Paradoxes of Time Travel

While time travel can sound fun and even plausible, we might run into some serious problems. These problems stem not from equations not being satisfied, but logic being broken. In this blog post, I am going to discuss three different types of paradoxes associating with traveling back in time as well as solutions to try and resolve these issues.

The first of these paradoxes is the bootstrap paradox, a paradox that is related to original information. This paradox does not necessarily change the course of history, but it does blur out the origin of the object in question. Let’s say I was to go into the future to learn about a single equation that can explain every phenomenon in the Universe and then told someone about it after I returned from my trip. That person may end up writing a book that contains information about that equation, which is why the future knows about that equation. In the end, we end questioning who and when this equation was made. 

Continuing on with paradoxes, the predestination paradox discusses the implications of changing an event in the past because of something that happened in the present. A classic example is of a man going back in time to save his girlfriend from a car accident. As he is in the past driving quickly to the eventual accident location, he hits his girlfriend, and kills her. He caused the death that made him travel back to the past in the first place.

The last paradox we are going to observe is the grandfather paradox, one of most well known paradoxes of time travel. It’s a pretty simple scenario; you go back in time to kill your grandfather. The problem to this is that if your grandfather is dead, then he wouldn’t be able to give birth to your parents. Without your parents existing, then you can’t exist. Yet you were able to travel back in time to kill your grandfather.

But we also have theories to put down these paradoxes. The Novikov self-consistency principle says that anything a time traveler does in the past, is already represented in the present time. This principle believes the Universe “prohibits” inconsistency, that free-will of a time traveler is limited when he/she travels. Another possibility is that maybe one does can do anything they want in the past. But changing anything in the past will lead to a different parallel Universe. By changing what you do in the past, you essentially split the universe into two scenarios. The future you are from will stay the same because that was already determined from the past. But your new change in the past, will create another world where the future will be different because of that change. So if you were to go back and somehow save the dinosaur species from extinction, there would still be no dinosaurs in the present day. This is because the instant you save the dinosaurs, you have essentially split the Universe to go on two alternative paths; one path with a world of dinos; another with just humans.

All in all, these paradoxes clash with the idea of traveling back in time. If we want to resolve these issues, we need to think outside the box, such as with Novikov self-consistency principle. Or we need to start finding evidence for parallel universes. These paradoxes pose more questions that physicists and astronomers need to answer. It creates more opportunities to learn and discover about new things.

Sources:

"3 Time Travel Paradoxes!!" YouTube. YouTube. Web. 25 Apr. 2015.
"Time Travel Simulation Resolves." Scientific American Global RSS. Web. 25 Apr. 2015.

- Eric Lee

Dark Matter Detection

Along with the numerous proposed candidates for dark matter, many varying dark matter detection methods have been developed, too. Currently, most of the search is now directed towards weakly interacting massive particles, or WIMPs. The two methods of dark matter detection currently used are very different and as such revolve around completely different facilities, so they will be talked about separately. The most obvious method of proving the existence of dark matter is called direct detection, and it involves finding living WIMPs in a real environment. The other method, indirect detection, instead searches for the particles left behind by a decayed WIMP.

Direct detection generally involves large facilities working in large scales to increase the chance that a stray WIMP will be detected. There are two types of direct detection technologies currently used: cryogenic detectors and noble liquid detectors. Cryogenic detectors operate at temperatures close to absolute zero and are able to detect random particles hitting a crystal absorber by the heat they give off. One of the most famous cryogenic detectors is CDMS, or the Cryogenic Dark Matter Search. Despite the generic name, the program has had 11 possible detections of WIMPs, from 2009 to 2013. The other kind of detection technology, noble liquid detectors, are able to detect particles by the light they produce upon hitting a liquid noble gas, like xenon. Another famous noble liquid detector is LUX, the Large Underground Xenon experiment. LUX is able to detect WIMP collisions with xenon atoms, but also can distinguish neutron collisions with actual WIMP collisions. Both of these detection methods require very isolated facilities far underground to reduce the effect of cosmic rays on experiments.

