All articles in the Physics category

Abrupt climate change

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Posted July 19th, 2009 in Physics. Tags: , , , , , , .

One part of a recent survey caught my attention:

The strongest correlate of opinion on climate change is partisan affiliation. Two-thirds of Republicans (67%) say either that the Earth is getting warmer mostly because of natural changes in the atmosphere (43%) or that there is no solid evidence the Earth is getting warmer (24%). By contrast, most Democrats (64%) say the Earth is getting warmer mostly because of human activity. … The divide is even larger when party and ideology are both taken into consideration. Just 21% of conservative Republicans say the Earth is warming due to human activity, compared with nearly three-quarters (74%) of liberal Democrats. [Pew Research Center] (Skip to videos, data, index.)

In other words, most of the general public appears to believe that the existence of abrupt climate change A large-scale change in the climate system that takes place over a few decades or less, persists (or is anticipated to persist) for at least a few decades, and causes substantial disruptions in human and natural systems. (formerly known as anthropogenic ‘Human-caused’ global warming) is a question of politics rather than science. (more…)

Any FTL signal can be sent back in time

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Posted October 27th, 2008 in Relativity 2. Tags: , , , .

One surprising consequence of Einstein’s special theory of relativity is that any signal traveling faster-than-light (FTL) can be used to send a message to the past. Special relativity divides the entire universe into three distinct regions as seen by any observer: (more…)

Climate destabilization

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Posted April 7th, 2012 in Physics. Tags: , , , , , , .

The overwhelming majority of scientists endorse this statement:

“Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.” [IPCC Summary for Policymakers, 2007]

Here, “most” means at least 50% of the 0.55°C rise since 1950. Some mistakenly call this an “alarmist exaggeration” but it actually understates the human contribution because it’s easy to incorrectly conclude that the other 50% of the trend might be caused by natural forcing variations: (more…)

Fundamental flaws in general physics education

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Posted October 21st, 2008 in Physics. Tags: , , , , .

After years of serving as a physics teaching assistant at several public American universities, I’ve come to an alarming conclusion: students in today’s general physics courses (i.e. courses that don’t require calculus, intended for non-physicists) aren’t being taught physics. They might be learning how to mechanically calculate answers, but they’re learning very little about the actual scientific process of inquiring about the nature of reality. They aren’t learning how these physical laws were deduced in the first place– which is far more important than the intricate details of those laws. I think this educational deficiency contributes to widespread misconceptions such as the belief that the Earth’s seasons are caused by variations in the distance from the Sun, and the curious notion that toilets flush in opposite directions on different sides of the equator. (more…)

Outlive the stars

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Posted July 22nd, 2012 in Relativity 3. Tags: , , , .

Reythia asked me to write something uplifting, so I copied a recent conversation about general relativity and hypothetical sources of energy. (more…)

Quantum entanglement and parallel universes

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Posted October 23rd, 2008 in Quantum 2. Tags: , , , .

In 2007 I noticed a confusing post on Slashdot quoting from an article claiming that the no cloning theorem prevented entangled particles from being used for faster-than-light (FTL) communication. I had never heard of any FTL implications of the no cloning theorem, so I responded to this post to see if a less-dumb scientist could explain this connection to me (incidentally, I’m still waiting- someone please educate me!).

While the resulting conversation didn’t shed any light on the purported FTL implications of the no cloning theorem, DrVomact asked a question that eventually led to an enjoyable discussion (edited for clarity) about quantum entanglement and parallel universes. (more…)

Quantum teleportation

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Posted October 28th, 2008 in Quantum 3. Tags: , , , .

Teleportation, a term originally coined by science fiction, refers to a hypothetical technology that can transport objects (or, eventually, people) nearly instantaneously from one location to another without sending the object through the intervening space. Classically, one might approach this problem by attempting to record the states of all the particles constituting the object to be teleported; that information could then be transmitted to a distant receiver and used to reconstitute the object out of raw materials available at the receiver. For many years this approach to teleportation was considered implausible because of quantum mechanical concerns. For instance, a teleportation device must somehow record the precise positions and momenta of all atoms in an object in order to reconstruct the object on the other side. This simultaneous measurement of non-commuting observables is forbidden by the uncertainty principle. A more fundamental problem exists, though, which is evident even in situations where the uncertainty principle is not directly applicable. To illustrate this point, consider the teleportation of a (more…)

The faint young Sun paradox

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Posted May 24th, 2009 in Physics. Tags: , , , .

According to the standard solar model, the Sun’s brightness steadily increases because helium ash slowly builds up in its core. The introduction of heavier elements like helium forces the Sun to fuse hydrogen faster in order to prevent gravitational collapse, so it shines brighter as it ages. The Sun was ~25% dimmer 4 billion years ago compared to now.

Liquid oceans had already formed 4 billion years ago, so Earth’s temperature must have been above the freezing point of water. A faint young Sun presents a paradox: how could a 25% dimmer Sun warm the Earth enough to develop liquid oceans? (more…)

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