Time travel remains a fixture of science fiction
Time travel is a tried and true science fiction staple. It usually involves being able to fly in a spaceship faster than the speed of light or diving through a wormhole. None of those technologies currently exists in the real world of science.
Astrophysicists often discuss wormholes: Can
one be created without a black hole as the door; would it be stable; would it be large enough to travel through without getting destroyed in the process; and what kind of energy source might it take to create one? So far, no one has any idea how to do any of that. NASA currently is testing an engine, known as the EM Drive, which seems to have potential for faster than light travel. But, as of now, no one even knows how it generates thrust.
Albert Einstein said that no object with mass, like a spaceship, can go at the speed light as it would take an infinite amount of energy to get there. He didn’t exactly say nothing could travel faster than the speed of light. You might think that if it can’t travel AT the speed of light, how can a spaceship go faster than the speed of light? Physics allows for a phenomenon called “tunneling” where an object can be in condition A and B but not in between. Physicists run rather simple experiments where objects go from A to B even though they can’t be in between the two states. So far, they’ve only done such experiments with objects like electrons, not spaceships, but that may just be a matter of technology.
Scientists also have discussed ways to create wormholes without a black hole doorway. It only takes a lot of energy. Like a sun’s worth of energy, but still not impossible, in theory.
But here is the rub with time travel. One of the most fundamental truths physicists know about the universe is the conservation of energy. Since Einstein showed us that matter and energy are intimately related via his famous equation E=mc², the full conservation rule is that the total amount of mass and energy must be conserved. It’s known as the First Law of Thermodynamics.
Let’s say I want to travel back in time to meet George Washington. Once I left this time, there is suddenly less mass-energy in the universe now and there is suddenly more massenergy in the universe in 1776. It all averages out, but the First Law of Thermodynamics is exact, not an average. This appears to make time travel impossible — unless, somehow, the exact same amount of mass-energy transfers from then to now at exactly the same instant. But you might randomly take half a person from then and move him or her to now.
I think I’d just leave it alone.
Also ...
July highlights: Earth’s orbit around the sun isn’t perfectly circular. It’s oval in shape, so that at some date we are closest to the sun and six months later we are farthest from the sun. On Friday, we will be at aphelion, the farthest point from the sun. The sun’s center will be 94,508,365 miles from the center of Earth. Perihelion, when we are closest to the sun, occurred back on January 3, when the Earth and the sun were 91,402,705 miles apart.
I know, it’s counterintuitive that we’d be closer to the sun when it’s cold and farthest from the sun when it’s hot. But it’s just the reverse for the southern hemisphere.
A partial solar eclipse occurs on the July 12 with an associated total lunar eclipse following on the July 27. To see either, you’ll need to travel to the Southern hemisphere. We’ll get none of either in Oklahoma.
Planet visibility report:
For the first three weeks of July, both Venus and Mercury grace the western horizon after sunset. Mercury is never very far from the sun, so your best bet to see it is from a location with an unobstructed view of the horizon. Venus is higher and brighter and you should have no trouble spotting it. Jupiter and Saturn are also up at sunset, but much farther west. Mars rises around 11 p.m. early in the month and hits the eastern horizon around 9 p.m. at month’s end. At chart time, 10 p.m. on July 15, four of the five visible planets are up: Venus, Jupiter, Saturn and Mars. New moon occurs on the July 12 with the partial solar eclipse and full moon comes on the July 27 with the lunar eclipse.
Wayne Harris-Wyrick is an Oklahoma astronomer and former director of the Kirkpatrick Planetarium at Science Museum Oklahoma. Questions or comments may be emailed to wizardwayne@ zoho.com.