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Why Scientists Say the Universe is 13.8 Billion Years Old

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Why Scientists Say the Universe is 13.8 Billion Years Old

Why Scientists Say the Universe is 13.8 Billion Years Old

Key Takeaways

  • The Universe is estimated to be 13.8 billion years old, based on measurements of the cosmic microwave background, the expansion rate of the Universe, and the age of the oldest known stars.
  • Two primary methods for determining the Universe’s age involve dating the oldest objects and applying general relativity to the expanding Universe.
  • The Hubble tension, a discrepancy between different measurements of the Universe’s expansion rate, poses a challenge to the current age estimate but does not significantly alter it.
  • Cosmic inflation, a rapid expansion before the hot Big Bang, suggests that the Universe could be older than 13.8 billion years, but this remains speculative.
  • The age of the Universe is a crucial aspect of modern cosmology, providing insights into the origins and ultimate fate of the cosmos.
Why Scientists Say the Universe is 13.8 Billion Years Old
The globular cluster Messier 69 is very old. It formed when the Universe was just 5% of its current age, making it about 13 billion years old. Despite its age, it has a high metal content, with metals at 22% of what we find in our Sun. In Messier 69, the brighter stars are in the red giant phase. This means they are running out of fuel in their cores. There are also a few blue stars. These blue stars are called blue stragglers. They form from the merging of other stars. (Credit: Hubble Legacy Archive (NASA/ESA/STScI))

The Hot Big Bang Theory: The Universe’s Beginning?

The theory of the hot Big Bang suggests that the Universe had a definitive beginning, often described as “a day without a yesterday.” This idea, once controversial and mind-boggling, is now a cornerstone of modern cosmology. The concept of a beginning to the Universe aligns with some religious texts, causing skepticism among certain circles. However, from a scientific perspective, the hot Big Bang is not the absolute start of the Universe but rather the aftermath of a preceding epoch, possibly cosmic inflation.

Despite this nuance, when asked about the age of the Universe, cosmologists and astrophysicists consistently respond with “13.8 billion years.” This figure has been reached through various methods, including the analysis of the CMB and the study of distant galaxies and star clusters. But where do we start counting the Universe’s age, and what are the implications of this starting point?

Why Scientists Say the Universe is 13.8 Billion Years Old
The life cycles of stars can be understood using the color/magnitude diagram shown here. As stars get older, they leave the diagram. This helps us figure out the age of a star cluster. The oldest globular star clusters, like the very old cluster shown on the right, are over 13 billion years old. But many globular clusters also have a second, younger group of stars. This shows that these clusters had more than one period of star formation. (Credit: Richard Powell (L), R.J. Hall (R))

Measuring the Universe’s Age: Two Main Methods

There are two primary approaches to determining the age of the Universe:

  1. Dating the Oldest Objects: By measuring the age of the oldest stars or star clusters, we can establish a lower bound for the Universe’s age.
  2. Cosmic Expansion and General Relativity: By applying our understanding of general relativity and the known components of the Universe, we can calculate the time elapsed since the hot Big Bang.
Why Scientists Say the Universe is 13.8 Billion Years Old (8)
In the top panel, our modern Universe has the same properties everywhere. This includes temperature. These properties originated from a region with the same characteristics.
In the middle panel, space could have had any curvature. Inflation made the space expand so much that we can’t see any curvature today. This solves the flatness problem.
In the bottom panel, high-energy relics existed before. Inflation pushed these relics away. This solves the high-energy relic problem.
These examples show how inflation solves three major puzzles. The Big Bang alone cannot explain these puzzles. (Credit: E. Siegel/Beyond the Galaxy)

Method 1: Dating the Oldest Objects

As cosmology evolved from astronomy and physics, one of the first reliable methods for estimating the age of the Universe involved studying the oldest stars and star clusters. Globular clusters, in particular, are dense groups of stars that formed early in the Universe’s history. These clusters are invaluable for estimating the age of the Universe.

Globular clusters contain stars of varying masses, colors, and lifespans. The most massive and brightest stars exhaust their nuclear fuel quickly, leaving behind only cooler, dimmer stars. By studying these remaining stars and the absence of their massive counterparts, scientists can estimate the age of the cluster, which often exceeds 12 billion years. This method provides a lower bound for the Universe’s age, confirming that it must be at least as old as the oldest stars, around 12.5 to 13 billion years.

