Astronomy Answers
AstronomyAnswerBook: Science

[Astronomy Answers] [Dictionary] [AnswerBook] [Universe Family Tree] [Science] [Starry Sky] [Planet Positions] [Calculate] [Colophon]

1. The Use of Space Research ... 2. The Cost of Space Research ... 3. Predicting ... 4. How Far has Science Come? ... 5. Systems of Units ... 6. Natural Units ... 7. Scientific Astronomical Articles and Data ... 8. So you think you have an explanation for nearly everything? ... 9. Generate Scientific Interest for your Theory

This page answers questions about science. The questions are:

What science is and how it works is explained on the separate Science Page.


1. The Use of Space Research

It is not easy to determine which things are useful and which are not. Something that you think is very useful may be useless to someone else. Is something already useful if you enjoy it?

Much space research just tries to learn more about the things in space, without having a clear idea beforehand about the usefulness of the new knowledge for humanity. Just like in any other research, you don't know beforehand what things will be discovered, and it happens often that one finds useful things or knowledge that was totally unexpected. Also, it is quite a challenge to design, build, and lauch a satellite and its instruments, and to draw conclusions from the enormous number of raw measurements that the instruments yield, and the experience and skills that you gain in doing that can be usefully applied for earthly tasks as well, where they may be of more obvious use to humankind. I don't think it is a coincidence that the countries where the most scientific research is done tend to be the most prosperous ones.

Because we researched things in space, we now know that there are things in space that can cause trouble for us on Earth, such as solar flares that can disable satellites and electricity grids, and such as meteorites that can hit the Earth and cause terrible destruction. If we hadn't started investigating the Sun and meteorites and the Solar System, then we would not have known about these dangers. If we learn enough about them, then we may be able to predict them and perhaps even do something about them, or at least limit the damage that they can do.

Thanks to research of the Sun and the stars, we now know that the Sun will continue to shine much as it does today for about another five thousand million years, so we don't need to worry that the Sun will run out of fuel soon. This knowledge is not something that you can read from some gauge, but required many different things to be discovered and researched; things that were not researched with the age of the Sun in mind, but after all of those other things had been researched, someone suddenly realized that you could use the results to estimate how much time the Sun has left.


2. The Cost of Space Research

How expensive it is to design, build, and launch a space probe depends on what kind of equipment and instruments you put inside and how far it has to travel and what it is supposed to do. I'd say you can't do very much for less than a few million euros. Here is a list of estimated cost of a number of recent and older space missions, converted to millions of euros (at $1 ≈ €1 and £1 ≈ €1,5):

Table 1: Space Mission Costs

Mission Goal Cost
Cassini Saturn 2700
Galileo Jupiter 1600
Beagle Mars 60
Voyager Jupiter, Saturn, Uranus, Neptune 865
Clementine the Moon, asteroid 98
NEAR two asteroids 221
Mars Pathfinder Mars 265
Lunar Prospector the Moon 61
Deep Space 1 Mars, asteroid, comet 95
Stardust comet 200
Hubble Space Telescope telescope around the Earth 3800 through 1999
International Space Station space station around the Earth at least 100,000
Mir space station around the Earth 4300
SIRTF infrared telescope around the Earth 450

(For example, see−1.html.)

As you can tell, the International Space Station (ISS) is by far the most expensive. For that amount of money, you could send at least 400 rovers to Mars or 30 space probes to Saturn. I'd prefer to spend the money that now goes to the ISS on such unmanned space missions instead.


3. Predicting

Predicting is very important in science. Only by predicting things and then looking if they actually happen as predicted can you find out if your prediction method really works. If you understand something very well, then you should be able to predict how it is going to work, so if you can predict something very well (and often), then perhaps you really do understand it.

If you don't know whether something works by method A or by method B, then you can use both methods to make predictions, and then you can check which predictions fail to come true. A method whose predictions are usually wrong is not a good one.


4. How Far has Science Come?

This question can be interpreted in at least two ways. I could take it to be "how many things do we know about all things?", but science investigates millions of different things and nobody could say how far science is for each of those things. A complete answer would be longer than an encyclopedia.

I could also take the question to be "do we know just about everything that there is to know?". The answer to that question is very clearly "No". It doesn't matter which subject you choose, you can always ask more questions about it. And I think that every scientist will agree that the more you discover about a subject, the more you find out that there are many things you don't yet know about it. Generally speaking, only people who know very little about something think that they know everything about it.

5. Systems of Units

When you measure something, then you compare it to some standard. When we say that a house is 20 meters long, then we mean that it is 20 times as long as a standard length that we call the meter. A measurement such as "20 meters" is made up from a magnitude (here 20) and a unit (here "meter").

