billion years (between 400 and 800 million years after the Big Bang) it has been used to search for galaxies that existed at that time. The HUDF image was taken in a section of the sky with a low density of bright stars in the near-field, allowing much better viewing of dimmer, more distant objects. In August and September 2009, the HUDF field was observed at longer wavelengths (1.0 to 1.6 µm) using the infrared channel of the recently attached Wide Field Camera 3 (WFC3) instrument. When combined with existing HUDF data, astronomers were able to identify a new list of potentially very distant galaxies.


Seen in orbit from the departing Space Shuttle Atlantis in 2009, flying Servicing Mission 4 (STS-125), the fifth and final Hubble mission

The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versatile, well known both as a vital research tool and as a public relations boon for astronomy. The Hubble telescope is named after astronomer Edwin Hubble and is one of NASA’s Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

Light has been travelling from some of these galaxies for billions of years. This means that light from their stars has taken billions of years to get to us. Looking at them is looking into the cosmic past. We are looking at a younger Universe than today.


Looking beyond our galaxy we can see galaxies are moving away from us and from each other as the Universe is expanding.

As the Universe evolves into something new the space between galaxies is getting larger.

Looking in the far, young Universe, we can’t see an edge. Galaxies look much the same everywhere.

There is one edge, however, a limit to our knowledge.

If we could look back further, we would see a time when there weren’t any galaxies.


Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)

Hubble Deep field is looking at galaxies that were around at about 0.5 billion years after the Big Bang,

What do we see at the beginning?


If we look far enough away in any direction, we see the cosmos as it was right at the beginning. In the first moments when the Universe was experiencing a “primordial fire”.

The Earth is in the centre of shells of time. Each shell is a period in the distant past.

13.8 billion years ago the Universe was hot, dense and full of plasma.

We know that the Universe is expanding so there must have been a time in the past when everything as close together.

Looking far back into the cosmos we can see the “primordial fire”.

We can map our observations to show hot young areas of the Universe and use this information to build simulations of how these little hot dense areas became galaxies and how low dense areas become voids. We can study the make up of the Universe by studying fluctuations.

Illustris Simulation: Most detailed simulation of our Universe

The Illustris simulation is the most ambitious computer simulation of our Universe yet performed. The calculation tracks the expansion of the universe, the gravitational pull of matter onto itself, the motion of cosmic gas, as well as the formation of stars and black holes. These physical components and processes are all modelled starting from initial conditions resembling the very young universe 300,000 years after the Big Bang and until the present day, spanning over 13.8 of galaxies captured in high-detail, covering a wide range of masses, rates of star formation, shapes, sizes, and with properties that agree well with the galaxy population observed in the real universe. The simulations were run on supercomputers in France, Germany, and the US. The largest was run on 8,192 compute cores, and took 19 million CPU hours. A single state-of-the-art desktop computer would require more than 2000 years to perform this calculation. Find out more at: Publication: “Properties of galaxies reproduced by a hydrodynamic simulation”, Vogelsberger, Genel, Springel, Torrey, Sijacki, Xu, Snyder, Bird, Nelson, Hernquist, Nature 509, 177-182 (08 May 2014) doi:10.1038/nature13316

Formation and evolution of a massive galaxy in the TNG50 simulation. The resulting TNG50 galaxy is similar in mass and shape to the Andromeda galaxy (M31). After a turbulent beginning, the galaxy experiences no major disturbances and can settle down into an equilibrium state. Credit: D. Nelson, TNG team.

Gaia’s View of the Milky Way

Gaia, operated by the European Space Agency (ESA), surveys the sky from Earth orbit to create the largest, most precise, three-dimensional map of our Galaxy. One year ago, the Gaia mission produced its much-awaited second data release, which included high-precision measurements — positions, distance and proper motions — of more than one billion stars in our Milky Way galaxy. This catalogue has enabled transformational studies in many fields of astronomy, addressing the structure, origin and evolution the Milky Way and generating more than 1700 scientific publications since its launch in 2013.


This image shows Gaia’s all-sky view of the Milky Way based on measurements of almost 1.7 billion stars.

Credit: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO


Artist’s impression of the Gaia spacecraft

Gaia is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until c. 2022. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision. The mission aims to construct by far the largest and most precise 3D space catalogue ever made, totalling approximately 1 billion astronomical objects, mainly stars, but also planets, comets, asteroids and quasars among others.