Method 2: Cosmic Expansion and General Relativity

The second method involves applying general relativity to the expanding Universe. The Friedmann equations, derived from Einstein’s general relativity, describe how the Universe expands over time. By inputting data such as the current expansion rate (known as the Hubble constant) and the composition of the Universe, scientists can calculate how long it has been expanding since the hot Big Bang.

Why Scientists Say the Universe is 13.8 Billion Years Old (8)
Blue and red lines show a “traditional” Big Bang scenario. In this view, everything starts at time t=0. This includes spacetime itself.
In an inflationary scenario, shown in yellow, we never reach a singularity. A singularity is a point where space is infinitely small. Instead, space just becomes very small in the past while time keeps going backward forever.
The last tiny fraction of a second, from the end of inflation, leaves its mark on our observable Universe today.
At the start of the hot Big Bang, the size of the now-observable Universe could not have been smaller than about 1 cubic meter in volume.
(Credit: E. Siegel)

The most accurate data for this calculation comes from the CMB, the remnant radiation from the Big Bang, and large-scale galaxy clustering. The Universe’s composition is primarily:

  • 68% dark energy
  • 27% dark matter
  • 4.9% normal matter
  • 0.1% neutrinos
  • 0.01% photons

Given these proportions and an expansion rate of 67 km/s/Mpc, the calculations yield an age of approximately 13.8 billion years. However, this conclusion is not without contention.

Why Scientists Say the Universe is 13.8 Billion Years Old
By looking back in time and distance from today, we can learn about how the Universe will change in the future. We do this by finding a connection between how fast the Universe is expanding and the amount of matter and energy it has. When we measure the expansion rate, we can guess how long it’s been since the hot Big Bang started.
In the late 1990s, data from exploding stars called supernovae showed something surprising. The data suggested that the Universe has a lot of dark energy, not just matter and radiation. This was a new discovery. (Credit: Saul Perlmutter/UC Berkeley)

The Hubble Tension: A Challenge to the Age of the Universe?

One of the most significant challenges to the current estimate of the Universe’s age is the so-called Hubble tension. This discrepancy arises because different methods of measuring the Hubble constant (the Universe’s expansion rate) yield slightly different values. Early Universe measurements, like those from the CMB, suggest a rate of 67 km/s/Mpc, while late-time methods, such as the cosmic distance ladder, indicate a higher rate of around 73-74 km/s/Mpc.

If the higher rate is correct, it could imply a younger Universe, possibly around 13.6 billion years. However, the relationship between the expansion rate, dark energy, and dark matter introduces complexities. A faster expansion rate would require adjusting the proportions of dark energy and dark matter, slightly lowering the Universe’s age but not drastically altering it. Even with this adjustment, the difference is marginal, reinforcing the robustness of the 13.8 billion-year estimate.

Why Scientists Say the Universe is 13.8 Billion Years Old
This graph shows the values of the Hubble constant on the left, which is the y-axis. These values best fit the data from the cosmic microwave background. The cosmic microwave background is the leftover radiation from the Big Bang. Data comes from three sources: ACT, ACT + WMAP, and Planck. A higher Hubble constant is allowed. However, this means the Universe would have more dark energy and less dark matter. (Credit: ACT Collaboration DR4)

Cosmic Milestones: When Should We Start Counting?

Another intriguing question is when to start counting the Universe’s age. The CMB, which we observe today, was emitted 380,000 years after the Big Bang when the Universe cooled enough for neutral atoms to form. But should we start counting from this point, or should we go back further to earlier milestones?

Several significant events occurred before the CMB was emitted, such as Big Bang nucleosynthesis (which took place just minutes after the Big Bang) and the formation of the cosmic neutrino background, which imprinted itself when the Universe was just one second old. These events suggest that counting should start even earlier than the CMB, although the difference is negligible in the context of 13.8 billion years.

