The Crisis in Cosmology started recently but our wonderment at the sky started thousands of years ago. Humans have gazed up at the sky and wondered. The stars that illuminated the night sky seemed to have some order, and closer still, ancient peoples noticed the procession of planets, the sun and the moon had a definite order.
Today, we have developed sophisticated theories, models and technologies to understand our universe better. That is until we launched the James Webb Telescope and started to receive data that seemed to fly in the face of our current knowledge.
You may have heard there is a ‘crisis in cosmology’ from various news outlets, many of them fail to break down the problem and explain it in a digestible manner. So, what is the crisis in cosmology?
The Cosmological Constant
Any scientific theory or understanding is based on a fundamental truth.
For example, the theory of General Relativity by Albert Einstein, stipulates the need for space and time. Without assuming that space and time are prerequisite truths, the framework of General Relativity can not exist.
In the scientific community this is joked about using the expression ‘grant me a miracle and I will show you how the world works.’
All theories have their miracles so don’t think I have singled out Einstein. The big bang theory has something emerging from nothing and evolutionary theory has that life can arise from lifeless chemicals – commonly known as abiogenesis.
In the case of the Cosmological Constant, there are two miracles or fundamental truths it relies on – the theory of general relativity being correct, and that the universe is expanding.
The cosmological constant is the assumed rate of expansion in the universe. In simplest terms, how fast celestial bodies are moving away from us.
Lambda-CDM Cosmology
The model used to postulate the rate of the expansion in the Universe is Lambda-CDM.
Lambda-CDM posits that the rate of expansion from the Big Bang can be calculated if Cold Dark Matter exists. Lambda in the name represents dark energy as outlined in the theory of General Relativity. CDM stands for Cold Dark Matter.
This rate of expansion changes over time but does so in a consistent manner. Lambda-CDM counterintuitively states that the rate of expansion increases over time due to the effect of Cold Dark Matter.
With any model, observational evidence should bolster the model’s credibility. With Lambda-CDM there has been several pieces of observational evidence to suggest it is correct including:
- Evidence from the cosmic microwave background. This is a map created showing radiation from the early universe.
- Observations showing most galaxies (outside of the local cluster) moving away from us.
- Large scale distribution of galaxies supporting the predictions of the Lambda-CDM model.
To absolutely clarify, the Lambda-CDM model has been widely accepted as correct and has scientific consensus among cosmologists.
This consensus however is waning, and now a growing number of cosmologists are concerned they may have been wrong all along. Hence the crisis in cosmology. So, what has led to cosmologists changing their mind?
What is the Hubble Tension?
Despite being named after Edwin Hubble, the Hubble Law from which the Hubble Tension arises was actually deduced by Alexander Friedmann when he was working through equations related to Einstein’s General Relativity.
Hubble’s Law
Einstein had provided an overview of the operation of the universe but beyond his own equations, it opened the door for mathematicians and physicists to find new science. Einstein effectively created a framework, and others were able to fill in the gaps.
For example, Einstein did not believe black holes were possible, but they bore out in the maths of his theory and were discovered by Karl Schwarzschild.
Hubble’s law is much the same, discovered within the framework of General Relativity. The law states that objects in the universe move away at speeds equivalent to their distance from Earth.
The further away from Earth an object is, the faster it will move or retract from Earth.
The Hubble Tension
Hubble’s Law throws up a problem which is known as the Hubble Tension.
Essentially, depending on the method used to calculate the Hubble Constant (rate of expansion) scientists get different outcomes.
Using the Cosmic Microwave Background, it is estimated the rate of expansion of the universe is 67.7 km/s.
The ladder technique which we delve into below, yields a much faster rate of expansion of 73 km/s.
Over time, each way of measuring the Hubble Constant has been refined and the speed of expansion becomes more accurate for each method. The problem is these figures are very different across methods – creating the Hubble Tension.
The James Webb Space Telescope – Crisis in Cosmology
Amidst this chaos and disagreement about how to obtain the Hubble Constant, scientists were launching the James Webb Space Telescope, commonly shortened to the James Webb Telescope or just James Webb.
This telescope differs from other telescopes such as the Hubble Telescope because it records data in the infrared spectrum.
As light travels away from Earth it becomes redshifted. This means the light waves become stretched out over time and distance giving it a red hue.
James Webb is designed to capture this infrared light. In short, it is designed to see light from the furthest and oldest parts of the universe.
