# Lecture 001

1. explain galexy motion more "complex" than explain development of income inequality or not? In the context of physical scientists trying to predict galaxy motion by introducing a new concept of dark matter in particle physics and social scientists trying to develop a theory for the development of income inequality, I think the phenomena about development of income inequality is more complex than the phenomena about galaxy motion. In my opinion, if a phenomenon, reduced to its raw data form, has more data points in the data set that can't be captured by its corresponding theory, then the phenomenon is more complex (and vice versa). In the article "Why Hasn’t Democracy Slowed Rising Inequality? (Excerpts)", the author mentions the correlation between political polarization with the income share of the top 1 exceeds 0.9. In another word, there are more than R^2=81% of data points can be explained by the theory. However, from common sense, in order for a Hadron collider (a technique mentioned in "Is Dark Matter Real?") to announce the detection of a new particle of dark matter, the probability of null hypothesis should reach as low as 5 sigma (or 3x10^-7). In another word, there is less than 0.00003% chance that the null hypothesis is true. This indicates that a theory about galaxy motion is less likely to be false-positive than a theory about development of income inequality. This is the same thing as saying a theory about development of income inequality is less able to explain the full data set, making its corresponding phenomena more complex by my definition of complexity.

First Draft That Can't Be Used Because the Articles Don't Provide Enough Information: In my opinion, the complexity of a phenomena is the complexity of the simplest theory we have that can explain such phenomena. The complexity of a theory is the product of the complexity of their assumptions, while the complexity of the assumptions can be measured by the number of bits needed to accurately depict the assumption using certain language. (For simplicity, think of it as the number of characters, including symbols, in English that can accurately explain an assumption.) Therefore the complexity of a phenomena can be measured by the number of English characters in the assumptions needed to explain the simplest theory to the phenomena.

1. Is dark matter a ad hoc(adjusting) hypothesis? (what part of reading suggest is and is not)

2. The reading suggest that dark matter is a ad hoc hypothesis because the reading points out that the hypothesis is "too flexible" because experiment can tweak the amount of dark matter exists in galaxies to fit observational data however they wanted. Therefore the hypothesis is not simple enough to safely pass the Occam's razor test.

3. In my opinion, if ad hoc has negative association, then it shouldn't be. A hypothesis can still be the simplest if it is deducted by adding element to the original theory.

4. are two claim "laws of nature" ? (democracy prevents the development of income inequality, all matter attracts all other matter with force proportional to the inverse square of their distance from one another)

5. Claim is a claim, it can't be the true. Therefore none of them can be considered laws of nature even with sufficient support. A law of nature, by my definition should have the following properties: 1. it can't be violated by observed data. 2. it can't be violated by future data. Since we, as human, only can use statistics as tool for observe things that happened in the past, we can't say for sure one theory is the law of nature.

6. voting percentages by income bracket cause income inequality? how might people challenge this?

7. correlation can't imply causation

8. any seemingly correct argument can be made (for example: saying that assumption about equal voting opportunity is false)

9. challenge: voting percentages by income bracket might have confounding variables.

10. good argument complete assumptions: e.g. data show the poor vote for people who would actually benefit them. data show the poor aren't controlled by the media.

11. Similarity / Differences between two potential causal factor?

12. Similarity: they are all within-a-range reasonable potential causal factor. Because those factors, by our prior knowledge, more likely to have causal relationship with the phenomenon we observe because connecting the factor with the phenomenon requires less additional (simpler) theory (I say simpler here because we can use previously known theory as a part of our new theory. That is good because these kind of theories are usually self-consistent)

13. Differences: 1. dark matter use continuous variable where as social science use categorical (often by human choice) variable that is more subjective. 2. for natural science, we often assume laws are consistent in space-time, but theories may vary by space-time in social science.

### Is Dark Matter Real?

Problem: stars move too quickly at the center of Galaxy Solution

1. modify gravity perimeter in some case

2. not completely align with Einstein's general theory of relativity

3. inelegant

4. can't explain galaxy cluster

5. introduce dark matter

6. Large Underground Xenon (LUX) and other Hadron collider turns negative

7. abnormal strong correlation between dark matter and normal matter (resulting later paragraph about low surface brightness galaxies)

• fine tune: dimmer the system, more dark matter
• "stellar feedback": supernovae can't blow dark matter away
8. predict fewer dwarf galaxies than observed

9. failed to predict galaxies and their satellite galaxies align along a single plane

10. can account for background radiation

### Why Hasn't Democracy Slowed Rising Inequality

Assumption: voters can vote for after-tax to transfer equality when there is unbalance Observation:

• republicans are winning

• polarization happening between two party

• republicans is becoming more conservative, while democrats stays

• polarization positively correlated to inequality (0.9 correlation for the last 10 years, and correlate exist in the past 100 years)

Propose: polarization and free-market cause low support for policies that has to do with inequality

Observation:

• more poors are noncitizens

• poor citizens don't vote as much as rich

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