Why Scientists Say the Universe is 13.8 Billion Years Old
A visual history of the expanding Universe shows the hot, dense state known as the Big Bang. After the Big Bang, the Universe grew and formed structures. The whole set of data, including the observations of light elements and the cosmic microwave background, points only to the Big Bang as a valid explanation for everything we see. When the Universe expands, it also cools. This cooling allows ions, neutral atoms, and eventually molecules to form. Gas clouds, stars, and finally galaxies form as a result. (Credit: NASA/CXC/M. Weiss)

The Role of Cosmic Inflation: What Came Before the Big Bang?

One of the most fascinating aspects of modern cosmology is the realization that the hot Big Bang may not have been the true beginning. Before the Big Bang, the Universe likely underwent a period of cosmic inflation, a rapid expansion driven by a high-energy state. This inflation smoothed out any irregularities and set the stage for the Big Bang.

Why Scientists Say the Universe is 13.8 Billion Years Old (8)
Inflation started from a pre-existing state. It predicts that many independent universes will form as inflation continues. Each universe will be completely separate, with more inflating space in between. One of these “bubbles,” where inflation ended, created our Universe about 13.8 billion years ago. Today, dark energy dominates our Universe. It causes space to expand very quickly. These scenarios might be related. However, we do not know how long inflation lasted before the hot Big Bang. We can only say “at least 10^-32 seconds.” (Credit: Nicolle Rager Fuller)

If cosmic inflation preceded the Big Bang, then the Universe’s true age could be even greater than 13.8 billion years. However, the duration of inflation is uncertain, and it could have lasted for an extraordinarily brief time. Thus, the age of the Universe is conventionally measured from the start of the hot Big Bang, as this is the earliest Era we can confidently describe using known physics.

The Universe’s age of 13.8 billion years is a well-supported estimate based on multiple lines of evidence. From the oldest stars to the cosmic microwave background and the expansion of space itself, all indicators converge on this figure. While there are challenges and differences, such as the Hubble tension and the role of cosmic inflation, the fundamental conclusion remains robust.

Why Scientists Say the Universe is 13.8 Billion Years Old (8)
If these three different regions of space couldn’t thermalize, share information, or transmit signals to one another, then why are they all the same temperature? Thermalize means to reach the same temperature. This is a problem with the initial conditions of the Big Bang. How could these regions all have the same temperature unless they started that way somehow? (Credit: E. Siegel/Beyond the Galaxy)

Whether the Universe’s true beginning was the hot Big Bang or an earlier inflationary phase, the age of 13.8 billion years remains a cornerstone of modern cosmology. This understanding not only informs us about the past but also provides a foundation for exploring the Universe’s future and the ultimate fate of all that exists.

#UniverseAge, #Cosmology, #BigBang, #CosmicInflation, #HubbleTension, #DarkMatter, #DarkEnergy, #GeneralRelativity, #Astrophysics, #ScienceExplained

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Black Holes and Space: Can Black Hole Mergers Reveal Hawking Radiation?

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Journey into the black hole. Space shuttle flies straight into black holes singularity with lens flare. 3D render illustration. Elements of this image were furnished by NASA. Black Holes and Space: Can Black Hole Mergers Reveal Hawking Radiation?

Black Holes and Space: Can Black Hole Mergers Reveal Hawking Radiation?

Key Takeaway

A new theory suggests that tiny black holes, called “morsel” black holes, created during the merger of larger black holes might be the key to finally detecting Hawking Radiation.

Summary

  • Hawking Radiation is a theory that black holes emit radiation over long periods of time, but it has never been observed.
  • Researchers believe that black hole mergers may create small black holes called “morsel” black holes.
  • The Hawking Radiation from these morsel black holes is predicted to be much stronger and easier to detect due to their small size.
  • This radiation would produce a specific kind of gamma ray burst with high-energy photons.
  • Existing telescopes like HAWC Gamma-ray observatory might be able to detect these gamma rays.
  • Some challenges remain, such as the morsel black holes’ environment during emission potentially affecting the radiation and limitations in our understanding of physics at high energies.
  • If detected, this Hawking Radiation could reveal new physics beyond our current knowledge.
  • The existence of these morsel black holes themselves could also be a sign of dark matter, leftover from the early universe.
This is a simulation of merging supermassive black holes. The credit goes to NASA's Goddard Space Flight Center and Scott Noble. Black Holes and Space
This is a simulation of merging supermassive black holes. The credit goes to NASA’s Goddard Space Flight Center and Scott Noble.