A 2013 map of the background radiation left over from the Big Bang, taken by the ESA’s Planck spacecraft, captured the oldest light in the universe. This information helps astronomers determine the age of the universe. (Image: © ESA and the Planck Collaboration.)

We have a good idea of how the Universe began and some idea how it evolved.

NGC 4676: The Mighty Mice


These two mighty galaxies are pulling each other apart. Known as The Mice because they have such long tails, each large spiral galaxy has actually passed through the other. Their long tails are drawn out by strong gravitational tides rather than collisions of their individual stars. Because the distances are so large, the cosmic interaction takes place in slow motion — over hundreds of millions of years. They will probably collide again and again over the next billion years until they coalesce to form a single galaxy. NGC 4676 lies about 300 million light-years away toward the constellation of Bernice’s Hair (Coma Berenices) and are likely members of the Coma Cluster of Galaxies. Not often imaged in small telescopes, this wide field of view catches the faint tidal tails several hundred thousand light-years long.


Understanding how galaxy mergers shape the observable Universe.

Galaxy mergers are thought to drive star formation, the growth of black holes and alter the structural mix of galaxies over cosmic time.

1) The Big Crunch,universe%20starting%20with%20another%20Big

This idea about the end of the Universe has been around a long time.

The idea is that eventually the Universe will stop expanding and the process will go into reverse. That the stuff that makes up the Universe will come back together. This could happen if there was so much gravity around – pulling stuff back against expansion.

We would see the Universe increasingly full of galaxies – coming towards each other and colliding with each other.

As noted above we do see galaxies colliding – cosmic collisions – A common sight in the Cosmos.

If there was going to be a Big Crunch we would see these collisions all over the sky.

Constant collisions would result in new star formation. Black holes colliding would see jets of radiation supernovae going off,

It wouldn’t be the galaxy collisions that would destroy the Universe. These collisions don’t destroy planets or solar systems. There is only a very small chance that individual stars will collide. More likely that the stars will get moved around a bit giving out gases that would produce new stars.

What would cause the Universe destruction is that as space decreases the radiation being emitted (Cosmic background radiation, which is faint at the moment) will get compressed, getting brighter and hotter. Also, all the starlight dispersing through the cosmos will be brought together and compressed into high energies and be very dangerous.

The cosmic microwave background (CMB, CMBR), in Big Bang cosmology, is electromagnetic radiation as a remnant from an early stage of the universe, also known as “relic radiation”. The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe.

The radiation would become so intense that it would be able to ignite the surface of stars – causing thermonuclear explosions across their surfaces.

Once this happens and the stars are burning from the outside in then this really is the end of the Universe.

The Big Crunch is unlikely based on our understanding of how the Universe is evolving.


2) Heat death,sustain%20processes%20that%20increase%20entropy.

The heat death of the universe, also known as the Big Chill or Big Freeze, is a conjecture on the ultimate fate of the universe, which suggests the universe would evolve to a state of no thermodynamic free energy and would therefore be unable to sustain processes that increase entropy.

The Universe is expanding and the rate of expansion increases. Galaxies are getting further apart at a faster and faster rate.

We don’t really know why this is happening. We say it is down to the presence of dark energy but we don’t really know what it is. It just accelerates the expansion of the Universe.

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from supernovae measurements, which showed that the universe does not expand at a constant rate; rather, the expansion of the universe is accelerating. Understanding the evolution of the universe requires knowledge of its starting conditions and its composition. Prior to these observations, the only forms of matter-energy known to exist were ordinary matter, dark matter, and radiation. Measurements of the cosmic microwave background suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large-scale motion. Without introducing a new form of energy, there was no way to explain how an accelerating universe could be measured. Since the 1990s, dark energy has been the most accepted premise to account for the accelerated expansion. As of 2020, there are active areas of cosmology research aimed at understanding the fundamental nature of dark energy.


Galaxies will become more and more isolated and each one will be invisible to each other because they are so far away from each other. This is  believed to happen 100 billion years in the future.


We will have collided with local galaxies before this. Our galaxy is on course to collide with Andromeda. However, we won’t be able to see galaxies beyond our little group of collided galaxies.

We won’t have evidence for the Big Bang anymore because we won’t be able to see any of the distant light.

