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Nasa and its scientists are searching for clues on the structure of space and time to unlock secrets of the universe. Their mission on light travelling at the speed of light is questionable.
They have a special telescope called The Fermi Gamma-ray space telescope and with its recordings of two photons journey across seven billion light years of space there may be other answers out there.
Einstein's Theory of Relativity, which describes space and time as a smooth fabric that's distorted, or bent by massive objects, has been a spectacularly successful explanation of gravity and the large scale behaviour of the universe.
Where Quantum Mechanics another spectacularly successful model describes the workings of atoms subatomic particles and some of the fundamental forces of nature. Scientists have never been able to reconcile the two.
Both Relativity and Quantum Mechanics are equally fundamental in their own regimes. With the observations from the Fermi telescope of the two photons, scientists are a step closer of achieving the goal of having a theory of everything that combines the most successful aspects of Quantum Mechanics and Relativity into one unified theory.
To add to this puzzle, other telescopes have observed gamma rays with different wavelengths arriving at Earth at different times.
According to Einstein's Special Theory of Relativity, all forms of electromagnetic radiation from radio and infrared, to visible light, to X-rays and even gamma-rays moves at the same speed.
So what would explain these differences in arrival times?
One simple idea is that maybe the photons were just emitted at different times.
More interestingly though, maybe there was something in the very fabric of space that was causing the higher-energy particle to slow down.
If this is true, could Einstein have been wrong?
Could a higher-energy particle move slower than the speed of light?
Scientists observed a gamma-ray burst. A gamma-ray bust is a huge explosion. That gamma-ray burst produced a large number of photons, one of which had enormous energy, and very short wavelengths. Those photons traveled seven billion years to reach us, and yet the highest energy, the shortest wavelength of photon arrived within 900 milliseconds of the lower-energy photons. That's a little bit like racing two speed-boats, one through water and the other through molasses, and having them arrive at the same time; it just doesn't happen.
Because Fermi saw no delay in the arrival time of the two photons, it confirms that space and time is smooth and continuous as Einstein had predicted. And it shuts the door on several theories of everything that had predicted that space and time might be foamy enough to interfere with light.
Fermi eliminated some ideas from the mix, and that means scientists are one step closer to potentially unifying Relativity and Quantum Mechanics.
Science is a process of elimination, and unless we keep eliminating, we may never know if this Theory of Everything actually exists, hidden in the math of our universe.
But for now, we'll have to keep searching for clues beyond our small planet, because the answers truly lie among the stars.