Kosminės Foninės Mikrobangų Spinduliuotės (KFS) Detali Struktūra

Detailed structure of cosmic background microwave (KFS)

Temperature anisotropies and polarization revealing information about early density fluctuations

Faint Glow from the Early Universe

Shortly after the Big Bang, the Universe was a hot, dense plasma of protons, electrons, and photons, in which interactions were constantly taking place. As the Universe expanded and cooled, about 380 thousand years after the Big Bang, the time was reached when protons and electrons could combine into neutral hydrogen - this recombination. As a result, the probability of photon scattering was significantly reduced. From then on, these photons began to propagate freely, forming cosmic microwave background radiation (CMB).

Penzias and Wilson discovered it in 1965 as almost uniform ~2.7 K radiation, which became one of the strongest confirmations of the Big Bang model. Over time, increasingly sensitive instruments revealed very small anisotropy (temperature variations of up to one part in 105), as well as polarization These subtleties mark the early Universe. density fluctuations marks – the seeds from which galaxies and clusters later grew. So the KFS detailed structure contains invaluable information about cosmic geometry, dark matter, dark energy, and primordial plasma physics.

2. KFS Formation: Recombination and Separation

2.1 Photon and Baryon Fluid

Up to about 380 thousand years after the Big Bang (for redshift z ≈ 1100) matter existed mainly in the form of free electrons, protons and helium nuclei and a plasma of photons. Photons interacted strongly with electrons (Thomson scattering). Such smooth photon–baryon coupling led to photon pressure partially resisted gravitational compression by causing acoustic waves (baryonic acoustic oscillations).

2.2 Recombination and Final Dispersion

When the temperature dropped to ~3000 K, electrons began to combine with protons to form neutral hydrogen, a process called recombination. Photons then scattered much less frequently, "disconnected" from matter and propagated freely. This moment is defined by the surface of the last scattering (LSS). The photons emitted then are now recorded as KFS, but after about 13.8 billion years of cosmic expansion have shifted their frequency into the microwave range.

2.3 Blackbody Spectrum

The KFS spectrum of a nearly ideal blackbody (precisely measured by COBE/FIRAS in the 1990s) with a temperature T ≈ 2.7255 ± 0.0006 K is an important indicator of the origin of the Big Bang. The very small deviations from the pure Planck curve indicate that the early Universe was extremely thermally balanced and had almost no significant energy "injections" after the separation.

3. Temperature Anisotropy: A Map of Primary Fluctuations

3.1 From COBE to WMAP and Planck: Increasing Resolution

  • COBE (1989–1993) discovered anisotropies ΔT/T ∼ 10-5 level, confirming temperature irregularities.
  • WMAP (2001–2009) refined the measurements to a resolution of ~13 arcminutes and revealed the structure of acoustic peaks in the angular power spectrum.
  • Planck (2009–2013) achieved even better resolution (~5 arcminutes) and observations in multiple frequency channels, thus ensuring unprecedented quality. He measured the KFS anisotropies up to high multipoles (ℓ > 2000) and constrained the cosmological parameters with extreme precision.

3.2 Angular Power Spectrum and Acoustic Peaks

Angular power spectrum, Cℓ, denotes the variance of the anisotropies as a function of the multipole ℓ. ℓ is related to the angular scale θ ∼ 180° / ℓ. Acoustic peaks arises in it due to the previously mentioned acoustic oscillations in the photon–baryon fluid:

  1. The first peak (ℓ ≈ 220): Associated with the fundamental acoustic mode. Its angular scale reflects the Universe geometry (curvature). The peak at ℓ ≈ 220 strongly suggests a close plane (Ωso ≈ 1).
  2. Other peaks: Information about the amount of baryons (increases odd peaks), the density of dark matter (affects the phases of oscillations), and the expansion rate.

Planck data, covering several peaks up to ℓ ∼ 2500, have become the “gold standard” for determining cosmic parameters to a percent level of accuracy.