As the Universe expands and everything becomes isolated the stars in our galaxy begin to burn out, matter decays and black holes evaporate. The Universe ends as cold, isolated lifeless space.

It is so far in the future that it is hard to come up with terms for that distance and time

3) The Big Rip,universe%20at%20a%20certain%20time

In physical cosmology, the Big Rip is a hypothetical cosmological model concerning the ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, and even spacetime itself, is progressively torn apart by the expansion of the universe at a certain time in the future.

This is connected with dark energy.

Heath death dark energy is considered a cosmological constant.,of%20dark%20energy%20and%20quintessence.

In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) is the energy density of space, or vacuum energy, that arises in Albert Einstein’s field equations of general relativity. It is closely associated to the concepts of dark energy and quintessence.

The cosmological constant is based on an idea that Einstein came up with. He used stars in his explanation because the notion of galaxies wasn’t yet known.


Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the theory of relativity, one of the two pillars of modern physics (alongside quantum mechanics).

All galaxies are attracted to each other because of gravity.

Now Einstein didn’t know about the Big Bang or the expansion of the Universe. He asked himself why these stars (galaxies) were not falling towards each other because of gravitational attraction (the Universe should have collapsed long ago).


To explain this, he added the cosmological constant to his equations of gravity. This “constant” is pushing out space (galaxies). Stretching out space, holding things apart. Everything is balanced.

When it was shown that the Universe was expanding Einstein got rid of this “constant”. However, because the Universe is expanding at an accelerated rate, we need to bring this constant back.

This cosmological constant will eventually take over everything. As the Universe expands the density will decrease.


The radiation density also decreases – even faster – because as space gets bigger the wavelength of the radiation increases meaning its energy decreases


But if dark energy is the cosmological constant, it is a property of space. So, when there is more space there is more cosmological constant. So, its density is uniform – it stays the same


There comes a time when there is so much more cosmological constant than matter that it takes over the expansion of the Universe and evolution of the cosmos. Everything else is being diluted. Over time only the cosmological constant will remain and you get the heat death Universe.


But if dark energy is not the cosmological constant there could be something more powerful. Something that doesn’t stay constant, but actually increases – phantom dark energy.


There are many reasons not to like this idea of phantom dark energy. It breaks physics rules. But some data collected means we can’t rule it out. If it did exist it would do more than cause galaxies to move apart. It would cause them to rip apart from the inside. Eventually all matter would be pulled apart.

NASA have made an animation of the Universe expanding and then being torn apart.

Destroying the cosmos.

Destroying space itself



An equation of state dictates whether we have phantom dark energy.

Equation of state parameter is W

W = ratio of density/pressure of whatever this stuff is

If the cosmological constant is W = -1 then we get a nice gentle heat death.

However, if W < -1 we have phantom dark energy leading to the big rip and the destruction of the cosmos.

We can do measurements with the Planck satellite and we can get a value of W just less than -1 (W = -1.028 +/- 0.032)


Planck was a space observatory operated by the European Space Agency (ESA) from 2009 to 2013, which mapped the anisotropies of the cosmic microwave background (CMB) at microwave and infra-red frequencies, with high sensitivity and small angular resolution.

The error margin in W means it could be a little less than -1 or a little greater than -1.

What is the lowest W with that measurement and what does it tell us about how long it would be until the big rip happens? The lower the number the sooner you will get a big rip.

We get


Based on 2019 data from the Planck satellite.

You can then work out a time frame for the Universe’s destruction.

Based on a famous paper

Phantom Energy and Cosmic Doomsday

Robert R. Caldwell, Marc Kamionkowski, Nevin N. Weinberg


4) Vacuum decay

This could happen at any moment but we shouldn’t worry.

A few years ago, the Higgs particle was discovered, a particle associated with the Higgs field. This field pervades all space and has something to do with how fundamental particles got mass in the early Universe. It us, supposedly, the final piece of the standard model of physics.

The Higgs boson is an elementary particle in the Standard Model of particle physics, produced by the quantum excitation of the Higgs field, one of the fields in particle physics theory. It is named after physicist Peter Higgs, who in 1964, along with five other scientists, proposed the Higgs mechanism to explain why particles have mass.


