If you want to know what something in the universe works, all you need to do is understand that some measurable mass will give you the information you have to, and then lead you to the conclusion. Of course, there will be bias and errors and some other confounding factors here, and then they may lead you astray if you accidentally. So how to solve this problem? That is to do as much independent calculation as possible, and use as different technologies as possible to determine the natural data wealth as reliable as possible.
If you do everything right, each of your methods will bring you the same answer, then there is no ambiguity in this answer. If one measurement method or technique does not work, others will point you in the right direction. But when we try to apply these technologies in the ever-expanding universe, something confusing comes: we get one or two answers and they don't match each other. This is the greatest paradox in cosmology, and it may be the clue that uncovers the greatest mystery of our existence. Distance of galaxies near
—Redshift diagram. Because of the slight mismatch of the dynamic speed, this point is not completely on the line, which causes only a small deviation in all observed expansions. The first to reveal the expansion of the universe , the original data from the Hubble Telescope, all conforms to the small red box (Robert Kshner) in the lower left
Since 1920, we have known that the universe is expanding at a rate called the Hubble constant. From then on, generations have had a common pursuit, namely, to determine "what is the rate?" in
, there was only one type of technology: the cosmic distance ladder. The technique is very simple, with only four steps:
- selects a series of objects with known essential properties. When you measure some observable parts of them (such as the fluctuations in brightness over a period of time), you will know something inherent in them (such as the essence of its glowing).
- measures the number of observables, and then determines what its essential light is.
- then measure the obvious light and use the distance of the universe as you know it in an expanding universe to determine how far it is.
- Finally, measure the redshift of the object being explored
The further a galaxy is from us, the farther it expands from us, and the more its light is displayed on the redshift diagram. A galaxy moving with the ever-expanding universe will be several times longer than we are, even more than the year it takes for light to come from it to us today (doubled by the speed of light). But how fast the universe expands is impossible for astronomers using different technologies to reach an agreement. (View from Larry McNish of RASC Calgary Center)
redshift diagram connects everything together. Since the universe is expanding, any light passing through the universe will be lengthened. Remember, light is a wave with its special wavelength. Its wavelength determines its energy, and all atoms and particles in the universe have a special set of emission and absorption lines, which only appear at special wavelengths. If you can measure the wavelengths of these spectral lines that appear in nearby galaxies, you can determine how long the universe expands when it leaves that object from these light into your eyes
combines the distance between the spectral lines and various objects throughout the universe, even if the expansion rate changes over time, you can understand how fast the universe expands in different directions.
The history of the expansion of the universe includes its current scale. It is only by measuring how light redshifts as it passes through the expanded universe that it can understand it as it is, which requires a series of large independent measurements. (ESA ESA and Planck Association (main association) E. Siegel made corrections; NASA/Wikipedia daily user Lao Chen provided illustrations)
Throughout the 20th century, scientists used this technology to try and determine the history of our universe as much as possible. Cosmology - the discipline that studies what the universe is, where it comes from, how it evolves to the present, and what will be the future? - mainly comes from the pursuit of two parameters: the current expansion rate and the changes in the expansion rate of the universe over time.Until the 1990s, scientists were still unable to even determine the first parameter.
Scientists use the same technique but come up with different assumptions. Some teams use different types of celestial bodies from other teams to measure, while others make different measurement errors when using different instruments. There are a range of objects that prove to be more complex than we think. But many problems are still happening.
Standard candlelight method and standard ruler method are two different methods used by astronomers in the past to measure spatial expansion at different times/distances. Based on the changes in physical quantities such as photometry or angle size with distance, we can infer the history of universe expansion. If the universe expands too fast, there will not be enough time to form the earth. If we could find the oldest stars in our own galaxies, we knew the universe was at least as old as this one. If the expansion rate continues to evolve over time, because something important or radiation causes—or a different amount from the amount we determine—this will cause the expansion rate to change over time
Resolving these early debates was the primary scientific driving force for the manufacturing of the Hubble Space Telescope. Its core project is to make this measurement, and it has achieved great success. Its expansion rate is 72km/sec/mpc, and only 10% of uncertainty. This result was released in 2001, solving a long-standing controversial issue like Hubble's Law itself. In the discovery of dark matter and energy, it seems to give us a completely accurate and sustained picture of the universe.