Indirect detection hinges on the existing theories of supersymmetry and rely on the prior knowledge of a WIMP's construction and degradation. WIMPs should be able to decay into standard model particles, specifically gamma-rays, so many gamma-ray-capable space telescopes search for areas of high gamma-ray concentration. For instance, the Fermi Gamma-ray Space Telescope's discoveries posited that a large amount of gamma-ray radiation from the center of the Milky Way could be because of WIMP annihilation. Another experiment, PAMELA, found an abundance of positrons and cosmic rays, meaning it possibly witnessed WIMP annihilation, too.

Sources:

CDMSCE @ UC Irvine
Shadow Universe by Corey S. Powell

- Jacob Lee

The History Recorded in Mars’ Meteorites

Mars resembles the Earth in many ways, including its day length, its temperature, and its gravity, thus many people consider the possibility that one day we may inhabit it. However, there are many mysteries that scientists would have to solve before determining whether Mars is capable of supporting life. If they ultimately show that life once existed on Mars, it will confirm that life can exist on other planets, even if might not be plausible for life to exist now or in the future on Mars itself. Scientists approach this question from several directions. One of them is studying the SNC meteorites, which originated on Mars.

Most of the meteorites from Mars fall into one of three groups –Shergotty, Nakhla, and Chassigny –thus people use the term SNC meteorites to refer to meteorites from Mars. These meteorites contain similar compositions and have similar structures, thus when petrologists first studied them, they speculated that they might have come from the same “parent body.” Even though they come from the same planet, they also differ in many ways. Most SNC meteorites belong to the shergottite category, which is a kind of basaltic meteorite consisting mostly of pyroxenes and relic plagioclases. Some of the Martian meteorites fall into the category of nakhlites. These meteorites are clinopyroxenes, which are monoclinic pyroxenes and are either calcic or sodic, and they contain augite, olivine abundant in iron, titanium-rich magnetite and interstitial and glassy material that was formed when the meteorite was formed. “The nakhlites have preserved some of the clearest traces of aqueous alteration within the parent rocks on Mars” (Martian Meteorites). Last but not least, chassigny is a cumulative of dunite, containing more than 90 percent of olivine, with pyroxene, chromite and plagioclase making up the rest (Martian Meteorites).

Since the SNC meteorites share so many similar features, researchers were certain that they originated on the same planet. They also speculated that they came from Mars, but not until 2000 were they confident that the SNC meteorites indeed originated on the Red Planet. According to Allan Treiman and his fellow researchers, the 14 SNC meteorites that were identified at that time “contained traces of gas which is similar in elemental and isotopic compositions to the modern Martian atmosphere as measured by Viking landers on Mars and spectroscopy from Earth.” Specifically, the EETA 79001, which is in the class of shergotite, is the first SNC meteorite that found to contain the compositions that were also identified on Mars. It has glass inclusions that contain rare nitrogen isotopic compositions, which was also found in the Martian atmosphere by the Viking spacecraft in 1976. As Treiman said, since Mars has such a unique composition, having a similar composition with it is a strong indication that the SNC meteorites came from Mars. If they are not from Mars, “it (the planet that SNC meteorites actually came from) would have to be substantially identical to Mars as it now is understood”, Treiman confirmed.

Sources:

http://www.nhm.ac.uk/research-curation/research/projects/martian-met/meteorites.html
http://mars.nasa.gov/mer/mission/tl_surface.html
http://meteorite.unm.edu/site_media/pdf/MarsMeteorites.pdf
J. Eberhart. “A Meteorite Messenger from the Moon?” Science News. 27 Nov 1982.

http://meteorites.wustl.edu/lunar/stones/lm_alha81005_s83-34612.jpg

- Jiaxuan Liu

SpaceX vs. United Launch Alliance

Nowadays, SpaceX is known as one of the larger companies within the space travel industry. One of SpaceX’s main ventures is launching rockets. Of course, there are other launch companies who provide similar services. The largest competiting company is the United Launch Alliance (ULA), a 50-50 joint venture owned by Lockheed Martin and Boeing. Since ULA’s primary products are rockets that launch satellites or other objects into space, it is natural for them to be competitors of SpaceX. Currently, ULA has three rockets: the Atlas V, Delta II, and Delta IV, most of which are sold to the United States government. Controversy with arose in 2014 when SpaceX’s founder, Elon Musk, claimed that ULA rocket launches cost the government $460 million dollars each, opposed to SpaceX’s relatively low cost of $90 million dollars per launch. SpaceX protested by stating that the process for contracting the Air Force’s launches should be competitive, rather than uncontested, as ULA was being handed large launch contracts without the consideration of SpaceX (Leopold). ULA was not very happy about this, and responded by claiming that their launches were around $160 million dollars apiece (Gruss). Also, CEO Tory Bruno claimed that it was risky to rely on SpaceX for national security launches (Davenport). By trying to force their way into the more lucrative launching business, SpaceX is trying to gain more funding and to display their newfound strength in space travel. Even though ULA is newer, Lockheed Martin and Boeing are old and established companies that have much more history than SpaceX.

