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There is a large suite of scientific evidence supporting the image of the expanding Universe and the Big Bang. The small number of input parameters and the large number of successes and predictions observed subsequently are among the features of a successful scientific theory.NASA / GSFC
What are the rules governing reality? If you can determine the laws of nature, you can successfully predict the outcome of any experiment. You can create any physical configuration you have imagined and you will know how it will behave as you move forward. Even in the parameters of quantum mechanics, you could give an exact probability distribution, the reality corresponding to what you would observe on many occasions.
It's the dream of any scientist who works with a theory: to propose something so successful that his predictive and post-dicative powers are correct every time. In 2018, we are closer than ever to making every effort. But there are rules to theorize successfully, and if you violate them, your theory will not only be wrong; it will be a bad science.
One of the great riddles of the 1500s was the way the planets were evolving in an apparently retrograde way. This could be explained either by the geocentric model of Ptolemy (L) or by the Heliocentric model of Copernicus (R). However, the right to arbitrary precision of details was something that no one could do. As interesting as these two models are, no one would have much to say if another new planet had been discovered. Our theories must strive to be not only descriptive but also normative.Ethan Siegel / Beyond the galaxy
Whenever we observe a phenomenon occurring in the universe, our curiosity compels us to try to understand what is causing it. It is not enough to describe it with a poetic image or an analogy; we demand a quantitative description of what happens, when and by what amount. We seek to understand which processes determine this phenomenon and how these processes create the observed effect of the exact magnitude observed.
And we want to be able to apply our rules to systems that we have not yet observed or measured, to predict new behavior that would not occur in other formulations. Ideas are shoveled, but good ideas are extremely rare. The simple reason why? Most ideas assume too much and predict too little. There is a science of how it all works.
Hubble's discovery of a Cepheid variable in the Andromeda galaxy, M31, opened the Universe, giving us the necessary observational evidence for galaxies beyond the Milky Way. and leading to the expanding Universe.E. Hubble, NASA, ESA, R. Gendler, Z. Levay and the Hubble Heritage Team
Take the expanding Universe, for example. When we observe galaxies outside the Milky Way, we can measure individual stars within them. Since we measure the stars in our own galaxy and we believe (with great precision) that we understand how stars work, when we measure the same types of stars elsewhere, we can use this information to determine their distance. . Get enough of these measurements for the right types of stars, and you can deduce how far away these galaxies are.
The further a galaxy is, the farther away it is from us, and the more its light appears redecorated. A galaxy moving with the expanding Universe will have an even higher number of light years, today, than the number of years (multiplied by the speed of light) that It took the light emitted to reach us.Larry McNish of RASC Calgary Center
Add to that the fact that light seems to come down from these galaxies, and we can deduce one of two things:
- the distant galaxies move away from us, and their light appears redder because of their movement relative to us,
- or the space between these galaxies and ourselves is expanding, so that the wavelength of this light lengthens and becomes redder throughout its course.
Either or both would be in accordance with the known laws of physics, which would make excellent explanations. When we examine the distance-redshift relationship for neighboring galaxies, we can see that it does not distinguish between these two possibilities.
The redshift-distance relationship for distant galaxies. The points that do not fall exactly to the right have the slight shift to the particular speed differences, which offer only slight deviations from the overall observed expansion. The original data of Edwin Hubble, used for the first time to show that the Universe was expanding, all fit in the little red box at the bottom left.Robert Kirshner, PNAS, 101, 1, 8-13 (2004)
This is a reasonable way to start theorizing! See a phenomenon and offer a plausible explanation (or multiple plausible explanations) for what you have observed. These two ideas, however, would have consequences for the Universe. If distant galaxies were moving away from us, then you would reach a point where you are limited by the speed of light: the ultimate speed limit of the Universe.
But if the space between the galaxies was expanding, there is no limit to the amount of redshift we could observe. At a great distance, we would see a difference between these two explanations. Aside from all the biases, if you can make a physical prediction based on your theory that is unique and powerful, then testing it will be the deciding factor.
Differences between a motion-only explanation for offsets / distances (dashed line) and predictions (solid) of general relativity for distances in the expanding universe. In the end, only GR predictions correspond to what we observe.Wikimedia Commons Redshiftimprove User
The fact that we can use a theory to make a unique and powerful prediction is one of the characteristics of what separates a good scientific theory from the bad one. If your theory does not make a prediction, it is rather useless with regard to physics. This is an accusation often properly posed against string theory, whose predictions are virtually unworkable in practice.
