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Perhaps you are one of those who, when they hear news, ask themselves, "How will they know that?"
We were told that the moon is moving away from the Earth. And it's not that we doubt it, but how do they know it?
Scientists Adam Rutherford and Hannah Fry, who investigate the BBC's public doubts, found the answer to our question in a somewhat convoluted way. do not worry, we will find out, but on the way we will discover amazing things.
It all started with a question from listener Eddie Griffith:
"The other day I was watching the James Bond film Goldfinger .He boasts that his laser is powerful enough to project its light onto the moon, is it really possible and how powerful this laser should be? "
" The most devilish opponent of James Bond, an evil genius with a thirst for gold ". For those who do not remember the plot of this film, Auric Goldfinger is a devilish megalomaniac obsessed with gold and plans to blow up a bomb inside Fort Knox – where since 1937 a large part of the gold reserves have been stored in the United States – so that their own gold reserves are more valuable.
James Bond learns the plan, but they remove it and take it to Goldfinger's secret lair, where they extend it and attach it to a gold table.
After having informed of the power of his laser, Goldfinger lights the burning beam and shifts between Bond's legs in the direction of his. But let's go back to the question, that it was not exactly if a laser could burn the private parts of the famous spy, but if we could see the light of its ray on the surface of the moon if it were projected in his address.
C What power would it take for to reach the moon?
Megawatts? Terawatt? Petawatts? Prepare for size figures like 1,000,000,000,000. BBC MUNDO / Getty Images
"I had very little time to prepare the answer since they asked me the question, so it's only an estimate, "warns physicist Andrew Pontzen.
"I suppose if you want to create a point of light on the surface of the moon, you would need a laser with a power of 200 megawatts."
"A watt is the measurement used in light bulbs, so to have a perspective, today a good energy saving light bulb is 10 watts.Therefore, this laser has to be 20 million times stronger. 19659002] And will we have such powerful lasers? Of course, and more!
One of the most powerful in the world is found in Didcot, UK, and is called Super Intense Gemini Laser. What would happen if you pointed your laser on the moon?
"It's probably too powerful," says physicist Ceri Brenner
"His power is about half petawatt ". line laser ” width=”976″ height=”50″/>
Explanation of urgency : A petawatt (PW) are 10 high at the power of 15 watts or, which is the same, [19659033] 1,000 terawatts or 1,000 billion (1,000,000,000,000,000) watts. A Petawatt laser generates this power for an interval of a few femtoseconds .
Explanation of urgency II : A femtosecond is the unit of time equivalent to one billionth part of a second, it is deci r, that in a second there is a billion billion femtoseconds. They correspond to as many seconds as the seconds correspond to 100 million years (ie 3,153,600,000,000,000 seconds).
But it should not be very powerful for ] reach the Moon?
"When laser light is so powerful, it is problematic to cross the Earth's atmosphere," says Brenner. "The laser would burn the air when it crossed it."
Excuse me? How does the atmosphere burn?
"When traveling, the intensity of light is such that it simply converts air into plasma."
Would it burn the sky?
this would generate a powerful beam. Those are the rays: the plasma channels, "replies Brenner, with the same simplicity as that of others explaining how to boil an egg
So be careful when pulling powerful lasers. BBC MUNDO / Getty Images
Anyway,
Better to return to this 200 megawatt laser … although once you add extra effects to compensate for things like diffraction in the Earth's atmosphere that spreads light, you might need gigawatt .
It is basically equivalent to the power of a nuclear generator. And probably, the laser should be about 15 meters in diameter.
But after they left our mouths open talking about petawatts and femtoseconds, it does not seem so bad anymore.
The man who fires the lightning at Luna
Trying to finally fulfill the mission of solving the doubt of the listener, Rutherford and Fry have discovered a physicist who actually pulls laser pulses on the moon .
He's called Tom Murphy, of the University of California at San Diego, USA, and is engaged in what they call "laser measurement experiments."
Tom Murphy casts rays of light toward the moon. BBC
Murphy uses a gigawatt laser located at the top of a mountain in New Mexico and shoots impulses on mirrors left on the moon by astronauts from three Apollo program missions and two Soviet lunar rovers.
Note that when the light reaches our natural satellite, it is so weak that you need telescopes to see it … and unlike Goldfinger – there does not use his laser for criminal purposes [19659012] but scientific.
"Indeed, we use it for scientific purposes as to try to prove if the general theory of relativity correctly describes the lunar orbit ," Murphy confirms .
For this, they must measure far from the moon.
"It's a simple idea: we send short pulses of light traveling to the Moon's reflectors.These impulses return to Earth and we simply measure how much time the round trip took , and we use the speed of light to convert it into distance. "
And so it is that the Moon is known to be moving away .
"The moon is slowly migrating as a result of tidal acceleration, moving at an average of about 3.8 centimeters per year from the Earth."
But there is Is there a reason to worry? Because we do not want it to go away …
"No, the effect diminishes as it's". he moves away, so this one is not a mechanism that will let him escape ", says the physicist.] Child Looking at the Moon" width = "624 "height =" 700 "/>
What a relief! BBC MUNDO / Getty Images
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