3.3 Nearly Scale Invariant Spectrum and Spectral Index

Inflation forecast almost scale invariant the power spectrum of primary fluctuations, usually described by a scalar spectral exponent nsObservations show ns ≈ 0.965, slightly below 1, consistent with the slow-roll inflation scenario. This strongly supports an inflationary origin for these density perturbations.

4. Polarization: E-modes, B-modes and Reionization

4.1 Thomson Scattering and Linear Polarization

When photons scatter into electrons (especially near recombination), any quadrupole the unevenness of the radiation field at that scattering location creates linear polarizationThis polarization is decomposed into E-mode (gradient) and B-mode (vortex). E-modes usually arise from scalar (density) perturbations, while B-modes can be created from gravitational lensing E-modes or from primordial tensor (gravitational wave) modes generated during inflation.

4.2 E-mode Polarization Measurements

WMAP the first one clearly recorded the polarization of E-modes, and Planck These measurements were further refined by allowing a better estimate of the optical depth of reionization (τ), thus refining the timing of when the first stars and galaxies reionized the Universe. E-modes are also related to temperature anisotropies, allowing for more precise parameterization and reducing uncertainties in matter density and cosmic geometry.

4.3 Hope to Detect B-mode

B-mode, created by lensing, have already been detected (at smaller angular scales), and this is consistent with theoretical predictions of how large-scale structure distorts E-modes. Meanwhile primordial gravitational waves (from inflation) B-modes on large scales have still not emerged. Many experiments (BICEP2, Keck Array, SPT, POLARBEAR) have provided upper limits on r (the ratio of tensor to scalar). If primordial B-modes with significant magnitude are ever detected, it would be a strong evidence for inflationary gravitational waves (and GUT-level physics). The search continues with future instruments (LiteBIRD, CMB-S4).

5. Cosmological Parameters from KFS

5.1 ΛCDM Model

A minimum of six parameters is usually applied to KFS data. ΛCDM model:

  1. Physical baryon density: Ωb h²
  2. Physical density of cold dark matter: Ωc h²
  3. Angular size of the sound horizon during recombination: θ* ≈ 100
  4. Reionization optical depth: τ
  5. Scalar disturbance amplitude: As
  6. Scalar spectral index: ns

According to Planck data, Ωb h² ≈ 0.0224, Ωc h² ≈ 0.120, ns ≈ 0.965, As ≈ 2.1 × 10-9Overall, the KFS data strongly suggest a planar geometry (Ωso=1±0.001) and a nearly scale-invariant power spectrum consistent with inflation theory.

5.2 Additional Restrictions

  • Neutrino mass: From KFS lensing, it is possible to somewhat constrain the total sum of neutrino masses (current limit ~0.12–0.2 eV).
  • Effective number of neutrino species (Neff): sensitive to the amount of radiation. Observed value Neff ≈ 3.0–3.3.
  • Dark energy: At high redshifts (early times), the CFS mainly reflects the dominance of matter and radiation, so direct constraints on dark energy require matching with BAO, supernova, or lensing data.

6. Solutions to Horizon and Plane Problems

6.1 The Horizon Problem

Without early inflation, distant regions of the KFS (~180° apart) would not be able to communicate causally, yet they have nearly the same temperature (with a difference of 1 in 100,000). The homogeneity of the KFS reveals horizon problemDuring inflation, a sudden exponential expansion resolves it, significantly enlarging the area that was originally in causality and extending it beyond the current horizon.

6.2 Planarity Problem

KFS observations show that the geometry of the Universe is extremely close to flat (Ωso ≈ 1). In a normal non-inflationary Big Bang, even small deviations from Ω=1 would grow very large over time – the Universe would have become curvature-dominated or collapsed. Inflation, by expanding space (e.g., 60 e-rays), effectively “straightens” the curvature, pushing Ω→1. The first acoustic peak at ℓ ≈ 220 perfectly confirms this near-flat scenario.

