Relativity-5: Galilean and Einsteinian relativity

(For previous posts in this series, see here.)

In the previous post in this series, I posed the situation where, seated in my office, I observe two events on the sidewalk outside my window and measure the locations and time of two events and deduce the distance between them and the time interval according to the rules for using my own ruler and watch. Now suppose another person is moving with respect to me (say in a train that passes right by where the two events occur) and sees the same two events as I do and measures the locations and times of the two events and deduces the distance and time interval between them using her ruler and watch. Will her measurements agree with mine?

When it comes to location and distance measurements, it is not hard to see that the two results will be different. When I take ruler readings of the two events, the ruler is not moving compared to the two events. But because the person in the moving train’s ruler will be moving along with her in the train, the ruler readings of where the two events occurred will be affected by her motion. After the person in the train takes the reading on her ruler at the location where event A occurred, by the time the later event B occurs, she and her ruler would have moved along with her train and so the ruler reading for event B would be different from what would have been obtained if the ruler had been stationary. So the locations and the measured distance between the two events based on her two ruler readings will be different from those based on my two ruler readings.

What about the time interval between events A and B? It used to be thought that even though the two observers used different clocks and they were moving relative to each other, as long as the clocks were identical and synchronized properly, the two observers would at least agree on this because it seemed so commonsensical that time was some sort of universal property, independent of the observer measuring them or her state of motion. Time measurements were said to be invariants.

These relationships between the location and time measurements made by observers moving with respect to one another were first postulated by Galileo. It is now known as ‘Galilean relativity’. Galileo used these relations to show why, even though the Earth was moving quite fast through space (a seemingly absurd idea at that time), a ball thrown vertically upwards would fall back down to the same point from where it was thrown, and not be displaced because the Earth had moved during the time that elapsed. This everyday observation had previously been used to argue that the Earth must be stationary but Galileo turned it around to show that it was consistent with the Earth moving.

But one consequence of the assumption that time is an invariant is that if you measure the speed of light (by taking two events, one consisting of light being emitted at one point and the other of it being detected at another point and dividing the difference in ruler readings between the two events by the time interval between the events), you would get different values for two observers in relative motion to each other, since the distances traveled (i.e., the differences in the ruler readings) would be different for the two observers but the time interval would be the same. In other words, the measured speed of light was not an invariant but depended on the speed with which the observer was moving.

What Einstein postulated (based on several reasons that I will not get into here) was that the speed of light was the same for all observers. In other words, it is the measured speed of light that is an invariant, the same for all observers irrespective of how they are moving. One important consequence of this is that the elapsed time between two events is no longer an invariant, and depends on the observer. Time is no longer a universal property but depends on who is measuring it. The difference in measured times is tiny for the normal speeds we encounter in everyday life, which is why we don’t perceive it. But it does leads to things like the celebrated ‘twin paradox’ where if you have a pair of identical twins, one remaining on Earth and the other going in a rocket at high speed to a distant star and returning, the traveling twin would have aged much less than the one who stayed home.

Needless to say, this caused some consternation and it took some time for people to be persuaded that this seemingly bizarre result was correct. What Einstein did was force us to be more precise about how we measure the location and time at which events occur, so that we can meaningfully compare the results of different observers viewing the same events.

Next: Measuring time and space more precisely.

Herman Cain’s 9-9-9 tax plan

Herman Cain has been getting a lot of mileage about his ‘simple’ 9-9-9 tax plan. Jared Bernstein says that it will result in a big tax increase on the middle class and a huge tax cut for the very wealthy. I have seen similar conclusions reached by other analysts.

While this is a goal of the oligarchy, they would like to achieve their goal in more subtle ways. The very transparency of Cain’s scheme is likely to be the thing that pricks his bubble and sends him back into the ranks of the stragglers for the Republican nomination.

How to choose passwords

All of us who are heavy users of computers and the internet know that we get drowned in the number of passwords we need and that it is hard to keep track of them.

James Fallows describes what he learned after his wife’s Gmail account was hacked and gives a list of suggestions for passwords.

The science, psychology, and sociology of creating strong passwords is a surprisingly well-chronicled and fascinating field. On The Atlantic‘s Web site, we will describe some of the main strategies and the reasoning behind them. Even security professionals recognize the contradiction: the stronger the password, the less likely you are to remember it. Thus the Post-it notes with passwords, on monitor screens or in desk drawers.

