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Place one clock at the top of a mountain. Place another on the beach. Eventually, you'll see that each clock tells a different time. Why? Time moves slower as you get closer to Earth, because, as Einstein posited in his theory of general relativity, the gravity of a large mass, like Earth, warps the space and time around it.
Scientists first observed this "time dilation" effect on the cosmic scale, such as when a star passes near a black hole. Then, in 2010, researchers observed the same effect on a much smaller scale , using two extremely precise atomic clocks, one placed 33 centimeters higher than the other. Again, time moved slower for the clock closer to Earth.
Physics without time
Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.
"If I observe the microscopic state of things," writes Rovelli, "then the difference between past and future vanishes … in the elementary grammar of things, there is no distinction between 'cause' and 'effect.'"
Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.
Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.
"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the Financial Times. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."
The strange subjectivity of time
Time moves differently atop a mountain than it does on a beach. But you don't need to travel any distance at all to experience strange distortions in your perception of time. In moments of life-or-death fear, for example, your brain would release large amounts of adrenaline, which would speed up your internal clock, causing you to perceive the outside world as moving slowly.
Another common distortion occurs when we focus our attention in particular ways.
"If you're thinking about how time is currently passing by, the biggest factor influencing your time perception is attention," Aaron Sackett, associate professor of marketing at the University of St. Thomas, told Gizmodo. "The more attention you give to the passage of time, the slower it tends to go. As you become distracted from time's passing—perhaps by something interesting happening nearby, or a good daydreaming session—you're more likely to lose track of time, giving you the feeling that it's slipping by more quickly than before. "Time flies when you're having fun," they say, but really, it's more like "time flies when you're thinking about other things." That's why time will also often fly by when you're definitely not having fun—like when you're having a heated argument or are terrified about an upcoming presentation."
One of the most mysterious ways people experience time-perception distortions is through psychedelic drugs. In an interview with The Guardian, Rovelli described a time he experimented with '___'.
"It was an extraordinarily strong experience that touched me also intellectually," he said. "Among the strange phenomena was the sense of time stopping. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing any more. It was a total subversion of the structure of reality."
It seems few scientists or philosophers believe time is completely an illusion.
"What we call time is a rich, stratified concept; it has many layers," Rovelli told Physics Today. "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."
Time is Elastic
Yes, Einstein published general relativity in 1915 but few people believed it until the first experimental confirmation in 1919, after which people started believing it and with each passing experimental confirmation it became more clear that the theory was consistent with observations and experiments. Perhaps one of the most amazing experimental confirmations was this one in 2010 mentioned in the OP article, which didn't require all the variables in the Hafele–Keating experiment:
originally posted by: Gothmog
We have known this since 1971...
The Hafele–Keating experiment
Actually , before then .
Cause Einstein....
Now, physicists at the National Institute of Standards and Technology (NIST) have measured this effect at a more down-to-earth scale of 33 centimeters, or about 1 foot, demonstrating, for instance, that you age faster when you stand a couple of steps higher on a staircase.
originally posted by: Gothmog
We have known this since 1971...
The Hafele–Keating experiment
Actually , before then .
Cause Einstein....
originally posted by: RavenSpeaks
Time is Elastic
I'm thinking that our sense of time / reality has
something to do with the double helix nature of our DNA.
Sort of like how its possible to create a "time delay"
reverb unit using springs.
originally posted by: Arbitrageur
a reply to: Gothmog
I'm not sure how you think the radiation would affect time but it was done in a lab so there wouldn't be much change in radiation over the height of .5 meter, and even if there is, in which direction would it increase? The ground emits radiation too, some places more than others.
Technically, the clocks that measured the time difference between your head and your feet are called "Optical Clocks" because they measure vibrations in atoms that occur at optical frequencies (ultraviolet). So if the measurement is made inside a lab and the lab is blocking UV light from outside the lab, it seems illogical to suppose that UV light from outside the lab is affecting the optical clock results. This is about NIST's most accurate optical clock used in the experiment:
originally posted by: Gothmog
originally posted by: Arbitrageur
a reply to: Gothmog
I'm not sure how you think the radiation would affect time but it was done in a lab so there wouldn't be much change in radiation over the height of .5 meter, and even if there is, in which direction would it increase? The ground emits radiation too, some places more than others.
You do know they used ATOMIC CLOCKS , yes ?
So unless you can explain how UV radiation is getting into the lab from outside, I fail to see how you think external radiation will affect the optical UV frequency used by the optical atomic clock.
The logic clock is based on a single aluminum ion (electrically charged atom) trapped by electric fields and vibrating at ultraviolet light frequencies, which are 100,000 times higher than microwave frequencies used in NIST-F1 and other similar time standards around the world. Optical clocks thus divide time into smaller units, and could someday lead to time standards more than 100 times as accurate as today's microwave standards.
With the optical clocks, the theory of relativity wasn't only tested with a height difference, it was also tested with a velocity difference where there was no difference in height, and that experiment also matched theoretical predictions, so there's no way your radiation versus height idea could explain that result with the velocity difference.
Technically, the clocks that measured the time difference between your head and your feet are called "Optical Clocks" because they measure vibrations in atoms that occur at optical frequencies (ultraviolet).