7. Current Tensions and Unanswered Questions

7.1 Hubble Constant

Although according to KFS based The ΛCDM model yields H0 ≈ 67.4 ± 0.5 km/s/Mpc, local distance ladder measurements indicate higher values ​​(~73–75). This "Hubble voltage" may indicate unobserved systematic errors or new physics beyond the usual ΛCDM (e.g. early dark energy, additional relativistic particles). There is no consensus yet, so the debate continues.

7.2 Large-Scale Anomalies

Some of the large-scale anomalies in the KFS maps, such as a "cold spot", a small quadrupole or a small dipole arrangement, may be random statistical anomalies or subtle hints of cosmic topology and new physics. The Planck data do not show clear evidence for large-scale anomalies, but this area remains under investigation.

7.3 Missing B-modes from Inflation

In the absence of large-scale B-mode detection, we have only upper limits on the amplitudes of inflationary gravitational waves, which constrain the energy scale of inflation. If the B-mode signature is undetectable well below the current limits, some large-scale inflation models become unlikely, perhaps indicating lower-energy or alternative inflationary physics.

8.Upcoming KFS Projects

8.1 Ground-based Experiments: CMB-S4, Simons Observatory

CMB-S4 – the next significant generation of ground-based experiments (planned for the 2020s–2030s) aimed at firmly detecting or strictly constraining the primary B-modes. Simons Observatory (in Chile) will record temperature and polarization at various frequencies, allowing for precise filtering of foreground background interference.

8.2 Satellite Projects: LiteBIRD

LiteBIRD (Japan's JAXA) - proposed space mission for large-scale polarization measurements, capable of determining (or constraining) the tensor-scalar ratio r to ~10-3If successful, it would either demonstrate inflationary gravitational waves or severely constrain inflation models that predict a higher value of r.

8.3 Interaction with Other Measurement Methods

Joint analyses of the KFS lensing, galaxy mass distribution, BAO, supernovae, and 21 cm data will allow for more precise estimates of the history of cosmic expansion, neutrino masses, testing the laws of gravity, and possibly discovering new phenomena. This interaction ensures that the KFS remains a reference data set, but not the only one, for answering fundamental questions about the structure and evolution of the Universe.

9. Conclusion

Cosmic microwave background radiation – this is one of the most amazing of the early Universe "fossils". Her temperature anisotropy, seeking several dozen µK, saves primary density fluctuations – imprints that later grew into galaxies and clusters. Meanwhile polarization data show reionization features, acoustic peaks even more accurately and open up possibilities for observing primordial gravitational waves from inflation.

From COBE, WMAP to Planck observations, our resolution and sensitivity have grown dramatically, culminating in a precisely refined ΛCDM model. However, there are still uncertainties – such as the Hubble tension or the as-yet-undetected inflationary B-modes – which suggest that even deeper answers or new physics may lie ahead. Future experiments and new combinations of data with surveys of large-scale structures promise new discoveries – perhaps confirming the detailed mosaic of inflation or revealing unexpected twists. Via KFS detailed structure We see the earliest moments of cosmic evolution – from quantum fluctuations at Planck energies to the magnificent networks of galaxies and clusters observed billions of years later.

Literature and Additional Reading

  1. Penzias, AA, & Wilson, RW (1965). "A Measurement of Excess Antenna Temperature at 4080 Mc/s." The Astrophysical Journal, 142, 419–421.
  2. Smoot, G. F., et al. (1992). "Structure in the COBE differential microwave radiometer first-year maps." The Astrophysical Journal Letters, 396, L1–L5.
  3. Bennett, C. L., et al. (2013). "Nine-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: Final maps and results." The Astrophysical Journal Supplement Series, 208, 20.
  4. Planck Collaboration (2018). "Planck 2018 results. VI. Cosmological parameters." Astronomy & Astrophysics, 641, A6.
  5. Kamionkowski, M., & Kovetz, ED (2016). "The Quest for B Modes from Inflationary Gravitational Waves." Annual Review of Astronomy and Astrophysics, 54, 227–269.
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