Constructing the universe distance ladder includes galaxies from our solar system to other stars to nearby galaxies to distant distances. As each step comes, it brings its own uncertainty factors, especially the phase of changes in Cepheid and supernova ; if we live in a region of galaxies with lower density or too high, it will also cause too high or too low value estimates. There are enough independent methods to build cosmic distance ladders, and we no longer have reason to blame a "pedal" on the ladder for mismatching results due to different methods (NASA, ESA, A.FEILD (STSCL), and A.RIESS (STSCL/JHU)
At the time interval, the distance ladder group becomes increasingly complex. There are currently an incredible number of independent methods to measure the history of cosmic expansion.
- uses the distant gravitational lens html l5
- Use supernova data
- Use the rotation and dispersion characteristics of distant galaxies
- or use the surface brightness fluctuations of surface spirals
The results are the same. Whether you use Cephere variable star , RR Uranus or the red giant that is about to undergo helium fusion for calibration, you will get the same value: 73km/s/mps, the uncertainty is only 2-3%
RS of variable star Puppis, whose light reflects through interstellar clouds, has many kinds of variable stars, one of which is Cepheid variable stars, which can be measured both in our galaxies and 50 million in galaxies 60 million light-years away. This allows us to infer the distance from our own galaxies to galaxies farther in the universe. Other types of individual stars, such as the tip of AGB, such as the tip of AGB, or RR Lyrae variables, which can be used to replace Cepheid variable stars.
This would be a huge smooth cosmology, except for one problem. It's 2019 now, and there is a second way to measure the expansion rate of the universe. Instead of observing distant objects, we can measure how their light evolves. When we do this, we get a value of about 67km/s/mpc, which claims to be only 1-2%, these numbers differ by nine percent, and their uncertainties do not overlap.
Modern methods of measuring tension from distance ladder (red) using early signal data from CMB and BAO, there is a contradiction in the way of measuring tension from distance ladder (red).It is very likely that early signal errors were correct and the distance ladder had fundamental problems; it is possible that small-scale errors deviate the early signal methods, while the distance ladder was correct; it is also possible that both are correct and some new forms of physics (displayed at the beginning of the article) are the culprit. But for now, we are not sure. (ADAM RIESS) (Private Communication)
No matter what, this time, things are different. We can no longer expect that one group is right or wrong. Nor can we expect the conclusion to be between the two, and both groups create some kind of error in their assumptions. The reason we can't rely on these is that there is too much independent evidence. If we try to explain a measure with a wrong one, it will conflict with other measures that have been derived.
The total amount of matter in the universe is the determinant of how the universe expands over time. Einstein's general theory of relativity connects the internal energy of the universe with the overall curvature. If the universe expands too fast, it implies that there is less matter and more dark matter in the universe, which will conflict with the observations
Before Planck, the best one showed a Hubble parameter about 71km/s/mpc, but now a value equal to 69 is too great for the dark matter density we observe through other ways and the scalar spectral index (y-axis right axis), and we need to find meaning through the large-scale structure of the universe. (P.A.R.ADE and AL. and Planck Institute) (2015)
For example, from the large-scale structure of the universe, the density of galaxies and many other sources, we know that the total amount of matter in the universe should be 30% of the critical density. We also see that scalar spectral index—a telling us how gravity forms a bonding structure on small and large scales—will be slightly smaller than 1.
