Why is an improbable early universe unacceptable?

  • Context: Undergrad 
  • Thread starter Thread starter student34
  • Start date Start date
  • Tags Tags
    Early universe Universe
Click For Summary
SUMMARY

The discussion centers on the improbability of the early universe, particularly in relation to quantum fluctuations and the concept of the Boltzmann brain. Participants argue that while the universe's ordered state seems unlikely, it is not surprising given that it has already occurred. The anthropic principle is referenced to explain why observers exist in this universe, despite the low probability of its specific configuration. The debate highlights the challenges in cosmology regarding the measure problem and the implications of multiverse theories.

PREREQUISITES
  • Understanding of quantum fluctuations and their role in cosmology
  • Familiarity with the anthropic principle and its implications
  • Knowledge of the Boltzmann brain concept and its relevance to probability
  • Basic grasp of general relativity (GR) and phase space in cosmological models
NEXT STEPS
  • Research the implications of the anthropic principle in cosmology
  • Study the Boltzmann brain problem and its critiques
  • Explore the measure problem in cosmological theories, including eternal inflation
  • Investigate the role of quantum fluctuations in the early universe and their effects on cosmic evolution
USEFUL FOR

Cosmologists, physicists, and anyone interested in the foundational questions of universe formation and the implications of quantum mechanics on cosmological theories.

  • #31
houlahound said:
Please define what a measure problem is.

A measure problem is either when different measures applied to the same space in a theory produce different predictions or there is no way to define a measure on a space at all.

Measures in set theory and topology are ways to assign numbers to subsets. They generalise lengths, areas and volumes.

https://en.wikipedia.org/wiki/Measure_(mathematics)

Measures also apply to probability spaces so come into topics like entropy and quantum theory.

Measure problems are endemic in cosmological theories and many different regularisation procedures have been created to overcome them but none are generally accepted. In eternal inflation theories the problem is how to apply probability measures to infinite sets of causally disconnected universes. In canonical quantum gravity the Wheeler-deWitt equation is regularisation dependent.

https://en.wikipedia.org/wiki/Measure_problem_(cosmology)

houlahound said:
Please define what a measure problem is.
 
  • Like
Likes   Reactions: houlahound

Similar threads

Undergrad Why was the early universe's entropy low?
  • · Replies 1 ·
Replies
1
Views
2K
High School Low entropy early Universe and the heat death musings
  • · Replies 5 ·
Replies
5
Views
3K
Graduate Late Photons from the Early Universe?
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad 3 questions about a paper on density fluctuations in the Universe
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad How long would it take the Universe to generate an Earth-like chemistry?
  • · Replies 8 ·
Replies
8
Views
2K
  • Featured
Undergrad Early large galaxy studies
  • · Replies 10 ·
Replies
10
Views
5K
Undergrad Density fluctuations in a homogeneous linearly expanding universe?
  • · Replies 7 ·
Replies
7
Views
3K
High School Why is the low entropic state of the early universe a puzzle
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad Bubble universes and physical constants
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad New research puts age of the Universe at 26.7 billion years
  • · Replies 6 ·
Replies
6
Views
4K