IS TIME AN ILLUSION??
Blog#393
Wednesday, April 17th, 2024.
Welcome back,
Why is time controversial? It feels real, always there, inexorably moving forward. Time has flow, runs like a river. Time has direction, always advances. Time has order, one thing after another. Time has duration, a quantifiable period between events. Time has a privileged present, only now is real. Time seems to be the universal background through which all events proceed, such that order can be sequenced and durations measured.
The question is whether these features are actual realities of the physical world or artificial constructs of human mentality. Time may not be what time seems — this smooth unity without parts, the ever-existing stage on which all happenings happen.
To appreciate time is to feel the fabric of reality. I interview physicists and philosophers on my public television series, "Closer to Truth," and many assert that time is an illusion. What do they mean that time is "not real?"
Huw Price, professor of philosophy at Cambridge University, claims that the three basic properties of time come not from the physical world but from our mental states: A present moment that is special; some kind of flow or passage; and an absolute direction.
"What physics gives us," Price said, "is the so-called 'block universe,' where time is just part of a four-dimensional space-time … and space-time itself is not fundamental but emerges out of some deeper structure."
We sense an "arrow" or direction of time, and even of causation, he said, because our minds add a "subjective ingredient" to reality, "so that we are projecting onto the world the temporal perspective that we have as agents
Think of the block universe, which is supported by Einstein's theory of relativity, as a four-dimensional space-time structure where time is like space, in that every event has its own coordinates, or address, in space-time.
Time is tenseless, all points equally "real," so that future and past are no less real than the present.
So, are we being misled by our human perspectives? Is our sense that time flows, or passes, and has a necessary direction, false? Are we giving false import to the present moment?
"We can portray our reality as either a three-dimensional place where stuff happens over time," said Massachusetts Institute of Technology physicist Max Tegmark, "or as a four-dimensional place where nothing happens [‘block universe’] — and if it really is the second picture, then change really is an illusion, because there's nothing that's changing; it's all just there — past, present, future.
"So life is like a movie, and space-time is like the DVD," he added; "there's nothing about the DVD itself that is changing in any way, even though there's all this drama unfolding in the movie. We have the illusion, at any given moment, that the past already happened and the future doesn't yet exist, and that things are changing. But all I'm ever aware of is my brain state right now. The only reason I feel like I have a past is that my brain contains memories.
"Time is out there," said Andreas Albrecht, a theoretical cosmologist at the University of California, Davis. "It's called an external parameter — the independent parameter in the [classic] equation of motion. So, time — the time we know since we learned to tell time on a clock — seems to disappear when you study physics, until you get to relativity.
Originally published on https://www.space.com
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(Saturday, April 20th, 2024)
"WHAT IS THE SLOWEST THING IN THE UNIVERSE??"
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A simulated image of NASA’s Nancy Grace Roman Space Telescope’s future observations toward the center of our galaxy, spanning less than 1 percent of the total area of Roman’s Galactic Bulge Time-Domain Survey. The simulated stars were drawn from the Besançon Galactic Model.
Exploring the Changing Universe with the Roman Space Telescope
The view from your backyard might paint the universe as an unchanging realm, where only twinkling stars and nearby objects, like satellites and meteors, stray from the apparent constancy. But stargazing through NASA’s upcoming Nancy Grace Roman Space Telescope will offer a front row seat to a dazzling display of cosmic fireworks sparkling across the sky.
Roman will view extremely faint infrared light, which has longer wavelengths than our eyes can see. Two of the mission’s core observing programs will monitor specific patches of the sky. Stitching the results together like stop-motion animation will create movies that reveal changing objects and fleeting events that would otherwise be hidden from our view.
Watch this video to learn about time-domain astronomy and how time will be a key element in NASA’s Nancy Grace Roman Space Telescope’s galactic bulge survey. Credit: NASA’s Goddard Space Flight Center
This type of science, called time-domain astronomy, is difficult for telescopes that have smaller views of space. Roman’s large field of view will help us see huge swaths of the universe. Instead of always looking at specific things and events astronomers have already identified, Roman will be able to repeatedly observe large areas of the sky to catch phenomena scientists can't predict. Then astronomers can find things no one knew were there!
One of Roman’s main surveys, the Galactic Bulge Time-Domain Survey, will monitor hundreds of millions of stars toward the center of our Milky Way galaxy. Astronomers will see many of the stars appear to flash or flicker over time.