Black Hole Burps: Could Tiny Holes Finally Reveal Hawking Radiation?

Black holes are enigmatic giants, warping spacetime with their immense gravity and shrouding themselves in an event horizon, a point of no return for even light. One of the biggest mysteries surrounding them is Hawking Radiation, a theory proposed by Stephen Hawking in the 1970s. This theory suggests that black holes, despite their immense gravity, slowly leak energy and particles over vast stretches of time, eventually evaporating entirely.

The problem? Hawking Radiation is incredibly weak, especially for stellar-mass black holes, making it nearly impossible to detect directly. Here’s where things get interesting. A recent study published in a paper titled “Measuring Hawking Radiation from Black Hole Morsels in Astrophysical Black Hole Mergers” proposes a fascinating new way to observe this elusive phenomenon.

The study hinges on the idea of “morsel” black holes, theorized tiny black holes created during the violent mergers of larger black holes. These mergers, first predicted and then confirmed through gravitational wave detections, are incredibly energetic events. Researchers believe that these mergers might also eject a number of these morsel black holes, some as small as asteroids.

The key here is size. Because Hawking Radiation is inversely proportional to mass, these tiny black holes would emit Hawking Radiation at a much stronger rate compared to their larger counterparts. This stronger radiation is predicted to manifest as a specific kind of gamma-ray burst with high-energy photons.

The good news? Existing gamma-ray telescopes like the HAWC Gamma-ray Observatory might be powerful enough to detect these unique gamma-ray signatures. This opens up a new window for finally observing Hawking Radiation and validating a cornerstone of theoretical physics.

However, there are still challenges to overcome. The intense gravitational environment during a black hole merger could affect the Hawking Radiation emitted by the morsel black holes. Additionally, our current understanding of physics at extremely high energies might have limitations, making it difficult to precisely predict the radiation’s characteristics.

Even with these challenges, the prospect of detecting Hawking Radiation is a scientific game-changer. Not only would it confirm a major prediction by Stephen Hawking, but it could also shed light on new physics beyond our current knowledge. The study mentions that the properties of the gamma-ray bursts could reveal new forces or particles not yet accounted for in the Standard Model.

The existence of the morsel black holes themselves is also intriguing. Some researchers speculate that these tiny black holes, leftovers from the early universe with different physical conditions, could be a form of dark matter, the mysterious substance that makes up a significant portion of the universe’s mass.

The ongoing quest to understand black holes might soon yield groundbreaking discoveries, with these tiny morsel black holes playing a crucial role in unveiling the secrets of Hawking Radiation and the fundamental nature of the universe.

Sources: 

  1. CERN (European Organization for Nuclear Research): “Supersymmetry.” Available at: https://www.home.cern/science/physics/supersymmetry
  2. Department of Energy: “The Standard Model of Particle Physics.” Available at: https://www.energy.gov/science/doe-explainsthe-standard-model-particle-physics
  3. HAWC Observatory: Available at: https://www.hawc-observatory.org/
  4. Wikipedia: “Hawking radiation.” Available at: https://en.wikipedia.org/wiki/Hawking_radiation
  5. ArXiv: “Title of the paper.” Available at: https://arxiv.org/abs/2405.12880

Hastags:

#HawkingRadiation, #BlackHoles, #BlackHoleMergers, #DarkMatter, #GammaRays, #Astrophysics, #Cosmology, #UniverseToday, #MorselBlackHoles, #NewPhysics
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Ultralight Black Holes Beyond Death’s Reach: Exploring the Possibility

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Ultralight Black Holes Beyond Death's Reach Exploring the Possibility

Ultralight Black Holes Beyond Death’s Reach: Exploring the Possibility

Key Takeaway

A new theoretical model proposes that the universe could be filled with ultralight primordial black holes that reach an equilibrium state or become naked singularities, offering a potential explanation for dark matter while evading current observational limitations.