This design is amazing to say the least as you can see from the comparison between the Hubble Telescope and James Webb. James Webb is able to generate higher levels of detail by using the infrared spectrum on objects a great distance from Earth.
Why the James Webb Telescope is Causing Problems for Cosmology
When the first data arrived back from James Webb, scientists were puzzled.
One of the proposed solutions to the Crisis in Cosmology was to accept there was a problem in the way we were calculating the distance to other galaxies (see Ladder Method below).
Previously, telescopes would pick up a lot of light from distant galaxies making it hard to resolve individual features as shown in the Hubble telescope image above. This led scientists to believe this crowding of light was preventing us from accurately applying the ladder method.
James Webb though, with its ability to resolve features better using the infrared spectrum, showed crowding was not a factor in our calculations. In other words, it supported the Ladder Method.
The only serious alternative to measuring the expansion rate of the Universe is to use the Plank data and Cosmic Microwave Background, which is predicated on our fundamental understanding of physics being correct.
To summarise, James Webb observations pointed at our fundamental understanding of physics (General Relativity and by default any knowledge generated from the framework) being incorrect.
The Ladder Method – Crisis in Cosmology
Thus far I have spent a lot of time laying the groundwork.
We now know there is a disparity in results known as the Hubble Tension. We understand Lambda-CDM on a basic level and how it was arrived at using Einstein’s theory of General Relativity. And that at least until now, the Lambda-CDM model had good supporting evidence from observations.
Step in the Ladder Method also known as the Cosmic Distance Ladder, the way scientists calculate distances using a strict methodology. A method that has always provided a result that disagrees with the Lambda-CDM model to some extent.
As the name suggests, the Ladder Method is a step by step way of measuring the distance to celestial objects.
Ladder Method Step One
The first step of the ladder is to measure objects within distance we can see parallax. This is done by using Earth’s orbit of the sun to see the changes of an object compared to its background. We then triangulate the positions using Earth’s furthest distance from the sun as the base points of the triangle and the object we intend to measure as the final point.
Step in Pythagoras, and we can use his theorem to calculate distance.
Ladder Method Step Two – Crisis in Cosmology
At larger distances, the parallax becomes difficult to measure. To measure distances further we need to look at stars. Most commonly we use Variable Stars as they dim and brighten and enable easier measurement. But we can also look at static stars, compare them with stars comparable at known distances and then work out how far away they are by their apparent brightness.
Ladder Method Step Three
Step Two is fantastic for travelling out to a distance where parallax no longer works and we can see stars clearly, beyond that however, stars tend to be difficult to single out and therefore measure the distance to. Older galaxies appear to be a mess of light sources.
To measure at Step Three, we look for Type la Supernovas. These stars are exploding, and always reach around the same brightness as they explode. Because Supernovas are cataclysmic stellar events, it is possible to detect them even in the farthest reaches of the observable universe.
Why The Ladder Method May be Wrong
As I explained the Ladder Method you may have realised why it could be wrong. Common sense dictates it is a house of cards and if one assumption made in the process is wrong, the whole house collapses.
It is fair to say, the Ladder Method does rely on a lot of educated assumptions in order to generate a result. And the higher up the ladder, the margin of error grows because the rate of assumption increases.
Most cosmologists until James Webb started sending back results, believed there was no crisis, and the Ladder Method would be disproved and instead of redrawing the entire fundamental understanding of physics – they could create a better method to measure distance.
But James Webb is able to discern detailed data from the oldest galaxies, including some of the oldest stars. And the data it has sent back contradicts a lot of our understanding about physics in general. The data also supports the Ladder Method’s efficacy.
Why We Might Need New Physics – Crisis in Cosmology
Which means it is dawning on physicists and cosmologists alike that our fundamental understanding of the universe is missing at least a key component, perhaps even large swathes of understanding.
Some physicists believe that once we have unified quantum field theory and General Relativity the crisis of cosmology will be resolved.
The issue here is for decades now, physicists have been trying to work out a quantum state for gravity in order to marry the two theories together. Compounding this problem is that quantum gravity theories that are currently having the most success are those that do away with dark energy and dark matter – which is one of the miracles Lambda-CDM relies on.
It may be that we need to explore entirely new concepts in physics, which is exciting for amateurs such as myself looking in. For scientists who have built careers conforming to current theories by raising money and building reputations on those theories – it will probably be a prospect they will be dragged kicking and screaming toward.
It is for this reason, modern cosmologists and physicists are clinging so tightly to the sinking ship of Lambda-CDM and why the crisis in cosmology will only grow from here.