But when the charge is directed against cosmic inflation, it's completely unfair. Inflation has made no less than six unique predictions that have not been tested when it was proposed, and four of which have already been validated, with the other two waiting for better experiments to test them. Your theory, to be of any quality, must be tested against alternatives.
CMB fluctuations, formation and correlations between large-scale structure and modern observations of gravitational lenses, among others, all point to the same thing: an accelerated universe, containing and full of dark matter and dark energy. But alternatives that offer different observable forecasts must also be taken into account.Chris Blake and Sam Moorfield
It must not be unnecessarily complicated. There are many mysteries in the Universe today, small scale phenomena like why neutrinos have mass to dark matter and dark energy on a large scale. There are a multitude of models to explain these riddles (and others), but most of the theoretical ideas are rather bad.
Why?
Because most of them invoke a whole series of physical news to explain a single otherwise inexplicable observation.
Although the energy densities of matter, radiation, and dark energy are well known, there is still plenty of room for maneuver in the equation of state of the art. Dark energy. This could be a constant, but it could also increase or decrease over time.Quantum stories
Take dark energy for example. At the present time, it is quite explicable by adding a new parameter – a cosmological constant – to our best-known theory of gravity, general relativity. But there are other explanations that could also do the trick.
- Dark energy can be a new field, with a non-constant state equation and / or an amplitude that changes with time.
- It can be linked to inflation via a quintessential type field.
- Or general relativity could be replaced by any alternative we might find that is not already excluded by existing data.
These explanations are all important to keep in mind as possibilities, but they are also examples of a speculative scientific theory that no one should believe.
In itself, Planck data do not provide very strict constraints on the state of the dark energy equation. But when we associate it with the full suite of large – scale structure data (BAO) and available supernova datasets, we can demonstrate that black energy is extremely consistent be a pure cosmological constant (at the intersection of the two dotted lines). No motivation exists for other alternatives with additional free parameters.Planck 2018 results. VI. Cosmological parameters; Planck Collaboration (2018)
Why not? Because these alternative explanations do nothing better than the default, the explanation "vanilla" of a cosmological constant. The complete set of data we have on the behavior of dark energy – including supernovae, gamma ray bursts, baryonic acoustic oscillations, cosmic microwave background and large-scale cluster data – does not show any of these data .
There are no puzzles or unresolved issues with the standard view of dark energy. In other words, there is no motivation to complicate things unnecessarily. Like Russell's teapot, the mere fact that something is not excluded does not mean it's worth considering.
The cluster of galaxies colliding "El Gordo", the largest of the observable universe, shows the same evidence of dark matter that other clusters collide. It is possible to explain El Gordo with new physics, but it is a useless complication. standard collisionless dark matter is doing well here.NASA, ESA, J. Jee (University of California, Davis), J. Hughes (Rutgers University), F. Menanteau (Rutgers University and University of Illinois, Urbana-Champaign), C. Sifon (Leiden Obs. ), R. Mandelbum (Carnegie Mellon University), L. Barrientos (Catolic University of Chile) and K. Ng (University of California, Davis)
The burden of proof rests with any theorist to show that his new model has a convincing motivation. Historically, this motivation has taken the form of unexplained data, which require explanations and can not be explained without new physics. If this can be explained without new physics, that's the way to go. History has shown that this path is almost always correct.
If you can explain what your standard theory does not explain, with a new field, a new particle or a new interaction, that's the next path you should try. Ideally, you will explain several observations with this new parameter of your theory, and this will lead you to new predictions that you can test.
A dark energy universe (red), a high energy universe of inhomogeneity (blue) and a critical universe, without black energy (green). Note that the blue line behaves differently from dark energy. New ideas must make different and observable predictions of other leading ideas.Gábor Rácz et al., 2017
But adding more and more changes to your theory – making your model objectively more complicated – will of course have the power to give you a better fit to the data. In general, the number of new free parameters introduced by your idea must be much smaller than the number of new elements it is supposed to explain. The great power of science lies in its ability to predict and explain what we see in the universe. The essential thing is to do it as simply as possible, but not to simplify it further.
Bad scientific theories abound, overflowing with unnecessary complications, extra sets of parameters, and unmotivated and misguided speculation. Unless there is a reality check, in the form of experimental data or observation, it's not worth wasting your time.