Peter Ware Higgs CH FRS FRSE FInstP (born 29 May 1929) is a British theoretical physicist, Emeritus Professor in the University of Edinburgh, and Nobel Prize laureate for his work on the mass of subatomic particles.


The Standard Model of particle physics is the theory describing three of the four known fundamental forces (the electromagnetic, weak, and strong interactions, and not including the gravitational force) in the universe, as well as classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists around the world, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, confirmation of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.

Although the Standard Model is believed to be theoretically self-consistent and has demonstrated huge successes in providing experimental predictions, it leaves some phenomena unexplained and falls short of being a complete theory of fundamental interactions. It does not fully explain baryon asymmetry, incorporate the full theory of gravitation as described by general relativity, or account for the accelerating expansion of the Universe as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses. It is basically what we know about particle physics at the moment.

The development of the Standard Model was driven by theoretical and experimental particle physicists alike. For theorists, the Standard Model is a paradigm of a quantum field theory, which exhibits a wide range of phenomena including spontaneous symmetry breaking, anomalies and non-perturbative behaviour. It is used as a basis for building more exotic models that incorporate hypothetical particles, extra dimensions, and elaborate symmetries (such as supersymmetry) in an attempt to explain experimental results at variance with the Standard Model, such as the existence of dark matter and neutrino oscillations.


The purple ones are the quarks (which are not actually purple)


A quark is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as colour confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas.

The up and down quarks make up most of normal matter along with the lepton electron.

A proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron.


The quark structure of the proton. There are two up quarks in it and one down quark. The strong force is mediated by gluons (wavey). The strong force has three types of charges, the so-called red, green and the blue. Note that the choice of green for the down quark is arbitrary; the “colour charge” is thought of as circulating among the three quarks.

The neutron is a subatomic particle, symbol n or n0, with no electric charge and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave similarly within the nucleus, and each has a mass of approximately one atomic mass unit, they are both referred to as nucleons. Their properties and interactions are described by nuclear physics.

The quark content of a proton. The colour assignment of individual quarks is arbitrary, but all three colours must be present. Forces between quarks are mediated by gluons.


The green ones are leptons (which are not actually green)


In particle physics, a lepton is an elementary particle of half-integer spin (spin ​1⁄2) that does not undergo strong interactions. Two main classes of leptons exist, charged leptons (also known as the electron-like leptons), and neutral leptons (better known as neutrinos). Charged leptons can combine with other particles to form various composite particles such as atoms and positronium, while neutrinos rarely interact with anything, and are consequently rarely observed. The best known of all leptons is the electron.

The orange ones are bosons (force carriers, and guess what, they aren’t actually orange)


In particle physics, a gauge boson is a force carrier, a bosonic particle that carries any of the fundamental interactions of nature, commonly called forces. Elementary particles, whose interactions are described by a gauge theory, interact with each other by the exchange of gauge bosons—usually as virtual particles.

Photons carry the electromagnetic interaction/force; W and Z bosons carry the weak interaction/force; and gluons carry the strong interaction/force.

The photon is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless and they always move at the speed of light in vacuum

In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms. The weak interaction participates in nuclear fission, and the theory describing it in terms of both its behaviour and effects is sometimes called quantum flavourdynamics (QFD). However, the term QFD is rarely used, because the weak force is better understood in terms of electroweak theory (EWT).

In nuclear physics and particle physics, the strong interaction is the mechanism responsible for the strong nuclear force, and is one of the four known fundamental interactions, with the others being electromagnetism, the weak interaction, and gravitation. At the range of 10−15 m (1 femtometer), the strong force is approximately 137 times as strong as electromagnetism, a million times as strong as the weak interaction, and 1038 times as strong as gravitation. The strong nuclear force holds most ordinary matter together because it confines quarks into hadron particles such as the proton and neutron. In addition, the strong force binds these neutrons and protons to create atomic nuclei. Most of the mass of a common proton or neutron is the result of the strong force field energy; the individual quarks provide only about 1% of the mass of a proton.

The Higgs particle is a different type of boson. It is the only fundamental scalar boson in the Standard Model of particle physics


The name scalar boson arises from quantum field theory

In UK schools for students up to the age of 16 an atom is typically drawn with a central nucleus made up of protons and neutrons with electrons whizzing around the outside in orbits.


