Realistic Elements of Contact’s Depiction of Alien Communication:

1. Use of Radio Waves for Interstellar Communication:

In the film, the message from an alien civilization is transmitted using radio waves, which is highly plausible. Radio waves are a form of electromagnetic radiation that can travel vast distances through space with little interference. They are also relatively easy to generate and detect, making them an ideal medium for long-range communication between civilizations.

Why Radio Waves? Radio waves are not significantly absorbed by the interstellar medium (i.e., the gas and dust between stars) and can travel through space at the speed of light. This is why many real-world projects, such as the Search for Extraterrestrial Intelligence (SETI), focus on scanning the skies for radio signals. SETI’s Allen Telescope Array, for example, is designed specifically to detect these signals. The rationale behind this is that any technologically advanced civilization might use radio waves because they are simple to generate and can carry large amounts of information over long distances.

"The Water Hole": Scientists expect that any communication from extraterrestrial intelligence would likely occur in the "water hole" part of the radio spectrum (between 1,420 and 1,666 MHz), where cosmic noise is minimal, and natural sources like hydrogen and hydroxyl molecules emit radio waves. This frequency band would make the signal stand out from the background noise, just as it does in Contact, where the signal from Vega is immediately recognized as artificial.

2. Prime Numbers and Mathematical Encoding:

The aliens in Contact begin their message by transmitting prime numbers, a sequence that any intelligent civilization familiar with mathematics could recognize. This concept is realistic because prime numbers are not naturally produced by physical processes, making them an ideal “attention-getter.” They serve as a universal signal that intelligent life is responsible for the communication.

In fact, the idea of using prime numbers or other mathematical patterns in potential alien communication predates Contact. In the 1974 Arecibo message sent toward the M13 star cluster, scientists encoded numbers and symbols representing basic biological and chemical information. The idea is that math is a universal language that transcends cultural differences, making it a logical starting point for interstellar communication.

3. Layered Messages and the Use of a Rosetta Stone Approach:

In the film, after the initial transmission of prime numbers, a more complex message is revealed, containing blueprints for building a machine. This idea of a multi-layered message is scientifically plausible. Any communication from an extraterrestrial civilization might need to be structured in such a way that it could be progressively decoded, using simpler elements to help unlock more complex information. This “Rosetta Stone” approach assumes that the aliens would try to communicate in a way that gradually teaches humans how to interpret their message.

Historical Context: The Pioneer and Voyager spacecraft, for example, were equipped with plaques and records designed to be decoded by an alien civilization. The idea was to use universally recognizable scientific and mathematical principles to communicate fundamental information about humans and Earth.

4. Detection Methods and International Collaboration:

The film realistically portrays how a signal from an alien civilization might be detected using large radio telescope arrays, like the Very Large Array (VLA) in New Mexico, which is a real facility. Additionally, the international collaboration and involvement of various governments and scientific organizations in decoding and interpreting the signal reflect how such a discovery would likely unfold in reality.

SETI’s Real-World Efforts: SETI researchers rely on similar methods, using large arrays of radio telescopes to scan the sky for signals that could be from an alien civilization. While no definitive signal has been found yet, the procedures depicted in Contact—the excitement, scrutiny, and cross-institutional collaboration—are grounded in how the scientific community might react to a real discovery.

Speculative or Unrealistic Aspects of Contact:

1. The Star Vega as a Source:

In Contact, the signal originates from Vega, a star located about 25 light-years away from Earth. While Vega is relatively close to Earth in cosmic terms, it is unlikely to host life or be home to an advanced civilization. Vega is a young star (about 455 million years old) and much hotter than the Sun, which means it is less likely to have habitable planets or life as we know it. The choice of Vega in the film is more for narrative convenience than scientific plausibility, as the star's age and conditions make it an unlikely candidate for supporting an advanced civilization.

2. Two-Way Communication and Signal Delays:

One of the significant issues with interstellar communication, which Contact doesn't address in detail, is the time delay involved in sending and receiving signals. Radio waves travel at the speed of light, so a message sent from Vega would take 25 years to reach Earth. Any response would take an additional 25 years to return to Vega. This means that even simple two-way communication would be incredibly slow and impractical on human timescales.

Real-World Limitations: While receiving a signal is plausible, maintaining a dialogue with a civilization that far away would be exceedingly difficult due to these long delays. Any communication with a civilization tens or hundreds of light-years away would be more like sending messages in a bottle than holding a conversation.

3. The Construction of the Machine:

In Contact, the message includes blueprints for building a machine that facilitates travel through wormholes. While wormholes are a theoretical possibility in general relativity, there is no known way to create or stabilize a traversable wormhole using our current technology. The depiction of the machine in the film is more speculative science fiction than grounded science, as it would require exotic matter with negative energy density to keep the wormhole open—something we have no evidence exists.

Wormholes and Exotic Physics: The concept of wormholes has been explored by physicists like Kip Thorne, but the idea of using them for practical travel remains speculative at best. The construction of such a machine, as shown in Contact, is far beyond the realm of what is currently possible, and the movie takes liberties with the science here for dramatic effect.

Other Plausible Methods of Alien Communication:

1. Laser and Optical Communication:

While radio waves are a logical choice for interstellar communication, another possibility is the use of lasers. Lasers can carry more data and are less likely to be lost in cosmic noise. Some scientists have proposed searching for brief pulses of laser light from distant stars, which could indicate an alien civilization using optical communication. This method would be faster and more efficient than radio waves but requires very precise targeting.

Optical SETI: Projects like Optical SETI (OSETI) are dedicated to searching for extraterrestrial laser pulses. A civilization might choose lasers because they allow for high-speed, high-density data transmission over long distances.

2. Gravitational Waves:

Though purely speculative at this stage, some scientists have suggested that an advanced civilization might use gravitational waves to communicate. Unlike electromagnetic waves, gravitational waves are distortions in spacetime itself and can travel vast distances without being affected by matter. However, detecting and interpreting gravitational wave signals for communication would require technology far beyond what we currently possess.

3. Self-Replicating Probes (Bracewell Probes):

Instead of relying on electromagnetic communication, an advanced civilization might send self-replicating probes (sometimes called Bracewell probes) to explore and communicate with distant planets. These probes could physically travel across the galaxy, arriving at distant stars and transmitting data directly to any civilizations they encounter. While we have not detected any such probes, this concept is a plausible alternative to long-distance radio communication.

Conclusion:

Contact provides a largely scientifically plausible portrayal of how humans might receive a message from an extraterrestrial civilization, particularly through the use of radio waves and mathematical encoding. The film aligns well with real-world SETI efforts and theoretical considerations for first contact. However, certain aspects—such as the construction of a wormhole machine and the rapid two-way communication—veer into speculative territory. While radio communication is currently the most realistic method, other possibilities, such as optical signals, gravitational waves, or self-replicating probes, also offer scientifically plausible alternatives for how we might eventually contact or be contacted by alien civilizations.

(http://www.autoadmit.com/thread.php?thread_id=5598386&forum_id=2...id.#48112164)