COSMIC SIGNS OF THE END TIMES

We are currently witnessing a fascinating competition between theory and experiment regarding dark energy: general relativity and experiments conducted to date favor the cosmological constant hypothesis; however, our "most advanced" fundamental theories, including gravity and quantum mechanics, clearly favor the option of a time-varying dark energy. Furthermore, the recent results of the DESI experiment, although still provisional, appear to favor a variable dark energy.

In this article, we will describe the consequences of this momentous competition, including the disturbing possibility that the destruction of the Universe has already begun and how this apocalyptic scenario might be detected.

Dark energy

The nature of 73% of the total energy in the Universe is unknown, which is why, in true Star Wars fashion, physicists and cosmologists call it dark energy. This energy is generally associated with the vacuum energy of space-time itself and can basically be of two types: a constant energy associated with a cosmological constant, or a variable energy associated with a new scalar field. The standard cosmological model and current measurements point to the former; however, most quantum gravity theories rule out the former and clearly point to the latter. Elucidating this problem is one of the most important questions in modern physics and cosmology, even more so after the DESI (Dark Energy Spectroscopic Instrument) experiment recently announced a certain tension between measurements and the standard cosmological model that could be resolved if dark energy were variable.

Incompatibility between fundamental physics and the cosmological constant

One of the strongest theoretical arguments to rule out a constant dark energy is the following: similarly to what happens during cosmic inflation the accelerated expansion of the Universe causes quantum field fluctuations to be amplified to macroscopic sizes. In fact, these amplified fluctuations during inflation gave rise to inhomogeneities that became the seeds of the galaxies we observe today. If we focus on the field structures and modes we observe in our current Universe and extrapolate them backward in time, we will arrive at the instant and distance at which these modes were created. By carrying out this process considering a constant acceleration, we would find that, starting at a certain age of the Universe, the distances at which these modes were created would be less than the Planck length. This would imply that, starting at a certain age of the Universe, macroscopic structures would begin to appear from fluctuations that were created at distances less than the minimum physically possible distance. This fact would have disastrous consequences for physics, as violations of unitarity .

During cosmic inflation, quantum field fluctuations were amplified and expressed as inhomogeneities in the cosmic microwave background. These inhomogeneities, through gravitational attraction, gave rise to the stars and galaxies we see today.

A more intuitive picture of this phenomenon is this: imagine a balloon inflating very rapidly. On the surface of the balloon, there are tiny dots so small we can't see them. These dots would correspond to quantum wavelength fluctuations the size of the Planck length. If the balloon were to continue inflating exponentially forever, these dots would become further and further apart. Over time, even dots smaller than those corresponding to the Planck scale would eventually separate so much that they would grow to enormous sizes and end up "frozen" as classical imperfections on the surface.

The censorship conjecture of transplackian modes

The problem we described in the previous section gives rise to the so-called transplackian censorship conjecture (TCC). The TCC conjecture can be defined as follows:

Where a(t) is the scale factor of the Universe, lpl is the Planck length, and H(t) is the Hubble parameter. This expression means that modes the size of the Planck length multiplied by the scale factor of the Universe corresponding to a certain time interval must always remain within the Hubble radius (1/H). If this were not the case, these modes would be amplified and would be found in classical structures of cosmological size. When would this happen?

This would happen in a time given by:

This time is about 140 times the current age of the Universe. Therefore, if the TCC condition is correct, the laws of fundamental physics do not allow the existence of a cosmological constant. (1)

The above time assumes a maximum lifetime of a Universe with constant accelerating expansion, which implies that before that time the Universe must transition to a new phase not dominated by a cosmological constant. This transition can occur in two main ways: either the Universe decays to another vacuum state of lower energy than the current one, or the vacuum potential, instead of settling into another lower vacuum state, continually "rolls" toward lower potentials, causing the dark energy potential to decrease over time (quintessence models).

Although it may seem incredible, in both cases there is a probability that the process of decay of the vacuum of our Universe has already begun:

-In the first case, although the probability of transition is very low, this possibility is always present. Furthermore, certain processes, such as the existence of low-mass primordial black holes, dramatically increase this probability.

-In the second case, if a cosmological acceleration were confirmed with a state parameter close to that of the cosmological constant but slightly lower, it would mean that the field driving dark energy is losing energy and is therefore already "rolling" down the downward potential slope. In this case, there could even be the possibility that the Universe could slow its expansion and begin to contract.

(see this article ).

Detecting the destruction of the Universe

We know from measurements made at the LHC that the Standard Model vacuum (the vacuum of our current Universe) is not stable and therefore there is a possibility that it could decay by tunneling into a more stable vacuum of lower potential. This would produce a bubble of true vacuum that would expand at almost the speed of light, destroying everything in its path. The probability of this happening in the short term is very low; however, if low-mass primordial black holes exist in the Universe, then they would act as "catalysts," dramatically increasing this probability (see, for example, this article ). In this scenario, there is even a possibility that the destruction of the Universe has already begun (2).

Next, we'll ask ourselves the following question: Is it possible to detect this bubble before it reaches Earth? Can science answer this question, or is this only possible in science fiction movie scripts?

The expanding true vacuum bubble has a lower vacuum potential than the rest of the Universe. This difference between the potentials inside and outside the bubble causes Higgs particles to be produced. These particles decay into photons and neutrinos with a characteristic energy that could be detected.

Modern science would allow us to detect the signs of the end of the Universe! (3)

If the true vacuum bubble were to expand at exactly the speed of light then there would be no possibility of detecting it, however, if this bubble contains a large number of Higgs particles these particles would interact with anything in their path (interstellar gas, radiation, etc.) and this interaction would slow down their expansion (4). For example, if the bubble were created at a distance of one million light years from Earth, with only a slowdown of 1 km/s the signal would reach us 3 years before the bubble.

The Higgs decay channels into fermions (table 1) and bosons (table 2)

are the following:

We would be interested in the decay channels into photons (gamma rays) and neutrinos (mu) since these are the easiest processes to detect. Taking these values into account, the energy density emitted per unit volume of the bubble would be:

Energy density spectrum of photon radiation from the bubble

!

Neutrino radiation energy density spectrum of the bubble

Due to relativistic effects this energy density must be corrected by a factor:

Where d is the distance from Earth to the bubble and z is the corresponding redshift.

Therefore, if one day we point our gamma ray or neutrino detectors towards outer space and record radiation with the energy spectrum of the figures above, we could be witnessing the signs of the end of the Universe!

Notes:

(1) Although the TCC conjecture is based on solid physical principles, its validity remains a matter of debate. Future work should confirm or reject the conjecture.

(2) Fortunately, the probability of a transition to a false vacuum remains very low even if primordial black holes existed. Furthermore, the theoretical uncertainties surrounding work on primordial black holes as catalysts for this transition are very large.

(3) In practice, the detection of this radiation from the bubble would be very complicated. Furthermore, if the bubble reached speeds very close to that of light, this radiation would be undetectable.

(4) The density of matter and radiation in cosmic space is extremely low so it is not very clear that their interaction with the bubble can have appreciable effects.

Sources:

The Signals of the Doomsday , Why DESI results should not be a surprise