The topic of today concerns the lifetime of the universe and how it could be calculated in the context of the Standard Model of particle physics (the theory that describes how all elementary particles behave).
[image credits: pixabay]
Everyday, one of the first thing I do (after coffee) is to browse the scientific articles connected to my field that appeared during the night (we have a dedicated website for this). I often found one or two interesting papers that may be worthy to read.
And sometimes, I report on this blog one of these interesting topics. The article of today falls in this category.
A HIGGS BOSON INTERACTING WITH ITSELF
Before starting, let me recall some basic facts about the Higgs boson.
[image credits: the particle zoo]
One of the key parameters of the Standard Model is the strength of the interaction of the Higgs boson with itself (you know, the guy from the plush on the right).
Yep, the Higgs boson not only interacts with all the elementary particles, but also with itself (and we can even have four of them involved).
Although this parameter could be calculated using the theory, it is important to double check that the predicted value matches the measurements. This ensures that we do not have any fancy new phenomenon.
However, the LHC will only be able to get a rough idea of the magnitude of the Higgs boson self-interactions. Even with all the data to be collected during the next 20 years! Equivalently, measurements will not be able to rule out possibly large deviations from the Standard Model value for the next 20 years!
But why is this important for the lifetime of the universe? We will see below!
QUANTUM TUNNELING
Still before starting, I will take 1 minute to discuss one important concept: quantum tunneling.
[image credits: pixabay]
To understand how this works, let us imagine a wall, and a tennis ball that one throws towards it. What can happen next? Well, the tennis ball will hit the wall, and bounce back. We can try a second time, no change. And again. And one billion times later… again.
Now, the microscopic world is governed by quantum mechanics and not classical mechanics. Without entering computational details, the probability that our microscopic quantum tennis ball does not bounce back, but goes through the wall,… is non-zero!
In fact, if we forget the analogy, a particle can pass (or tunnel, as currently said) through a potential barrier although at the classical level, this would not be possible.
This may sound weird. However, this is well studied and understood both theoretically and experimentally. There are even practical applications of quantum tunneling, like the tunneling microscope.
Now, time to go back to the topic.
TUNNELING BETWEEN POTENTIAL MINIMA? [harder part of the post]
What a title, isn’t it? There is a third and last important concept to introduce.
Without using too many complex words, the fate of the universe is connected to the potential of the Higgs boson, or the equation describing the dynamics (propagation, mass, interactions) of the Higgs boson.
In classical mechanics, we have potentials, and what is going on is related to the fact that one lies in the minimum of the potential. In the Standard Model, it is the same thing: we live in a minimum of the Higgs potential.
A potential may however have several minima, which is the (not so) funny part: the universe could catastrophically tunnel out of the current minimum in which it lies to another one that is more stable! Equivalently, the universe could cataclysmically collapse!
And now you get to the point: in order to calculate the lifetime of the universe, it is enough to calculate when and whether this tunneling occurs.
The only complication is that the calculation must be performed in the quantum field theory context, i.e., where we add field theory and special relativity on top of quantum mechanics.
Such a computation was so hard that no one succeeded… until now. The breakthrough of the paper I am talking about is that the authors managed to do this calculation exactly for the first time, handling all issues and unsolved challenge (with the proofs)!
This calculation in particular includes the properties of all the elementary particles, of course, like the self-interactions of the Higgs boson above-mentioned.
RESULTS: CONNECTING THE UNIVERSE FATE TO THE HIGGS BOSON
I will skip any technical detail (if you want them, please read the 70-pages long paper) and go straight to the results.
The authors calculated that the lifetime of the universe is between 1088 years and 10241 years. The huge uncertainty is due to a couple of parameters of the Standard Model that are not measured precisely enough and to some uncertainties inherent to the calculation.
[image credits: pixabay]
Funnily enough, they have additionally found that the way in which the Higgs boson interacts with itself is crucial. Yes, the parameter that has not been measured yet!
A modification of the magnitude of the Higgs boson self-interactions of 40% corresponds to changing the relevant parameter from -0.1 to -0.138. You may say, who cares, this is a small number anyhow.
Well, the universe cares a lot: it would have disappeared in 0.00000000000000000001 second after the big bang!
TAKE-HOME MESSAGE AND REFERENCES
In this post, I have described a scientific article that I have recently read. This article addresses the fate of the universe and the time it would need to collapse.
Three researchers have managed to perform the associated calculation in the Standard Model, and they have found that it is very long. In short, we are fine, except if the Standard Model is not the end of the story. In this case, we may or may not be fine.
A striking example of a drastic reduction of the universe lifetime is when the interactions of the Higgs boson is modified. This could have led to the destruction of the universe in no time!
More information can be found in the scientific article available for free from the arxiv. If you are interested by quantum tunelling, I can recommend the associated Wikipedia page that is very good.
Do not hesitate to ask questions in the comments!
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