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There is a large suite of scientific evidence supporting the image of the expanding Universe and the Big Bang. The small number of input parameters and the large number of successes and predictions observed subsequently are among the features of a successful scientific theory.NASA / GSFC
What are the rules governing reality? If you can determine the laws of nature, you can successfully predict the outcome of any experiment. You can create any physical configuration you have imagined and you will know how it will behave as you move forward. Even in the parameters of quantum mechanics, you could give an exact probability distribution, the reality corresponding to what you would observe on many occasions.
It's the dream of any scientist who works with a theory: to propose something so successful that his predictive and post-dicative powers are correct every time. In 2018, we are closer than ever to making every effort. But there are rules to theorize successfully, and if you violate them, your theory will not only be wrong; it will be a bad science.
One of the great riddles of the 1500s was the way the planets were evolving in an apparently retrograde way. This could be explained either by the geocentric model of Ptolemy (L) or by the Heliocentric model of Copernicus (R). However, the right to arbitrary precision of details was something that no one could do. As interesting as these two models are, no one would have much to say if another new planet had been discovered. Our theories must strive to be not only descriptive but also normative.Ethan Siegel / Beyond the galaxy
Whenever we observe a phenomenon occurring in the universe, our curiosity compels us to try to understand what is causing it. It is not enough to describe it with a poetic image or an analogy; we demand a quantitative description of what happens, when and by what amount. We seek to understand which processes determine this phenomenon and how these processes create the observed effect of the exact magnitude observed.
And we want to be able to apply our rules to systems that we have not yet observed or measured, to predict new behavior that would not occur in other formulations. Ideas are shoveled, but good ideas are extremely rare. The simple reason why? Most ideas assume too much and predict too little. There is a science of how it all works.
Hubble's discovery of a Cepheid variable in the Andromeda galaxy, M31, opened the Universe, giving us the necessary observational evidence for galaxies beyond the Milky Way. and leading to the expanding Universe.E. Hubble, NASA, ESA, R. Gendler, Z. Levay and the Hubble Heritage Team
Take the expanding Universe, for example. When we observe galaxies outside the Milky Way, we can measure individual stars within them. Since we measure the stars in our own galaxy and we believe (with great precision) that we understand how stars work, when we measure the same types of stars elsewhere, we can use this information to determine their distance. . Get enough of these measurements for the right types of stars, and you can deduce how far away these galaxies are.
The further a galaxy is, the farther away it is from us, and the more its light appears redecorated. A galaxy moving with the expanding Universe will have an even higher number of light years, today, than the number of years (multiplied by the speed of light) that It took the light emitted to reach us.Larry McNish of RASC Calgary Center
Add to that the fact that light seems to come down from these galaxies, and we can deduce one of two things:
- the distant galaxies move away from us, and their light appears redder because of their movement relative to us,
- or the space between these galaxies and ourselves is expanding, so that the wavelength of this light lengthens and becomes redder throughout its course.
Either or both would be in accordance with the known laws of physics, which would make excellent explanations. When we examine the distance-redshift relationship for neighboring galaxies, we can see that it does not distinguish between these two possibilities.
The redshift-distance relationship for distant galaxies. The points that do not fall exactly to the right have the slight shift to the particular speed differences, which offer only slight deviations from the overall observed expansion. The original data of Edwin Hubble, used for the first time to show that the Universe was expanding, all fit in the little red box at the bottom left.Robert Kirshner, PNAS, 101, 1, 8-13 (2004)
This is a reasonable way to start theorizing! See a phenomenon and offer a plausible explanation (or multiple plausible explanations) for what you have observed. These two ideas, however, would have consequences for the Universe. If distant galaxies were moving away from us, then you would reach a point where you are limited by the speed of light: the ultimate speed limit of the Universe.
But if the space between the galaxies was expanding, there is no limit to the amount of redshift we could observe. At a great distance, we would see a difference between these two explanations. Aside from all the biases, if you can make a physical prediction based on your theory that is unique and powerful, then testing it will be the deciding factor.
Differences between a motion-only explanation for offsets / distances (dashed line) and predictions (solid) of general relativity for distances in the expanding universe. In the end, only GR predictions correspond to what we observe.Wikimedia Commons Redshiftimprove User
The fact that we can use a theory to make a unique and powerful prediction is one of the characteristics of what separates a good scientific theory from the bad one. If your theory does not make a prediction, it is rather useless with regard to physics. This is an accusation often properly posed against string theory, whose predictions are virtually unworkable in practice.
