Tuesday, June 27, 2017

Black Strings


One of the longest outstanding mysteries in physics is how gravity is related to the other fundamental forces, such as electromagnetism. One theory, first proposed in 1919, showed that if an extra dimension is added to the universe, gravity still exists in the first four dimensions (three space dimensions and time), but the way this four dimensional space curves over the extra fifth dimension, naturally produces the other fundamental forces. However, we cannot see or detect this fifth dimension, so it was proposed that the extra dimension was curled up, and hence became invisible to us. This theory was what ultimately led to string theory, and is still included at the heart of most string theory analysis.

Since this extra dimension is so small, only tiny objects, such as particles, can move along it. In these cases, they ultimately just end up where they started, since the extra dimension is curled up on itself. However, one object that becomes much more complex in five dimensions is a black hole. When extended to five dimensions, it becomes a “black string,” and unlike a normal 4D black hole, it is unstable (this ignores the fact that 4D black holes eventually evaporate). This black string will destabilize into a whole string of black holes, connected by further black strings, until the black strings are pinched off entirely and leave the set of black holes. These multiple 4D black holes then combine into one larger black hole. The most interesting thing about this is that, using current models, the final black hole is a “naked” singularity. That is, it has no event horizon surrounding it. This violates the Cosmic Censorship Hypothesis, which says that all singularities must be surrounded by an event horizon, in order to avoid the time-travel effects that are believed to happen near a singularity from changing the history of the entire universe, as they can never escape from behind an event horizon.

Sunday, June 25, 2017

Protagoras


Man is the measure of all things.

This is the most famous saying of Protagoras, though it is in fact, only the first portion of his statement. The full line runs ‘Man is the measure of all things; of things that are that they are, and of things that are not that they are not.’ Protagoras’ relativism is one of the most extreme ever argued. This means that truth is relative and for each individual truth is different. This can be true with things like temperature – you might find the evening chilly, but for me it is warm. However, we can all agree on the absolute temperature in degrees. Protagoras would disagree and would say that all of our knowledge is sense based and therefore unique to each individual. The problem with relativism is that it makes philosophical discussion impossible; what you think you say and what I hear might be completely different, if we are unable to agree on objective truth.

Protagoras of Abdera was one of several fifth century Greek thinkers (including also Gorgias, Hippias, and Prodicus) collectively known as the Older Sophists, a group of traveling teachers or intellectuals who were experts in rhetoric (the science of oratory) and related subjects. Protagoras is known primarily for three claims (1) that man is the measure of all things (which is often interpreted as a sort of radical relativism) (2) that he could make the "worse (or weaker) argument appear the better (or stronger)" and (3) that one could not tell if the gods existed or not. While some ancient sources claim that these positions led to his having been tried for impiety in Athens and his books burned, these stories may well have been later legends. Protagoras' notion that judgments and knowledge are in some way relative to the person judging or knowing has been very influential, and is still widely discussed in contemporary philosophy. Protagoras’ influence on the history of philosophy has been significant. Historically, it was in response to Protagoras and his fellow sophists that Plato began the search for transcendent forms or knowledge which could somehow anchor moral judgment. Along with the other Older Sophists and Socrates, Protagoras was part of a shift in philosophical focus from the earlier Presocratic tradition of natural philosophy to an interest in human philosophy. He emphasized how human subjectivity determines the way we understand, or even construct, our world, a position which is still an essential part of the modern philosophic tradition.

Saturday, June 24, 2017