This animation illustrates the concept of gravitational microlensing. When one star in the sky appears to pass nearly in front of another, the light rays of the background source star are bent due to the warped space-time around the foreground star. The closer star is then a virtual magnifying glass, amplifying the brightness of the background source star, so we refer to the foreground star as the lens star. If the lens star harbors a planetary system, then those planets can also act as lenses, each one producing a short change in the brightness of the source. Thus, we discover the presence of each exoplanet, and measure its mass and how far it is from its star. Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
That can happen when something like a star or planet moves in front of a background star from our point of view. Because anything with mass warps the fabric of space-time, light from the distant star bends around the nearer object as it passes by. That makes the nearer object act as a natural magnifying glass, creating a temporary spike in the brightness of the background star’s light. That signal lets astronomers know there’s an intervening object, even if they can’t see it directly.
This artist’s concept shows the region of the Milky Way NASA’s Nancy Grace Roman Space Telescope’s Galactic Bulge Time-Domain Survey will cover – relatively uncharted territory when it comes to planet-finding. That’s important because the way planets form and evolve may be different depending on where in the galaxy they’re located. Our solar system is situated near the outskirts of the Milky Way, about halfway out on one of the galaxy’s spiral arms. A recent Kepler Space Telescope study showed that stars on the fringes of the Milky Way possess fewer of the most common planet types that have been detected so far. Roman will search in the opposite direction, toward the center of the galaxy, and could find differences in that galactic neighborhood, too.
Using this method, called microlensing, Roman will likely set a new record for the farthest-known exoplanet. That would offer a glimpse of a different galactic neighborhood that could be home to worlds quite unlike the more than 5,500 that are currently known. Roman’s microlensing observations will also find starless planets, black holes, neutron stars, and more!
This animation shows a planet crossing in front of, or transiting, its host star and the corresponding light curve astronomers would see. Using this technique, scientists anticipate NASA’s Nancy Grace Roman Space Telescope could find 100,000 new worlds. Credit: NASA’s Goddard Space Flight Center/Chris Smith (USRA/GESTAR)
Stars Roman sees may also appear to flicker when a planet crosses in front of, or transits, its host star as it orbits. Roman could find 100,000 planets this way! Small icy objects that haunt the outskirts of our own solar system, known as Kuiper belt objects, may occasionally pass in front of faraway stars Roman sees, too. Astronomers will be able to see how much water the Kuiper belt objects have because the ice absorbs specific wavelengths of infrared light, providing a “fingerprint” of its presence. This will give us a window into our solar system’s early days.
This animation visualizes a type Ia supernova.
Roman’s High Latitude Time-Domain Survey will look beyond our galaxy to hunt for type Ia supernovas. These exploding stars originate from some binary star systems that contain at least one white dwarf – the small, hot core remnant of a Sun-like star. In some cases, the dwarf may siphon material from its companion. This triggers a runaway reaction that ultimately detonates the thief once it reaches a specific point where it has gained so much mass that it becomes unstable.
NASA’s upcoming Nancy Grace Roman Space Telescope will see thousands of exploding stars called supernovae across vast stretches of time and space. Using these observations, astronomers aim to shine a light on several cosmic mysteries, providing a window onto the universe’s distant past. Credit: NASA’s Goddard Space Flight Center
Since these rare explosions each peak at a similar, known intrinsic brightness, astronomers can use them to determine how far away they are by simply measuring how bright they appear. Astronomers will use Roman to study the light of these supernovas to find out how quickly they appear to be moving away from us.
By comparing how fast they’re receding at different distances, scientists can trace cosmic expansion over time. This will help us understand whether and how dark energy – the unexplained pressure thought to speed up the universe’s expansion – has changed throughout the history of the universe.
NASA’s Nancy Grace Roman Space Telescope will survey the same areas of the sky every few days. Researchers will mine this data to identify kilonovas – explosions that happen when two neutron stars or a neutron star and a black hole collide and merge. When these collisions happen, a fraction of the resulting debris is ejected as jets, which move near the speed of light. The remaining debris produces hot, glowing, neutron-rich clouds that forge heavy elements, like gold and platinum. Roman’s extensive data will help astronomers better identify how often these events occur, how much energy they give off, and how near or far they are.
And since this survey will repeatedly observe the same large vista of space, scientists will also see sporadic events like neutron stars colliding and stars being swept into black holes. Roman could even find new types of objects and events that astronomers have never seen before!
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