In the quantum mechanical sense electrons actually form a cloud around the nucleus. Often called a probability cloud due to the probability of finding an electron there.


Modern physics tells us that the dynamic behaviour of atoms and molecules, including subatomic particles like electrons cannot be described by the laws of classical Newtonian physics. To describe the mechanics of these particles of an atom, a radical shift from established classical ideas was required, as things at the microscopic level behaved like nothing at the macroscopic level. The successor as you may know, was quantum physics. The theory of quantum mechanics was able to model the behaviour of atoms, molecules, and subatomic particles like electrons.

The core principle on which all of quantum physics is based is the uncertainty principle. You need to have some idea of it, to understand what the electron cloud theory is.

The uncertainty principle discovered by Heisenberg, states that you cannot know how fast a particle is moving and where it is located, simultaneously, with arbitrary levels of accuracy. There is a fundamental level of uncertainty that still remains in every simultaneous measurement of momentum and position, which is inherent in the system itself and does not have an origin in some measurement device defect.

The uncertainty can never be eliminated entirely while measuring the position and momentum of a particle simultaneously. This means that the trajectory of any particle like an electron can never be predicted exactly. All quantum physics can do is provide you with probabilities for the location of an electron revolving around an atom.


Werner Karl Heisenberg (5 December 1901 – 1 February 1976) was a German theoretical physicist and one of the key pioneers of quantum mechanics.

By understanding the standard model an by taking careful measurements of each of these particles, their masses ad how they interact we can learn about the structure of physics.

There is mathematical formula of how these particles fit together, how they interact and how these forces work together.

It gives us a set of laws of physics that set the parameters of the natural world.

Do they work together in a stable manner forever or is there someway they can be tweaked to give a different set of laws and therefore a different Universe.

The reason why we are interested and what this has to do with the Higgs field is that the value the Higgs field takes and the amount of energy in the Higgs field determines how physics fits together.

At the moment we have a value of the Higgs field, but this could have been different in the past and physics would have acted differently. There would have been different particles interacting in a different way.

The Higgs field we have now gives us the standard model we see today.

If the Higgs field changes in the future, we might get new particles and new forces in nature. Our atoms would not hold together anymore (one way for me to lose weight).

When the Higgs boson was discovered new measurements could be taken of how the standard model and particle physics works.

Specifically looking at the Higgs particle and the top quark we can make a chart of what sort of possibilities those masses give us, a seminal particle physics model which is truly stable with a Higgs field that can’t change again, versus one where it could change and somehow change the future.

The following is a chart of stability of the Universe for different masses of the Higgs and top quark particle.

The mass is measured in GeV. This unit comes about because of the famous relationship E = mc2 (energy in joules = mass in kg x (speed of light in a vacuum)2). When dealing with the mass of subatomic particles the mass in kg is going to be absolutely tiny as is its energy in joules.

First thing we need to do is rearrange the formula

m = E/c2 and we need an alternative unit for energy.

In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the amount of kinetic energy gained by a single electron (or proton) accelerating from rest through an electric potential difference of one volt in vacuum. When used as a unit of energy, the numerical value of 1 eV in joules (symbol J) is equivalent to the numerical value of the charge of an electron in coulombs (symbol C). Under the 2019 redefinition of the SI base units, this sets 1 eV equal to the exact value 1.602176634 x 1019 J. 1GeV will equal 1.602176634 x 10−12J (the mass of a proton is about 1GeV).

So, the mass of a Higgs particle or top quark would have a unit of GeV/c2. Now because the speed of light in a vacuum is a constant, we can leave it to one side and just use the GeV to represent the mass.

Higgs mass and vacuum stability in the Standard Model at NNLO


If the Higgs mass was 50GeV and the top quark mass was 50GeV we would be in the stable area and we know the Higgs field will not change.

If the Higgs mass was 100GeV and the top quark mass was 20GeV then the Universe wouldn’t be stable and we wouldn’t exist.

When measurements of the Higgs particle and top quark were taken the position on the chart can be seen below. Just inside the meta-stability range. This means the Universe is stable for now.


There is a value that the Higgs field would rather be at.

We can picture this as follows


The dips/valleys represent two different values of the Higgs field. The lower one is preferred by the Universe in some circumstances and the higher one is less preferred.