But when the charge is directed against cosmic inflation, it's completely unfair. Inflation has made no less than six unique predictions that have not been tested when it was proposed, and four of which have already been validated, with the other two waiting for better experiments to test them. Your theory, to be of any quality, must be tested against alternatives.
CMB fluctuations, formation and correlations between large-scale structure and modern observations of gravitational lenses, among others, all point to the same thing: an accelerated universe, containing and full of dark matter and dark energy. But alternatives that offer different observable forecasts must also be taken into account.Chris Blake and Sam Moorfield
It must not be unnecessarily complicated. There are many mysteries in the Universe today, small scale phenomena like why neutrinos have mass to dark matter and dark energy on a large scale. There are a multitude of models to explain these riddles (and others), but most of the theoretical ideas are rather bad.
Why?
Because most of them invoke a whole series of physical news to explain a single otherwise inexplicable observation.
Although the energy densities of matter, radiation, and dark energy are well known, there is still plenty of room for maneuver in the equation of state of the art. Dark energy. This could be a constant, but it could also increase or decrease over time.Quantum stories
Take dark energy for example. At the present time, it is quite explicable by adding a new parameter – a cosmological constant – to our best-known theory of gravity, general relativity. But there are other explanations that could also do the trick.
- Dark energy can be a new field, with a non-constant state equation and / or an amplitude that changes with time.
- It can be linked to inflation via a quintessential type field.
- Or general relativity could be replaced by any alternative we might find that is not already excluded by existing data.
These explanations are all important to keep in mind as possibilities, but they are also examples of a speculative scientific theory that no one should believe.
In itself, Planck data do not provide very strict constraints on the state of the dark energy equation. But when we associate it with the full suite of large – scale structure data (BAO) and available supernova datasets, we can demonstrate that black energy is extremely consistent be a pure cosmological constant (at the intersection of the two dotted lines). No motivation exists for other alternatives with additional free parameters.Planck 2018 results. VI. Cosmological parameters; Planck Collaboration (2018)
Why not? Because these alternative explanations do nothing better than the default, the explanation "vanilla" of a cosmological constant. The complete set of data we have on the behavior of dark energy – including supernovae, gamma ray bursts, baryonic acoustic oscillations, cosmic microwave background and large-scale cluster data – does not show any of these data .
There are no puzzles or unresolved issues with the standard view of dark energy. In other words, there is no motivation to complicate things unnecessarily. Like Russell's teapot, the mere fact that something is not excluded does not mean it's worth considering.
The cluster of galaxies colliding "El Gordo", the largest of the observable universe, shows the same evidence of dark matter that other clusters collide. It is possible to explain El Gordo with new physics, but it is a useless complication. standard collisionless dark matter is doing well here.NASA, ESA, J. Jee (University of California, Davis), J. Hughes (Rutgers University), F. Menanteau (Rutgers University and University of Illinois, Urbana-Champaign), C. Sifon (Leiden Obs. ), R. Mandelbum (Carnegie Mellon University), L. Barrientos (Catolic University of Chile) and K. Ng (University of California, Davis)
The burden of proof rests with any theorist to show that his new model has a convincing motivation. Historically, this motivation has taken the form of unexplained data, which require explanations and can not be explained without new physics. If this can be explained without new physics, that's the way to go. History has shown that this path is almost always correct.
If you can explain what your standard theory does not explain, with a new field, a new particle or a new interaction, that's the next path you should try. Ideally, you will explain several observations with this new parameter of your theory, and this will lead you to new predictions that you can test.
A dark energy universe (red), a high energy universe of inhomogeneity (blue) and a critical universe, without black energy (green). Note that the blue line behaves differently from dark energy. New ideas must make different and observable predictions of other leading ideas.Gábor Rácz et al., 2017
But adding more and more changes to your theory – making your model objectively more complicated – will of course have the power to give you a better fit to the data. In general, the number of new free parameters introduced by your idea must be much smaller than the number of new elements it is supposed to explain. The great power of science lies in its ability to predict and explain what we see in the universe. The essential thing is to do it as simply as possible, but not to simplify it further.
Bad scientific theories abound, overflowing with unnecessary complications, extra sets of parameters, and unmotivated and misguided speculation. Unless there is a reality check, in the form of experimental data or observation, it's not worth wasting your time.
