In a old outer space film, jody foster says hydagen x pi. what does tha mean?

Answer 1

Most of these others are right about the hydrogen (alpha) emission feature at 21 cm. But I'll just add a couple of details, hopefully for clarification. The spectrum of each element can be shown as a graph from violet to red, with spikes at the points where it emits the most. Hydrogen is the most common element. The 21 cm spike is very pronounced and at a frequency which would be good for interstellar transmission. So a culture might choose something like this as a frequency. Why? Suppose you knew you had to meet somebody in New York City but you had no idea where, and the other person knows you don't. Where would you go to increase the odds of meeting the person? You see? The choices gravitate toward common landmarks. That's what the hydrogen line is: the Empire State Building of interstellar EMR.
Now why pi times it? Because that frequency is very "loud." That's why it's a spike. So it would interfere with a signal if you used it to send one. So multiply it by some number that another technical civilization might guess. Pi. Another landmark value. Seeing this transmission being sent on "pi times hydrogen" means it is almost certainly of intelligent origin.

Answer 2

The signal from space is being transmitted at a radio frequency equal to the emission of hydrogen times the constant pi (ratio of a circle's circumference to its diameter). This is significant because hydrogen is the most common element in the Universe, and pi is a very basic and universal constant. The signal incorporated both of these so it would be easier to find by someone searching the skies for alien transmissions, since there are so many radio frequencies -- this would help to narrow the search, since you could assume that anyone looking for your message would have a basic understanding of science. It would be unlikely for a natural phenomenon to give off a radio signal with a regular pattern at this specific frequency. (The signal was also being pulsed in groups of prime numbers, an unmistakable sign of intelligence).

Answer 3

The movie was "Contact," based upon the novel by Carl Sagan.

Basically, an alien society had sent us a transmission on a particular frequency. They chose a frequency that was based upon a universal mathematical concept that any other civilization would be able to recognize, no matter how strange and foreign they might be.

In this case, it was the "hydrogen line" (which is the frequency of the spectral line created by hydrogen = 1420.40575 MHz) times pi (which is the ratio of a circle's diameter to its circumference = 3.14159), which results in 4.4623 GHz.

Answer 4

It's the spectrum wavelength or frequency at which the message was being transmitted. Think of the numbers on your radio dial. Those are all frequencies. The frequencies on your car radio are part of a much longer ELECTROMAGNETIC SPECTRUM.

The wavelengths of your radio dial, or Jody Foster's messages from the aliens, are measured in units of energy, call hertz. A gigahertz is one billion hertz. Jody's signal is more than four billion gigahertz:: 4.4623GHZ.

With this knowledge Jody can tell the other radio astronomy facilities where to go on the "listening dial" to hear the alien message.

Answer 5

That would be "Contact." Ellie Arroway says "hydrogen times pi" suggesting the microwave frequency is pi times 1.42040575 GHz, the hydrogen 21 cm line of its hyperfine spin-flip transition.

That would be about 4.46233627 GHz - a perfectly reasonable microwave communication frequency of 6.68 cm wavelength and indicative of artificial orgin for combining two fundamental universal constants.

Do you have your primer?

Answer 6

Hi. Hydrogen emits radiation when heated at certain frequencies. Pi is a universal constant. She had guessed that any signals heard would be the frequency of hydrogen emission times pi.