December, 2014Archive for

Is Time Travel Possible?

Monday, December 29th, 2014

The ability to manipulate one’s place in time has often been embraced as a key plot element in science fiction. But how realistic is traveling forward or backward in time? The answer might surprise you.

Traveling back in Time

Artist rendition of a wormhole traversing a curved spacetime.

Unfortunately for Marty McFly and Doc Brown, traveling back in time is not as simple as strapping a flux capacitor onto a Delorean. In fact, there are a number of physics laws that prevent traveling against the arrow of time entirely. Theoretically, the only way one could travel to an earlier point in time would be to utilize a wormhole. A wormhole is a cosmic “shortcut” between two points in spacetime. Entering on one end would result in exiting the other end faster

than light could get to that point on it’s own, effectively getting to the destination before time does. Unfortunately, the likelihood of finding a stable wormhole capable of allowing anything to pass through it is almost zero, so traveling to the past may never be a possibility.

Traveling into the Future

This is where things get interesting. Scientifically, it is quite possible to time travel to the future. This is done utilizing Einstein’s Theory of Relativity, which allows for time to pass at different rates depending upon the environment the observers exist in. This concept is referred to as Time Dilation.

 

Photon clock on a rocket ship as viewed from the rocket and from an outside observer.

Relative Velocity Time Dilation

One postulate of the Theory of Special Relativity states that light will always travel at the same velocity in a vacuum, regardless of the velocity and direction of the source. While on the surface this doesn’t seem particularly interesting, it actually has unexpected consequences on the passage of time.

Imagine two mirrors facing each other, one meter apart. Now imagine a photon of light bouncing back and forth between those two mirrors. At rest, the photon will bounce off each mirror approximately three hundred million times per second, as this is the speed of light.

Now imagine that device on a rocket ship traveling close to the speed of light. Just like throwing a ball up and down on a train, to observer A on the rocket ship, the light looks like it’s bouncing up and down, just like it was at rest. However, to an observer B outside of the ship watching it rocket past, the path of the photon looks like it is traveling on an angled trajectory.

Because the observer B sees the photon travel at a non-vertical trajectory, it actually appears to travel slightly more than one meter between each mirror. But since light MUST always at the speed of light, that extra distance means it takes slightly longer to bounce between the mirrors, according to the observer B. Therefore, the clock looks to be moving at a slower rate than what the observer A sees, as it is bouncing at less than three hundred million times a second.

In essence, the time that passes “feels” the same to both observers, but the one on the rocket ship will actually experience a shorter duration of time relative to the outside observer. This phenomenon can then be used to manipulate time in such a way that a short period of time can pass for someone traveling at an extremely fast rate of speed relative to the Earth. For example, people on a rocket traveling at 87% the speed of light could travel for two year’s worth of Earth time, and only have aged one year.

Gravitational Time Dilation

The Theory of General Relativity adds the element of gravity to Einstein’s equations. In Newtonian Physics, gravity and acceleration are essentially analogous when it comes to calculations. Therefore, an observer close to a source of high gravity such as a black hole, will experience time travel at a slower rate relative to an observer further away from the gravitational source.

For instance, if you could shrink all of Jupiter’s mass down to a 5 meter wide sphere and stand next to it, time would travel four times slower for you than an observer in empty space.=

A Relativistic Tug of War

One interesting consequence of these two time dilation methodologies is their apparent cancellation in regards to Earth’s satellites. Satellites travel much more quickly around the planet than we do on the surface, which should slow their time relative to ours. However they also are further from Earth’s gravity, which means the surface’s time should be slower. So which wins out?

In fact, it depends upon the distance of the orbiting satellite. At around 3166 km above Earth’s surface, the effects of motion and gravitational time dilation cancels out. Below this distance, such as where the ISS orbits, the relative motion governs the time change. Further out, such as where GPS satellites exist, the difference in gravity is a more significant contributor to the time dilation. In fact, GPS satellites have to be programmed to account for this small but significant difference in time.

