cosmology - Failure of the Steady State Theory

I was reading a journal of astronomy and came to the most famous opponent of Big Bang theory:

The Steady State Theory:

The 20th - century theory was proposed by Hoyle,Gold and Bondie. The theory is based on the Perfect Cosmological Principle which states that universe has no change in its appearance and is homogeneous. It is isotropic in nature. When an old star dies,new star replaces it. So everything remains the same . According to the theory, the universe has neither any beginning nor any end. Universe was and will always the same through the whole time.

Then I was surprised when the journal wrote that this theory has no scientific existence now. It is obsolete today. While reading this, I have found nothing wrong. Isn't the universe isotropic? Why did the Steady State theory fail?

Answer

Here is a good basic summary of the history of the steady-state theory and the observations that caused it to fall out of favor, mainly the second two mentioned by Kyle Kanos. One of these was the observation of intense radio sources that didn't seem evenly distributed throughout the universe, but were only seen at large distances (higher redshifts):

The program at Cambridge was led by Martin Ryle, who in 1974 would receive the Nobel Prize in physics for his overall contributions to radio astronomy. In 1951 Ryle believed that radio sources were located within our galaxy, and hence were of no cosmological interest. But over the next few years he became convinced that most of the radio sources he was detecting were extragalactic. His observations, then, could be used to test cosmological models. Ryle argued that his survey of almost 2,000 radio sources, completed in 1955, contradicted steady-state theory, because more distant/older sources seemed to be distributed differently from nearby ones. But he overstated the significance of his initial data. Only after more years of work would radio observations argue strongly against steady-state theory.

And the other was the blackbody spectrum of the cosmic microwave background radiation, which is naturally predicted by the Big Bang theory but not by the steady-state theory (Alpher and Herman had predicted it in the 1940s and the idea had been rediscovered by Robert Dicke and Yakov Zel'dovich in the early 1960s, all before its actual discovery in 1965):

In 1963 Arno Penzias and Robert Wilson, studying the sky's microwave "noise" for Bell Telephone Laboratories, realized that they had detected microwaves coming from all around the sky, a universal background radiation. Robert Dicke, a physicist nearby at Princeton University, learned of the measurement and in 1965 correctly interpreted it as radiation of about 3 degrees Kelvin, left over from the big bang. Dicke had not known about Alpher and Herman's prediction, and had independently thought of the cosmic background radiation. Even before learning of Penzias and Wilson's observation, Dicke had set his former student James Peebles to work on calculating the nature of this radiation. Only later was Alpher and Herman's predition recovered and appreciated.

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The minority who still preferred steady-state theory were not convinced that the big bang had been detected. Couldn't Penzias and Wilson's single observation have some other explanation? Hoyle argued that the radiation could come from interaction between stellar radiation and interstellar needle-shaped grains of iron. Only a number of measurements at different frequencies could confirm that the radiation had the properties predicted for a remnant of the big bang. It was not until the early 1970s that techniques advanced enough to make these measurements, bringing abundant confirmation.

For most purposes, however, the debate between the big bang and the steady state was over in 1965, with big bang the clear winner. Steady-state advocates were reduced to making ad hoc arguments of little plausibility, and they were increasingly marginalized.

This page goes into some more technical detail, and mentions another issue brought up in Godparticle's answer, that of the abundance of helium, which can be explained easily by Big Bang nucleosynthesis but not by the steady-state theory:

The Big Bang was originally proposed in the context of making all the elements. But the lack of a stable nucleus with atomic weight A=5 meant that only isotopes of hydrogen, helium and a trace of lithium are produced in Big Bang Nucleosynthesis. In the original Steady State proposal, all of the heavy elements were produced in stars by burning hydrogen into helium and then combining several helium nuclei [alpha particles] into heavier nuclei like carbon (3 alpha particles) and oxygen (4 alpha particles). In general the heavy element abundances relative to hydrogen are proportional to each other. Some stars have very little oxygen and these usually also have very little iron, and so on. But helium is definitely an exception to this rule. There is a non-zero floor to the helium abundance as the oxygen abundance goes to zero. This is shown in the plot at right which shows the helium and oxygen abundances relative to hydrogen by number of nuclei in the Sun and several ionized hydrogen nebulae [H II regions] in our Milky Way [M42 is the Orion nebula, M17 is the Omega nebula], in the nearby dwarf galaxies known as the Large and Small Magellanic clouds [LMC and SMC], and in other extragalactic H II regions.

This plot clearly shows that solid line, which allows for the primordial helium produced in the Big Bang, is a much better fit than the dashed line which is the prediction of the Steady State model with no primordial helium. The data for this plot were taken from Figure 1b of a recent paper on the element abundances in the Sun. Shortly before the discovery of the CMB killed the Steady State model, Hoyle & Tayler (1964, Nature, 203, 1008) wrote "The Mystery of the Cosmic Helium Abundance" in which they decided that most of the helium in the Universe was not produced in stars. Hoyle held open the possibility of explosions in supermassive objects instead of a single Big Bang, but ordinary stars were ruled out.

The page also mentions that although Hoyle abandoned the original steady-state model, he continued to advocate a "quasi-steady state cosmology" (QSSC) where the universe continually expands and contracts in an oscillatory way, and the author of the page gives some technical arguments as to why this model still can't adequately account for all the observations that are generally taken to support the Big Bang model.