You can imagine that our Universe sits in this higher valley. Its fine for now but there is a deeper valley where it would be more stable. Where it is, is, ok as long as it doesn’t get disturbed.

In this case one of the two valleys represents a true vacuum and the other represents a false vacuum.



As mentioned earlier the lowest energy state is the most stable. So, what is the danger if you are in a false vacuum.

Well in principle something could happen to cause the Universe to move to the true vacuum


In truth the true vacuum is bad because different forces could act. Particles might not hold together anymore and that wouldn’t be good for us.

We can’t actually conceive the amount of energy required to kick the Universe into the true vacuum. You would have to disturb the Higgs field in a particular way which we don’t know how to do.

We know of known particle collision anywhere that could produce/reach that sort of energy. So, we are pretty sure that it can’t happen – that the Higgs field can’t be kicked over that hill.

If it had been possible, perhaps it would have happened earlier in the Universe

So probably this option for the end of the Universe is not an option but we live in a fundamentally quantum mechanical Universe. Sometimes you have a particle on one side suddenly materialise on the other side through quantum tunnelling.

Quantum tunnelling is the quantum mechanical phenomenon where a subatomic particle’s probability disappears from one side of a potential barrier and appears on the other side without any probability current (flow) appearing inside the barrier. Quantum tunnelling is not predicted by the laws of classical mechanics where surmounting a potential barrier requires enough potential energy.


Unfortunately, this could work in our hill and valley analogy and the Universe could tunnel through the hill.

This could mean that at some point in the Higgs field, somewhere in the Universe, it would tunnel from the false vacuum to the true vacuum.

If it happens it would be contagious. It would make a little bubble of space in the Universe containing a true vacuum with a different kind of particle physics, different laws of physics and with a different value of the Higgs field.

This bubble would expand at the speed of light.



The bubble wall would be this energetic shell around this true vacuum state and it would incinerate anything it touched.

Once the bubble passes over something that item would be inside the bubble with its different laws of physics and it would be totally destroyed.

One piece of good news is that is we were that item and the bubble was travelling towards us at the speed of light so we wouldn’t see it coming.


It would be a totally random event so you wouldn’t know when or where it was going to happen.

Around the 1980s some physicists calculated that not only would the bubble have non-survivable conditions but that the gravitational field inside it would be unstable. So once something is in the bubble it will collapse into a black hole and be completely destroyed.

Coleman & De Luccia wrote in 1980 about the complications and calculated that the true vacuum inside the bubble is unstable.

“This is disheartening. The possibility that we are living in a false vacuum has never been a cheering one to contemplate. Vacuum decay is the ultimate ecological catastrophe; in a new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know. However, one could also draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy. This possibility has now been eliminated.”

One of the reasons we shouldn’t worry about vacuum decay is because there is absolutely nothing, we can do about it. Another reason is that the process would be totally painless because nerve impulses don’t travel at the speed of light. We would be dead before we were aware of any pain.

The timescales that this could happen are very long. You can’t predict when quantum tunnelling could occur but you can predict a timescale over which it is more or less likely. A timescale of 10100 years. So, it is unlikely to happen anytime so.

Another reason not to worry about the vacuum decay model is to look at what the Universe is made of. It depends on the standard model being all there is to physics, but this isn’t the full picture.

We know this can’t be true because the standard model only explains 5% of the Universe.


There has to be other physics out there which might tell us a completely different story.

If we could understand dark matter and dark energy we could predict if the Universe was heading in another direction

5) Bounce

Professor Mack didn’t have time to do this section of the talk so what you are about to read is my poor attempt to explain what this Universe end will be.

The Big Bounce theory claims that the universe doesn’t have a beginning or an end. This means that our current Universe could have been formed after the collapse of a previous Universe and when our Universe dies it will cause a new universe to be created. These cosmological events would be repeated infinitely.  

Martin Bojowald, an assistant professor of physics at Penn State, first proposed the Big Bounce in 2007 in conjuction with his proposal of Loop Quantum Gravity. Loop Quantum Gravity, a theory being developed in the Penn State Institute for Gravitational Physics and Geometry, combines Einstein’s Theory of General Relativity with equations of quantum mechanics to create a mathematical description of the creation of the universe.