But there is a middle ground, of passwords strong enough to create problems for hackers and still simple enough to be manageable. There are more details on our site, but strategies include:

  • Choose a long, familiar-to-you sequence of ordinary words, with spaces between them as in an ordinary sentence, which more and more sites now allow. “Lake Winnebago is deep and chilly,” for instance. Or “my favorite packer is not brett favre.” You could remember a phrase like that, but a hacker’s computer, which couldn’t tell spaces from characters, would see only one forbiddingly long password sequence.
  • Choose a shorter sequence of words that are not “real” English words. I once lived in a Ghanaian village called Assin Fosu. I can remember its name easily, but it would be hard to guess. Even harder if I added numbers or characters.
  • Choose a truly obscure, gibberish password—”V*!amYEg5M5!3R” is one I generated just now with the LastPass system, and you’re welcome to it—and then find a way to store it. Having it written down in your wallet is one, though the paper it’s on shouldn’t say “Passwords” at the top. The approach I prefer, and use for some passwords, is to entrust them to online managers like LastPass or RoboForm. Even if their corporate sites were hacked, that wouldn’t reveal all your passwords, since the programs work by storing part of the encoding information in the cloud and part on your own machine.

At a minimum, any step up from “password,” “123456,” or your own birthday is worthwhile.

Finally, use different passwords. Not hundreds of different ones, for the hundreds of different places that require logins of some kind. The guide should be: any site that matters needs its own password—one you don’t currently use for any other site, and that you have never used anywhere else.

“Using an important password anywhere else is just like mailing your house key to anyone who might be making a delivery,” Michael Jones of Google said. “If you use your password in two places, it is not a valid password.”

I asked my experts how many passwords they personally used. The highest I heard was “about a dozen.” The lowest was four, and the norm was five or six. They all stressed that they managed their passwords and sites in different categories. In my own case, there are five sites whose security really matters to me: my main e‑mail account, two credit-card sites, a banking account, and an investment firm. Each has its own, good password, never used anywhere else. Next are the sites I’d just as soon not have compromised: airline-mileage accounts, Amazon and Barnes & Noble, various message boards and memberships. I have two or three semi-strong passwords I use among all of them. If you hacked one of them you might hack the others, but I don’t really care. Then there is everything else, the thicket of annoying little logins we all deal with. I have one or two passwords for them too. By making it easy to deal with unimportant accounts, I can concentrate on protecting the ones that matter.

Seems like good advice.

Dogs Decoded

The PBS series Nova has a wonderful program about dogs with the above title that looks at the amazing things we are learning about them. It was broadcast on October 12 and will be available for free viewing online for only a week after that. Don’t miss it, especially if you are fond of dogs.

I particularly enjoyed it because there were lots of scenes in which they showed dogs that were exactly like Baxter, the Wonder Dog.

baxter.jpg

Five signs that Americans are moving away from religion

Tana Ganeva points to various data that support this idea.

  1. American religious belief is becoming more fractured.
  2. Non-belief — and acceptance of non-belief — on the rise
  3. Growing numbers of young people who do not identify as religious
  4. Hate group that exploited religion to bash gays hemorrhaging funds
  5. Getting married by friends

What the last item refers to is that more and more people are not getting married with the trappings of religion, choosing instead more informal, secular wedding ceremonies.

To vote or not to vote

Recently at a dinner someone made a comment that one hears often, that those who do not vote in elections have no right to then complain about the government’s actions or the way society is run. The speaker was implying that voting is the admission price one pays for the privilege of entering the public debate.

I disagree with this sentiment, for many reasons. For one thing, one can have principled non-voting. If one thinks the system is rigged, and that elections are merely a façade designed to give legitimacy to a corrupt political system, then not voting can be a very principled and political act. In such cases, not voting is akin to a boycott, or voting with one’s feet. There is a reason that almost all totalitarian societies still feel obliged to hold fraudulent elections in which the ruler gets an overwhelming majority, because elections tend to confer at least some legitimacy on the winner, even if it is rigged, as long as participation is reasonably high. This is why in many autocratic countries people are forced to vote or the ballot boxes are stuffed with counterfeits, while opponents of the regime urge people to boycott them.
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Bipartisanship in the service of the oligarchy

If you were paying close attention, you may have noticed that yesterday Congress, which is supposed to be locked in partisan gridlock that has paralyzed it, managed in a bipartisan manner to pass quite easily and with little fanfare major free-trade agreements with Panama, Colombia, and South Korea. The House passed the South Korea agreement by a vote of 278 to 151, Panama by 300 to 129 and Colombia by 262-167. In the Senate, the South Korean plan passed by a vote of 83 to 15, Panama by 77 to 22 and Colombia by 66 to 33.

Whether one thinks such agreements are good for everyone or not, the oligarchy definitely favors them because anything that enables them to move goods, money, and manufacturing capacity more easily and cheaply across borders enables them to make more money.

These agreements had been negotiated by George W. Bush but had stalled in Congress because of opposition from the labor movement that they would cost jobs here. This time they passed easily, thanks to the support of president Obama, which illustrates once again that the oligarchy can sometimes get more of what it wants under a Democratic administration than under a Republican one. It also illustrates once again how noisy partisan gridlock only comes into play when it comes to doing things that benefit ordinary people, and miraculously melts away when the oligarchy’s interests are involved.