Past, Present, and Future – Current Events in Space

Monday, December 8th, 2014

2014 was a big year for space science and exploration, and 2015 is poised to be just as exciting. Lets take a look back at some of the year’s biggest stories from NASA, ESA, other government agencies, and the private space industry, and look forward to what is coming in 2015.

Rosetta’s orbit of 67P

Rosetta and Philae

Arguably the most widely covered space mission of the year was the European Space Agency’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko. The Rosetta spacecraft was launched in 2004 and arrived at the comet on August 6, 2014. Rosetta used four different slingshots around both Earth and Mars to build enough speed to catch up to 67P, which is traveling at about 84,000mph. In total, the spacecraft has traveled more than four billion miles in it’s ten year journey.

Philae Lander

On November 12, 2014, the lander portion of the Rosetta mission, known as Philae, landed on the surface of Comet 67P. Because the comet is relatively small (only about 2.5 miles in diameter), the gravity is not strong enough to hold objects to it. Philae was designed to use both harpoons in its feet, as well as a top-down thruster to hold it to the surface. Unfortunately, both devices failed, and Philae went skipping across the surface of the comet. This resulted in a landing location with little sunlight, rendering the craft unable to continue operating due to power shortages after about three days. 

Despite the landing troubles of Philae, the mission has been considered a monumental success, and significant scientific research is being accomplished because of the information Rosetta and Philae have gathered. Rosetta will continue to orbit Comet 67P until December 2015. During this time, the comet will make a closer approach to the Sun, which has the chance to increase the power received by Philae, to the point where it could be awoken again.

 

Orion Capsule and Delta IV Second Stage

Orion Exploration Flight Test

Another heavily covered space event occurred just a few days ago. The Orion spacecraft, NASA’s first spacecraft since Apollo designed to take humans beyond low Earth Orbit, was launched on it’s very first flight on December 5th. Orion was elevated to a distance of 3,600 miles above the Earth’s surface, and returned through the atmosphere at 20,000 miles an hour. This velocity was necessary to test Orion’s heat shield, which will protect astronauts on their return trip from deep space.

Orion was launched atop a United Launch Alliance Delta IV rocket. Orion is ultimately destined to ride atop the Space Launch System (SLS), which will be tested for the first time in 2018. Orion’s ultimate goal is to transport humans to and from Mars, which NASA has projected for a mid 2030 timeframe.

Boeing’s CST-100 (left) and SpaceX’s Dragon

 

Commercial Crew Transportation Program

In September of 2014 NASA announced partnerships with two companies, SpaceX and Boeing, for manned transportation to the International Space Station. Since the end of the Shuttle program in 2011, NASA has been contracting rides to the ISS for its astronauts on the Russian Soyuz spacecraft. in 2017, the United States will return to the business of human space travel with the Boeing CST-100 and SpaceX Dragon spacecraft.

 

New Horizons Spacecraft

New Horizons

NASA’s New Horizons mission is currently en route to Pluto. Launched in 2006, New Horizons plans on being the first spacecraft to visit the solar system’s former ninth planet. This will give us the best pictures ever of Pluto and it’s moon, Charon. New Horizons just woke up from it’s most recent slumber, and plans on arriving at Pluto On July 14, 2015. Because of the velocity needed to get to Pluto’s orbit, New Horizons will not stop at Pluto, but instead perform a flyby on it’s way into the Kuiper belt, to study other Trans-Neptunian objects.

 

Dawn Spacecraft

Dawn

Dawn is an unmanned spacecraft currently approaching Ceres, the only dwarf planet in the inner solar system, and just over one third the diameter of our Moon. Dawn was launched in September 2007, and is set to arrive in orbit around Ceres in April 2015. In 2011 Dawn also visited Vesta, a large asteroid in the asteroid belt, and will become the first spacecraft to orbit two different celestial bodies. Dawn uses a unique and experimental Ion Thruster propulsion system to allow it to enter and exit orbits efficiently. It is one of the first missions to utilize this technology, which accelerates charged particles with electromagnetic fields.