Martin Bojowald (born 18 February 1973 in Jülich) is a German physicist who now works on the faculty of the Penn State Physics Department, where he is a member of the Institute for Gravitation and the Cosmos. Prior to joining Penn State he spent several years at the Max Planck Institute for Gravitational Physics in Potsdam, Germany. He works on loop quantum gravity and physical cosmology and is credited with establishing the sub-field of loop quantum cosmology.

The Big Bang theory states that the universe originated from a singularity, a point in time where there was zero volume that contained infinite density and energy. The Big Bounce theory, however, proposes that there was a minimum volume that was not zero and a maximum energy that was not infinite. This miniscule mass exploded, as described in the Big Bang theory, and began to expand at astronomical speeds. The path of the universe after the explosion of the singularity mirrors the path described by the Big Bang. Galaxies were formed from small pieces of matter. These galaxies combined to form proto-galaxies, and the planets were formed by more pieces of matter pulled together by the gravity of stars.

Right now, our universe is in its expansion phase; this is the point that the Big Bounce theory diverges from the Big Bang theory. The Big Bang theory does not explain whether the universe will expand infinitely or reach a point of maximum expansion and collapse in upon itself, but the Big Bounce theory specifies that the universe will expand and then contract. The expansion is caused by the gravitational force between galaxies and the outward motion from the Big Bang, and after the universe reaches its maximum point of expansion and critical density, the density of the universe will increase and gravity within will cause the Big Crunch.

The Big Crunch is the period of contraction that will theoretically follow the point of maximum expansion. The universe will collapse, pulling in all matter and forming several black holes that will unify into one, enormous black hole. This black hole will collapse until the entire universe is a single point where the quantum effects of gravity are repulsive, and all of the conditions necessary for another Big Bang are met. The cycle will begin again when the point of mass explodes.

There could be lots of possibilities between a Big Bang and a crunch and another Big Bang.

Perhaps there would be heat deaths that would last different periods of time.

Perhaps there is a new evolution of the cosmos that we haven’t heard about.

There is still so much we don’t know.

Questions and answers

1) What is the Universe expanding into?

It may be just expanding without expanding into anything. We don’t have any evidence for an edge.

The stuff that makes up the Universe seems to be the same everywhere in every direction.

There is no evidence for space outside the Universe. All we see is that things in the Universe are getting further apart.

2) Are galaxies being stretched?

Probably not. Dark energy just moves apart things that are not gravitationally bound. It is just moving things apart not stretching space.

3) How are we sure that dark matter and dark energy exist?

A lot of effort has been put into explaining the Universe with tweaks of gravity and ignoring dark energy and dark matter. This has not worked.

When we look at the data, we don’t know why the expansion of the Universe is speeding up. But dark energy fits the data well. It explains a lot of things in the Universe.

We have a mathematical model and data and we see if the data matches the model. If it does then we go with it as long as it is useful.

There is a similar situation with dark matter. Stars are moving in such a way that there must be more matter than we can see.

Gravitational lensing is evidence that there is more matter.

A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer, that is capable of bending the light from the source as the light travels towards the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein’s general theory of relativity. (Classical physics also predicts the bending of light, but only half of that predicted by general relativity.),This%20is%20called%20gravitational%20lensing.

As the light emitted by distant galaxies passes by massive objects in the universe, the gravitational pull from these objects can distort or bend the light. This is called gravitational lensing.

Neutrinos are not heavy enough to be dark matter but they have similar properties.

A neutrino is a lepton and only interacts via the weak subatomic force and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The mass of the neutrino is much smaller than that of the other known elementary particles. The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected,

Dark matter might act through the weak nuclear force like neutrinos.

To tweak gravity to fit the data you would have to do something very strange to gravity that makes it mimic a new unseen particle of matter in every instance. Just a more complicated model that doesn’t fit the data so we go with more matter than we see rather than a bizarre tweak.

4) Could dark matter be gazillions of dark holes?

There are some possibilities for small dark holes to be dark matter.

Primordial black holes could act in the same way that dark matter is acting

Primordial black holes are a hypothetical type of black hole that formed soon after the Big Bang. In the early universe, high densities and heterogeneous conditions could have led sufficiently dense regions to undergo gravitational collapse, forming black holes.

There are certain mass ranges being ruled out as dark matter and some ranges where it isn’t so certain.

There aren’t any easy ways to make little black holes but we can’t entirely rule out that they are dark matter.

