Cosmic timeline page added

cosmic_timeline.html

@@ -313,13 +313,67 @@ <h2>Cosmic timeline of the Universe</h2>
                 </section>
 
                 <section>
-                <h2 id="theoretical"></h2>
-
-
+                <h2 id="distance">overview of cosmology</h2>
+                The study of the universe's structure and evolution, highlighting key discoveries that connect large-scale cosmology with small-scale particle physics.
+
+                <ol>
+                    <li><b>Cosmology and the Universe: </b>The observable universe contains around \(10^{11}\) galaxies, each with billions of stars. The Milky Way, a spiral galaxy, is one of the larger galaxies with a diameter of about 100,000 light-years. The distances between galaxies are vast, measured in millions of light-years. For example, the Andromeda galaxy is 2 million light-years away.</li>
+                    <li><b>Hubble’s Discovery and the Expanding Universe: </b>Edwin Hubble's observations in the 1920s revealed that galaxies are moving away from each other, leading to the discovery of the universe’s expansion. Hubble's law (\(v = H_0 d\)) relates the velocity \(v\) of a galaxy’s recession to its distance \(d\), with \(H_0\) being the Hubble constant. This redshift, caused by the expansion of space, provides evidence of the Big Bang, a primordial explosion that occurred around 13-15 billion years ago.</li>
+                    <li><b>Distance Measurements: </b>Galaxies’ distances are measured using redshifts and standard candles like Cepheid variables. For example, a galaxy’s redshift allows astronomers to calculate how fast it is moving away, while its apparent brightness helps estimate distance. Observations of distant supernovae have suggested that the universe’s expansion might be accelerating rather than slowing down due to gravity.</li>
+                    <li><b>The Big Bang and Cosmic Microwave Background (CMB): </b>The Big Bang theory explains the current expansion and traces it back to a hot, dense state. As the universe cooled, it emitted radiation, now observed as the CMB. Discovered by Arno Penzias and Robert Wilson in 1964, the CMB is a key piece of evidence for the Big Bang, having a near-perfect blackbody spectrum at a temperature of 2.725 K. Small fluctuations in the CMB, first detected by COBE and later refined by WMAP, hint at the initial conditions that led to the formation of galaxies.</li>
+                    <li><b>Inflationary Scenario: </b>The theory of inflation, proposed by Alan Guth, suggests that the universe underwent an extremely rapid expansion (by a factor of \(10^{50}\)) in a fraction of a second (from \(10^{-35}\) s to \(10^{-32}\) s after the Big Bang). This expansion accounts for the universe’s smoothness, particularly the uniformity of the CMB.</li>
+                </ol>
 
 
 
                 </section>
+                <h2 id="distance">Distance measurments</h2>
+                Distance measurements in cosmology are crucial for understanding the structure and evolution of the universe. Several techniques are employed to determine distances to objects like stars and galaxies. The following mathematical approaches are key in cosmological distance measurements:
+                <ul>
+                    <li><b>Parallax Method (for nearby stars): </b>
+                        Parallax relies on the apparent shift in the position of a nearby star as observed from different points in Earth's orbit. The distance to the star, \( d \), is given by:
+
+                        \[
+                        d = \frac{1}{\theta}
+                        \]
+
+                        where \( d \) is in parsecs and \( \theta \) is the parallax angle in arcseconds. This technique is accurate for stars up to about 500 light-years away.
+                    </li>
+                    <li><b>Cepheid Variables (Standard Candles): </b>
+                        Cepheid variable stars exhibit a direct relationship between their luminosity and pulsation period. Once the absolute luminosity \( L \) of a Cepheid is known, the distance \( d \) to the star can be calculated using the inverse square law for brightness:
+
+                        \[
+                        d = \sqrt{\frac{L}{4 \pi F}}
+                        \]
+
+                        where \( F \) is the observed flux. This method extends to distances of millions of light-years and is vital for measuring distances to galaxies.
+                    </li>
+                    <li><b>Redshift and Hubble’s Law: </b>
+                        For distant galaxies, the cosmological redshift \( z \) is used as a proxy for distance. The redshift is related to the recession velocity \( v \) by:
+
+                        \[
+                        v = c z
+                        \]
+
+                        where \( c \) is the speed of light. Hubble’s Law provides a relation between the recession velocity and the distance \( d \) to the galaxy:
+
+                        \[
+                        v = H_0 d
+                        \]
+
+                        where \( H_0 \) is the Hubble constant. Combining these two equations gives:
+
+                        \[
+                        d = \frac{cz}{H_0}
+                        \]
+
+                        This relation is critical for determining distances to galaxies billions of light-years away.
+                    </li>
+                    <li><b>Supernovae Type Ia: </b>
+                        Supernovae Type Ia serve as standard candles for even greater distances. Their peak luminosity is known, so their distance can be determined using the same inverse square law of brightness used for Cepheid variables. This method is accurate for galaxies up to several billion light-years away and has been pivotal in studying the accelerating expansion of the universe.
+                    </li>
+                </ul>
+                These methods are essential tools in measuring cosmic distances and piecing together the vast scale of the universe.
 
                 <section>
 
@@ -336,13 +390,7 @@ <h2 id="theoretical"></h2>
                     <h2>References</h2>
                     <ul>
 
-                        <li>Chiral Plasma Instability and Primordial Gravitational waves, Sampurn Anad, Jitesh R. Bhatt & Arun Kumar Pandey <span><a href="https://arxiv.org/abs/1801.00650" target="_blank">[arXiv:1801.00650 [astro-ph.CO] (2019)]</a> Eur. Phys. J. C (2019) 79: 119.</span></li>
-
-
-                        <li>Gravitational waves in neutrino plasma and NANOGrav signal, Arun Kumar Pandey <a href="https://arxiv.org/abs/2011.05821" target="_blank">arXiv:2011.05821 [astro-ph.CO] (2020)</a>  [Eur.Phys.J.C 81 (2021) 5, 399]</li>
-
-                        <li><a href="https://www.americanscientist.org/article/gravitational-waves-and-the-effort-to-detect-them" target="_blank">Gravitational Waves and the Effort to Detect them</a>, By Peter Shawhan</li>
-
+                        <li><span><a href="https://courses.lumenlearning.com/suny-physics/chapter/34-1-cosmology-and-particle-physics/" target="_blank">Cosmology and Particle Physics.</span></li>
                     </ul>
                 </section>