SpaceX's Falcon 9 on the left, and
ULA's Delta IV on the right.

Yet, SpaceX’s claims have managed to scare ULA into making some fairly drastic changes. These changes start with cutting launch costs in order to compete with SpaceX, as well as developing a new launch system. Unlike SpaceX, ULA buys many of its parts from other producers, which is problematic. This is because the RD-180 engine, used for the Atlas V, is made in Russia. Due to tense relations with Russia over affairs in Ukraine, the United States government has banned the RD-180 engine, leaving ULA with only five RD-180s for about forty launches through 2024 (Gruss). This is an important difference between SpaceX and ULA: SpaceX is unaffected by problems with suppliers, since they have the capabilities to manufacture their own products, while ULA is susceptible to restrictions and problems from external forces. This is how SpaceX will continue to keep their prices low, and why it will take a while for ULA to catch up to SpaceX, if they can even catch up.

That being said, ULA is also working on some projects of their own. One such project is to address the aforementioned problems with the engines. There are currently plans to develop a replacement engine for the RD-180, the BE-4, built by Amazon founder Jeff Bezos’ company, Blue Origin. There are currently plans for testing of the BE-4 in 2016, with the first flight being in 2019 (ULA). The BE-4 will be much stronger than SpaceX’s current Merlin 1D, with a planned thrust of 2,400 kilonewtons, which will be competitive with SpaceX’s planned Raptor engine. Another project that ULA is working on to compete with SpaceX is the Vulcan rocket. The Vulcan is planned to be much cheaper than the Delta and Atlas models that ULA currently uses (about $100 million dollars), and will use the BE-4 engine that is currently being developed (Clark). There are also some plans to have degree of reusability, perhaps using parachutes and helicopters to recover stages of rocket, but these ways would not be tested until the 2020s (Bruno). Clearly, the big unveiling used to display their plans is a way to relieve pressures from SpaceX as within a couple of years, SpaceX might not just be slightly ahead of ULA’s current capabilities—they might be far ahead.

Clearly, SpaceX fares well against ULA. By maintaining a low launch cost, SpaceX is more able to obtain launch contracts with companies as well as attract interest from the government. Also, when SpaceX is eventually to launch people to Mars reliably, a lower cost will mean that more people will be able to go to Mars and at a faster rate. This lower cost is due to their ability to make almost, if not everything, on their own. Another benefit is that they are extremely efficient in planning and building their projects. Currently, it has been 13 years since the inception of SpaceX, and within these 13 years, tremendous progress has been made to further space travel. From rockets to space capsules, SpaceX is beginning to take a leading position in the industry. Presumably, the smaller size of SpaceX allows for a more efficient workspace; all of the engineers are together in one place, so the development process is greatly streamlined. Therefore, the so-called competitors of SpaceX do not really pose any kind of immediate threat as they lack the capabilities that SpaceX currently possesses.

Sources:

http://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?no-ist
http://defensesystems.com/articles/2014/04/28/spacex-protest-air-force-ula-contract.aspx
http://spacenews.com/40637news-from-the-30th-space-symposium-responding-to-critics-ula-discloses/
http://www.washingtonpost.com/blogs/the-switch/wp/2015/03/02/ula-ready-to-compete-against-elon-musks-space-startup-ceo-says/
http://spacenews.com/air-force-wary-of-swapping-ulas-monopoly-for-a-different-sort-of-dependence/
http://www.ulalaunch.com/ula-and-blue-origin-announce-partnership.aspx
http://www.spacex.com/news/2014/10/16/spacex-completes-100th-merlin-1d-engine
http://spaceflightnow.com/2015/04/22/ula-needs-commercial-business-to-close-vulcan-rocket-business-case/
http://spaceflightnow.com/2015/04/13/ula-unveils-its-future-with-the-vulcan-rocket-family/

- Kevin Li