Redshift and Distance in the Expanding Universe
Last week, we began talking about understanding the size of the Universe, and we continued this week with some information on distances and motion in the Universe. This brings us to my favorite application, which leads to the Hubble expansion: Redshift. You see, whenever an atom or molecule emits light, it gives off that light at a very few particular wavelengths.
Natural resources
The Earth's natural resources are vital to the survival and development of the human population. These resources are limited by the Earth's capability to renew them. Although many effects of overexploitation are felt locally, the growing interdependence of nations, and international trade in natural resources, make their demand and sustainable management a global issue.
Faster-than-light
Faster-than-light (also superluminal or FTL) communication and travel are the conjectural propagation of information or matter faster than the speed of light. According to the current scientific theories, matter is required to travel at slower-than-light (also subluminal or STL) speed with respect to the locally distorted spacetime region. Apparent FTL is not excluded by general relativity; however, any apparent FTL physical plausibility is speculative. Examples of apparent FTL proposals are the Alcubierre drive and the traversable wormhole.
New supernova analysis reframes dark energy debate
The accelerating expansion of the Universe may not be real, but could just be an apparent effect, according to new research published in the journal Monthly Notices of the Royal Astronomical Society. The new study—by a group at the University of Canterbury in Christchurch, New Zealand—finds the fit of Type Ia supernovae to a model universe with no dark energy to be very slightly better than the fit to the standard dark energy model. Dark energy is usually assumed to form roughly 70% of the present material content of the Universe. However, this mysterious quantity is essentially a place-holder for unknown physics. Current models of the Universe require this dark energy term to explain the observed acceleration in the rate at which the Universe is expanding. Scientists base this conclusion on measurements of the distances to supernova explosions in distant galaxies, which appear to be farther away than they should be if the Universe's expansion were not accelerating.
How Space Shuttles Work"
In its nearly 30-year history, the space shuttle program has seen exhilarating highs and devastating lows. The fleet has taken astronauts on dozens of successful missions, resulting in immeasurable scientific gains. But this success has had a serious cost. In 1986, the Challenger exploded during launch. In 2003, the Columbia broke up during re-entry over Texas. Since the Columbia accident, the shuttles have been grounded pending redesigns to improve their safety.
Intergalactic travel
Intergalactic travel is space travel between galaxies. Due to the enormous distances between our own galaxy the Milky Way and even its closest neighbors — hundreds of thousands to millions of light-years — any such venture would be far more technologically demanding than even interstellar travel. Intergalactic distances are roughly one-million fold (six orders of magnitude) greater than their interstellar counterparts. The technology required to travel between galaxies right now is far beyond humanity's present capabilities, and currently only the subject of speculation, hypothesis, and science fiction.
Doppler effect
Change of wavelength caused by motion of the source. An animation illustrating how the Doppler effect causes a car engine or siren to sound higher in pitch when it is approaching than when it is receding. The red circles represent sound waves. For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted.[1] The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered.
Krasnikov tube
A Krasnikov tube is a speculative mechanism for space travel involving the warping of spacetime into permanent superluminal tunnels. The resulting structure is analogous to a wormhole with the endpoints displaced in time as well as space. The idea was proposed by Serguei Krasnikov in 1995.[1] Structure[edit]
Waves, motion and frequency: the Doppler effect
The frequency of a wave-like signal - such as sound or light - depends on the movement of the sender and of the receiver. This is known as the Doppler effect. Some of its manifestations, we know from everyday life, such as a fire engine's siren abruptly changing pitch as the engine passes by; others are of interest in astronomy and astrophysics. The purpose of this spotlight text is to take a closer look at what the Doppler effect is all about. Pulses sent out and received We will start with a very simple set-up, which you can see in the following animation.