Summary

  • The new work explores the idea of primordial black holes (PBHs) as a potential candidate for dark matter, focusing on ultralight black holes.
  • PBHs are hypothetical objects formed in the early universe from micro-fluctuations in matter density and spacetime.
  • While most PBH candidates have been ruled out by observations, ultralight black holes could evade these constraints due to their small size and the effects of Hawking radiation.
  • The paper considers three possible outcomes for ultralight black holes:
    • Complete evaporation through Hawking radiation, resulting in a brief flash of high-energy particles.
    • Reaching an equilibrium state where evaporation is prevented.
    • Forming a naked singularity, where the event horizon disappears, leaving an exposed dense mass.
  • In the latter two cases, the remnants could have a net electric charge, potentially making them detectable by future neutrino detectors.
  • If the remnants are electrically neutral, they would be impossible to detect directly or through their decay, making the model essentially unprovable but consistent with observations.
  • The work suggests that primordial black holes cannot be entirely ruled out as a potential dark matter candidate until better observational data is available.
  • The model joins the theoretical pile of possibilities for dark matter, as the search for a conclusive solution continues.
Ultralight Black Holes Beyond Death's Reach Exploring the Possibility
Observational limits for primordial black holes.
Credit: S. Profumo

Could Ultralight Primordial Black Holes Solve the Dark Matter Mystery?

A new theoretical model proposes an intriguing idea: the universe may be full of ultralight primordial black holes. These black holes could reach a balance or turn into naked singularities. This bold theory could explain the mysterious dark matter and also avoids conflict with existing observational data.

Primordial black holes (PBHs) are theoretical objects believed to have originated early in the universe’s history. They may have formed from tiny variations in matter density and spacetime. These small black holes can vary in size from a grain of sand to the mass of a mountain. They have often been thought to be potential sources of dark matter. This is because they gather around galaxies and do not emit light.

Most PBH candidates are unlikely due to observations. These observations show that the large number of PBHs needed to explain dark matter would cause frequent microlensing flares. During these flares, PBHs pass in front of stars, making them appear brighter. Several sky surveys have looked for these flares but found none. As a result, the idea that PBHs make up dark matter has become less popular recently.

Explore the concept of ultralight black holes, a new angle on a classic theory. These hypothetical black holes are at the lighter end of the mass scale. Here, Hawking radiation becomes significant. Hawking radiation, named after the physicist Stephen Hawking, indicates that black holes emit particles and energy. This radiation leads to their eventual evaporation.

The decay rate from Hawking radiation is faster for smaller black holes. Thus, ultralight black holes might evaporate more quickly on a cosmic scale. However, our understanding of quantum gravity is not yet complete. Therefore, the precise outcome of these ultralight black holes is still unknown. This uncertainty is where the new model becomes relevant.

The paper explores three potential outcomes for ultralight black holes:

  1. Complete Evaporation: The black hole radiates away entirely, culminating in a brief flash of high-energy particles. While this scenario would add to the reheating effect of the early cosmos, no such flashes have been observed, casting doubt on this possibility.
  2. Equilibrium State: Some unknown mechanism prevents complete evaporation, and the black hole reaches an equilibrium state, potentially with a net electric charge.
  3. Naked Singularity: Similar to the second outcome, the black hole reaches an equilibrium state, but in this case, the event horizon disappears, leaving behind an exposed dense mass known as a naked singularity, which could also carry a net electric charge.

If the last two scenarios occur, the remains of these ultralight black holes might have an electric charge. This charge would allow the next generation of neutrino detectors to possibly find them. On the other hand, if these remains lack electric charge, they would be almost impossible to detect. They wouldn’t decay into other particles, nor would they be big enough to observe directly.

An undetectable scenario may not be satisfying scientifically, but it matches current observations. It also keeps the idea that ultralight primordial black holes could be a form of dark matter viable. Until better data is collected or our understanding of quantum gravity improves, this concept remains one of many theories in the search to solve the dark matter mystery.

HASHTAGS:

#DarkMatter, #PrimordialBlackHoles, #HawkingRadiation, #UltralightBlackHoles, #QuantumGravity, #Astrophysics, #CosmicMysterySolution, #NakedSingularities, #NeutrinoDetectors, #TheoryOfEverything #Ultralight Black Holes

Source: arXiv Link: Read the paper

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