Question

 

1a. What is the anthropic principle and how does it relate to multiverse theories. Can such theories be tested? Why or why not?

1b. What is dark matter, and what evidence do astronomers have that it is an important part of galaxies and the universe? What is dark energy and what evidence do astronomers have that it is an important component of the universe?

1c. Why was the discovery of the cosmic microwave background important? What is the temperature of the observed CMB? What do astronomers think the small fluctuations in the CMB led to?

Answer 1

1a)

The anthropic principle is the philosophical premise that any data we collect about the universe is filtered by the fact that, in order for it to be observable at all, the universe must have been compatible with the emergence of conscious and sapient life that observes it. In other words, scientific observation of the universe would not even be possible if the laws of the universe had been incompatible with the development of sentient life. Proponents of the anthropic principle argue that it explains why this universe has the age and the fundamental physical constants necessary to accommodate conscious life, since if either had been different, we would not be around to make observations in the first place. As a result, outside the narrow range thought to be compatible with life it would seem impossible that life could develop.

There are two different formulations of the anthropic principle. The strong anthropic principle (SAP), as defended by John D. Barrow and Frank Tipler, states that this is all the case because the universe is in some sense compelled to eventually have conscious and sapient life emerge within it. Some critics of the SAP argue in favor of a weak anthropic principle (WAP) similar to the one defined by Brandon Carter, which states that the universe's ostensible fine tuning is the result of selection bias (specifically survivorship bias), therefore only in a universe capable of eventually supporting life will there be living beings capable of observing and reflecting on the matter

From science fiction to science fact, there is a concept that suggests that there could be other universes besides our own, where all the choices you made in this life played out in alternate realities. The concept is known as a "parallel universe," and is a facet of the astronomical theory of the multivers

The universe appears to be fine-tuned for human life, which leads some to conclude that the universe must have been created for us. The Anthropic Principle is an attempt to dispel that argument, by stating that humans could only exist in a fine-tuned world and thus that it is not surprising that our world is (and seems to be) fine-tuned. I argue that to dispel the most surprising fine-tuning coincidences–those regarding the physical makeup of the universe–the Anthropic Principle requires that there be multiple universes, each with different physical characteristics. I further argue that some modern scientific hypotheses relating to quantum mechanics and cosmology, if true, provide evidence for a multiverse with differing universes, which would allow the denial of the fine-tuning argument with the Anthropic Principle

For a start, how is the existence of the other universes to be tested? To be sure, all cosmologists accept that there are some regions of the universe that lie beyond the reach of our telescopes, but somewhere on the slippery slope between that and the idea that there is an infinite number of universes, credibility reaches a limit. As one slips down that slope, more and more must be accepted on faith, and less and less is open to scientific verification. Extreme multiverse explanations are therefore reminiscent of theological discussions. Indeed, invoking an infinity of unseen universes to explain the unusual features of the one we do see is just as ad hoc as invoking an unseen Creator. The multiverse theory may be dressed up in scientific language, but in essence it requires the same leap of faith.

1b)

Dark matter is a form of matter thought to account for approximately 85% of the matter in the universe and about a quarter of its total mass–energy density or about 2.241×10⁻²⁷ kg/m³. Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts think that dark matter is abundant in the universe and that it has had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with the electromagnetic field, which means it doesn't absorb, reflect or emit electromagnetic radiation, and is therefore difficult to detect.

Primary evidence for dark matter comes from calculations showing that many galaxies would fly apart, or that they would not have formed or would not move as they do, if they did not contain a large amount of unseen matter. Other lines of evidence include observations in gravitational lensing and in the cosmic microwave background, along with astronomical observations of the observable universe's current structure, the formation and evolution of galaxies, mass location during galactic collisions, and the motion of galaxies within galaxy clusters. In the standard Lambda-CDM model of cosmology, the total mass–energy of the universe contains 5% ordinary matter and energy, 27% dark matter and 68% of a form of energy known as dark energy. Thus, dark matter constitutes 85%^[a] of total mass, while dark energy plus dark matter constitute 95% of total mass–energy content.

Because dark matter has not yet been observed directly, if it exists, it must barely interact with ordinary baryonic matter and radiation, except through gravity. Most dark matter is thought to be non-baryonic in nature; it may be composed of some as-yet undiscovered subatomic particles. The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, in particular, weakly interacting massive particles (WIMPs). Many experiments to directly detect and study dark matter particles are being actively undertaken, but none have yet succeeded. Dark matter is classified as "cold", "warm", or "hot" according to its velocity (more precisely, its free streaming length). Current models favor a cold dark matter scenario, in which structures emerge by gradual accumulation of particles.

Although the existence of dark matter is generally accepted by the scientific community, some astrophysicists, intrigued by certain observations which do not fit some dark matter theories, argue for various modifications of the standard laws of general relativity, such as modified Newtonian dynamics, tensor–vector–scalar gravity, or entropic gravity. These models attempt to account for all observations without invoking supplemental non-baryonic matter.

1c)

Their detection of the Cosmic Microwave Background (CMB), the radiation left over from the birth of the universe, provided the strongest possible evidence that the universe expanded from an initial violent explosion, known as The Big Bang.

The anisotropy of the cosmic microwave background (CMB) consists of the small temperature fluctuations in the blackbody radiation left over from the Big Bang. The average temperature of this radiation is 2.725 K as measured by the FIRAS instrument on the COBE satellite

The cosmic microwave background is the afterglow radiation left over from the hot Big Bang. Its temperature is extremely uniform all over the sky. However, tiny temperature variations or fluctuations (at the part per million level) can offer great insight into the origin, evolution, and content of the universe.