The good news is that physicists have developed complete, tested and verified models of time travel that perfectly explain how objects (including humans!) can, and do, travel through time.
The bad news is that it’s the ultimate one-way street. We constantly are traveling through time, but our velocity in that direction is, with all the unfortunate consequences, unstoppable.
The theories of special and general relativity fully explain the rich physics of how to manipulate the rate at which clocks can tick due to large relative velocities and/or different altitudes — not to mention the even more significant effects of strong gravitational fields or near-light speed travel. It’s unavoidable to draw the analogy between these models and humans’ perception of how quickly time seems to pass; an hour in lecture can seem like a minute or a day depending on your frame of mind.
Understanding time travel, at least in this sense, is more than an academic exercise. The observable consequences of relativity are relevant in many of the processes that we take for granted. For instance, not a day goes by that I don’t rely on my GPS to tell me how long it will take for me to get home. This technology would be useless without a careful understanding of why the clocks on the GPS satellites tick at a (relative) different rate to those we have in our phones.
The great mystery, however, is not the fact that we travel through time in one direction, but rather why we travel in one direction. Macroscopic physics — thermodynamics, to be exact — dictates the rules that compel us forward, and forbid us to travel backwards, through time. On the other hand, microscopic physics has (almost) nothing to say about the choice of early versus late or young versus old. All microscopic laws of physics are time-reversal symmetric, meaning that these laws don’t care if time goes forward or backward. The origin of the arrow of time, the principle that dictates that we bleed after we’re cut, is an open question in physics.
In short, we’re great at time travel; we know a lot about how time works and have harnessed its power in multiple ways. The limitations of this model that get us down, but these same limitations help our GPS get us to where we need to go.
A: JAY CORRIGAN | PROFESSOR OF ECONOMICS
Slices of the economic pie are more lopsided than ever before. According to recent data, the richest 10 percent of American households earn just more than half of all U.S. income. That’s the highest fraction since the federal government started keeping these sorts of records 100 years ago. And the U.S. isn’t the only place where the gap between rich and poor is growing. During the last 40 years, the richest 10 percent gained ground in Canada, Germany and Japan.
So what explains this increase in income inequality across rich countries? Economists most often point to technological changes that have made the most talented workers ever more productive. As an example, consider that the only way to listen to professional musicians at the turn of the 20th century was to go to a live performance. The most talented performers played in the largest venues and, therefore, made more money than their less-talented peers, but the difference would have been relatively modest.
Today, most of us listen to recorded music. And because an iTunes download costs the same whether it’s recorded by the top artist in a genre or by someone less popular, the most-talented performers now capture a much larger share of our entertainment dollars. Thousands of musicians still are scratching out a living, but technology has increased the gap between the most-talented and the slightly less-talented. Something similar has happened in most industries.
To understand what, if anything, can be done to reduce income inequality, it helps to look back to the 1940s, ’50s and ’60s, when income inequality actually decreased. That's because the supply of highly skilled workers increased more rapidly than the demand for their services, keeping their incomes — and income inequality — in check. This increase in supply was due to an increase in college graduates and women entering the workforce. Unfortunately, both of those trends have leveled off since about 1980.
If there’s one area where there’s still low-hanging fruit, it’s immigration. Immigrants create about half of all successful startups, but we make it hard for highly skilled immigrants to live and work in the U.S. Increasing the cap on the number of visas issued to highly skilled immigrants each year — or removing the cap entirely — would increase the supply of top talent, reducing income inequality.