If the expansion rate is too high, you will not only get a universe with very little matter and high critical density compared to our universe, but you will also get a universe that is too young: it has only experienced 12.5 billion years rather than 13.8 billion years. Since we live in a galaxy with stars identified over 13 billion years, this creates a huge problem: these problems cannot be coordinated.
is located in the Milky Way 4140 light years away. SDSS J102915+172927 is an ancient star with only heavy elements of 1/20000th of the sun. It should be over 13 billion years old: it is one of the oldest stars in the universe, and was even born before the Milky Way. Stars like this remind us that the universe cannot be younger than such stars (ESO, Data-based Space Search 2)
but maybe no one is wrong. Perhaps the early artifacts point to a set of true facts about the universe:
- it is 13.8 billion years old,
- it is roughly 70%/25%/5%/ dark energy /dark matter/ordinary matter,
- it does look consistent with the expansion rate of 67km/s/mpc on the lesser end.
And perhaps the distance ladder also points out a series of truths about the universe.
Even if this sounds weird, both groups are probably right. The reason for the compromise comes from the third reason most people are not willing to consider at the moment. Apart from the wrong distance ladder group or the wrong early ruin group, perhaps our assumptions about physics and the laws of nature in the universe are wrong. In other words, we may not be resolving this contradiction, maybe what we see is a clue about new physics.
A double-lens quasar , as shown in the figure, is caused by a gravitational lens. If multiple time-lapse images can be understood, it is possible to reconstruct the expansion rate of the universe based on the quasar we are discussing. The earliest results show the entire quadrilateral quasar system. It is possible that the way we measure the expansion rate of the universe actually shows something completely new in the nature of the universe. (NASA Hubble Space Telescope, TOMMASO TREU/UCLA and BIRRER ET AL)
It is possible that the way we measure the expansion rate of the universe actually shows something completely new in the nature of the universe.Something that changes over time will become another technique of these two different classes of technology that can succumb to the explanation of the historical conclusions of the expansion of the universe. Some choices are included here:
- The local areas of our universe have something unusual (not yet agreed upon)
- dark energy is making unpredictable changes over time. The performance of gravity of
- is different from the predictions we made from cosmological perspective
- or there is now a completely new field or force permeates the universe
The possibility of evolving dark energy is particularly interesting and important, because this is NASA's future flagship mission in astrophysics WFIRST, which is clearly designed to measure. The observation area of the Hubble Telescope (top left) is compared with the area that WFIRST can observe at the same depth and in the same time. WFIRAT's wide-area vision will allow us to capture more distant supernova images than before and allow us to conduct in-depth and extensive investigations of galaxies at cosmic scales that have never been detected before. No matter what it discovers, it will bring about a scientific revolution. (NASA/GODDARD/WFIRST)
Currently, we claim that dark energy and cosmic constant are consistent. This means that while the universe expands, the density of dark energy remains consistent, rather than getting lower (like matter) dark energy can also increase over time at the same time, or it changes its behavior: pushing space inward or outward to varying degrees.
Today, in a world without WFIRST, our best limit on this is about 10% level to show that dark energy is consistent with cosmic constants. With WFIRST, we will be able to measure any deviation to a level of 1%: this is enough to test whether evolving dark energy can solve the controversy over the expansion of the universe. All we can do before we find the answer is to continue to refine our best measurements and find clues to solve the problem from a complete set of evidence.
When the radiation density of matter (including ordinary matter and dark matter) decreases due to the increase in volume of the universe, dark matter is an energy form inherent in space. When new space is born in the expanding universe, the density of dark matter remains the same. If dark energy changes over time, we will not only find possible explanations about the puzzle of cosmic expansion, but also revolutionary new perspectives about the nature of existence. (E.SIEGEL/Outside the galaxy)
This is not some edge idea, there are some scientists who are going upstream that are overemphasizing the slight differences in data. If both of these views are correct and no one can spot the flaws of either, this may be the first clue to our next big step in understanding the universe. Nobel Prize winner Adam Rees, perhaps the most famous figure currently studying the Ushidala. He kindly recorded a podcast with me about what these ideas mean for the future of the universe.
Author: Ethan Siegel
FY: Zhihai
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