5) How can we discover more about dark matter and dark energy

We have lots of different avenues for dark matter. We can map out where it is by how it interacts with visible matter. How matter interacts with its gravity.

We can see how it is bending space and this gives us maps of where dark matter is. We have “seen” filaments of dark matter between galaxies,


A view of the distribution of dark matter in our universe, based on the Millennium Simulation. The simulation is based on our current ideas about the universe’s origin and evolution. It included ten billion particles, and consumed 343,000 cpu-hoursVirgo Consortium.

We hope to see dark matter interacting with matter in some noticeable way some day. Other than through gravity. Perhaps it interacts with the weak nuclear force.

There are a number of dark matter detectors that have been built. They are looking for an interaction between a dark matter particle and a detector that can’t be explained by cosmic rays.

Cosmic rays are high-energy protons and atomic nuclei which move through space at nearly the speed of light. They originate from the sun, from outside of the solar system, and from distant galaxies.

We are also looking for the possibility that dark matter particles would annihilate each other when they get too close and produce some matter we can see. So, we are looking for signatures of that in the centre of galaxies. We have seen hints that may or may not be that.

We are also trying to create dark matter in colliders like the LHC.

The Large Hadron Collider (LHC) is the world’s largest and highest-energy particle collider and the largest machine in the world. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries. It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.

The LHC is hoping that some of their proton collisions will produce dark matter. Less debris than the matter that went in.

Dark matter is a form of matter thought to account for approximately 85% of the matter in the universe and about a quarter of its total mass–energy density or about 2.241 x 10−27 kg/m3. Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts think that dark matter is abundant in the universe and that it has had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with the electromagnetic field, which means it doesn’t absorb, reflect or emit electromagnetic radiation, and is therefore difficult to detect.

6) How are we looking for dark energy?

It only makes the Universe expand faster. It seems to be uniform throughout the Universe and seems to be expanding equally in every direction. We can’t see it or interact with it.

We can map out the expansion history of it and we can map out the history of the growth of structures – clusters of galaxies – over time.

Some experiments that are being done could be scientifically related to certain types of dark energy.

Certain models for dark energy have evolved some interesting particle physics so we can look for things that can be associated with these models. So far, these experiments haven’t found anything in observations.

Everything is constant with dark energy being just the cosmological constant. It is just a property of space.

There is still work to be done on calculating the value of the cosmological constant as there are some issues in making it agree with what we know about quantum mechanics.

In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from supernovae measurements, which showed that the universe does not expand at a constant rate; rather, the expansion of the universe is accelerating. Understanding the evolution of the universe requires knowledge of its starting conditions and its composition. Prior to these observations, the only forms of matter-energy known to exist were ordinary matter, dark matter, and radiation. Measurements of the cosmic microwave background suggest the universe began in a hot Big Bang, from which general relativity explains its evolution and the subsequent large-scale motion. Without introducing a new form of energy, there was no way to explain how an accelerating universe could be measured. Since the 1990s, dark energy has been the most accepted premise to account for the accelerated expansion. As of 2020, there are active areas of cosmology research aimed at understanding the fundamental nature of dark energy.

7) Is vacuum decay related to the Big Bang? Was it some sort of vacuum decay?

Not the way we think about it.

There could have been vacuum decay transitions in the early Universe that could have produced some interesting phenomena. But not for the Big Bang this would have been a different process.

The Big Bang theory is a cosmological model of the observable universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from an initial state of extremely high density and high temperature, and offers a comprehensive explanation for a broad range of observed phenomena, including the abundance of light elements, the cosmic microwave background (CMB) radiation, and large-scale structure.

8) What is your opinion about the idea of a multiverse?

People have different views. Is it areas where there are different laws of physics?

Physicists do take it seriously.

We know about our observable Universe and we can what is going on in space, but that is not the entirety of space.

In larger space we can’t see if there are regions with very different properties to our part of the Universe.

In the early Universe cosmic inflation occurred, it could have caused many universes to come out of space in their own inflation events and created pocket universes with potentially different properties.

We will probably never be able to test these things.

People have looked to see our Universe colliding with another.

It is probable that we won’t be able to see further than our observable Universe.

We might find evidence if we can understand how the inflation era worked or if it even happened and what that would imply for larger space.

Related video

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