One can measure lengths with many other units as well, such as kilometers or centimeters (relatives of the meter), or inches, feet, or miles, but all of those units of length can be easily transformed into one another by multiplying them by some number that is fixed for each kind of transformation. For example, to get from meters to kilometers, just divide the magnitude by 1000. And to get from inches to centimeters, just multiply the magnitude by 2.54.

All units of length are essentially equivalent, so it is just an accident of history which particular units we use, except that we tend to use units that are about as large as the thing that we're trying to measure, because otherwise you get numbers that are very large or very small. For example, the length of the house mentioned above is also equal to 0.000 000 000 000 0021 lightyears, but it's unpleasant to calculate with all of those zeros after the decimal point, so it is much more convenient to refer to that length as 20 meters. Conversely, the nearest star (other than the Sun) is at about 41 000 000 000 000 000 meters from us, but that is not a very convenient number, either, so we prefer to refer to that distance as 4.3 lightyears.

There are also things that you cannot compare to a meter, such as how long something lasts, or how hard you push against something, or how fast something moves, or how brightly something shines. To measure such things, you need different units that themselves cannot be compared to a meter, such as the second or the kilometer per hour.

Scientists have discovered that you can describe all measurements using just seven units and (dimensionless) numbers, if those seven units are sufficiently independent from one another (so that you cannot calculate one of those units from some combination of the other six). A collection of independent units is called a system of units. It doesn't matter exactly which units are part of such a system, as long as they are independent of one another.

The International System of Units (the SI) is based on the following fundamental units:

Table 2: SI-units

Dimension Unit
Name Symbol
length meter m
time second s
mass kilogram kg
electrical current ampere A
thermodynamical temperature kelvin K
intensity of light candela cd
amount of matter mole mol

You cannot express any of these fundamental units as some combination of the others, so they are independent of one another. You can combine fundamental units and make derivative units out of them. For example, if you divide a length by a time then you get a speed, so if you divide a unit of length by a unit of time then you get a unit of speed, such as the meter per second (m/s). And you get a surface area by multiplying a length by another length, so you get a unit of surface area by multiplying a unit of length by itself, for example the square meter (m²).

It doesn't matter exactly which units are in a system of units, as long as they are independent of one another. For example, it is fine to use the mile instead of the meter, and the pound instead of the kilogram (but most scientists, and most countries other than the USA and Great Britain, use the SI units). You can also use a system of units that has fewer than seven units, but then you cannot use that system of units to describe certain measurements. For example, one can define a "cgs" system of units that uses the centimeter (instead of the meter), the gram (instead of the kilogram), and the second, but that system cannot be used to measure electrical currents.

It is even possible to use units that are not (fractional) multiples of the SI units. You could, for instance, define a system of units that is the same as the SI except that it uses not length but speed as a fundamental dimension, with a corresponding unit that is called the "flup". Then the greatest speed that a particular car can reach is no longer 200 kilometers per hour (or 124 miles per hour), but (for example) 85 flup, and then the length is a derived dimension, equal to the product of a speed and a time, which is then measured in flup-seconds.


6. Natural Units

Because the common systems of units are rather arbitrary, people have sought for systems of units that are tied to fundamental constants of nature.

Using a system of units in which the speed of light in a vacuum is unity is fairly common in those branches of physics where speeds close to that of light occur. In fact, such systems commonly set some other fundamental physical constants to unity as well, such as the universal constant of gravity (usually denoted G) and the reduced Planck constant (usually denoted ℏ, which is a "h" with a horizontal bar through it). These systems are referred to as systems of "Natural Units".

Many formulas in physics contain fundamental physical constants, so if one can set those constants to unity (by making an appropriate choice of units), then the formulas look simpler. For example, the formula for the Schwarzschild radius of a spherical black hole is

\begin{equation} r = \frac{2 G M}{c^2} \end{equation}

where \(r\) is the radius, \(G\) is the universal constant of gravity, \(M\) is the mass, and \(c\) is the speed of light in a vacuum. If we use a system of units where \(G\) and \(c\) are set to unity, then the formula simplifies to

\begin{equation} r = 2 M \end{equation}

This implies that mass and length can be measured (in this system of units) in the same units, just like the time.

Of course, one cannot set all fundamental constants to unity, because they are not all independent of one another. Because there can be at most seven independent units in a system of units, at most seven independent constants of nature can be defined equal to 1 (which completely fixes the whole system of units).

See, e.g., for more information about natural units.


7. Scientific Astronomical Articles and Data

Good sources of astronomical scientific articles are:

The first source gives access to abstracts (summaries) of a great number of astronomical articles. Most astronomical scientific journals are extremely expensive, but some journals let their articles be scanned when they are a few years old, and then you can read those scanned articles for free through ADS. Many old articles (such as some by Edwin Hubble) can be read for free through ADS.

The second source gives access to preprints, which are preliminary version of scientific articles that are distributed to get comments from colleagues that can be incorporated into the final official version. Preprints have much less status than the later official articles that are based on them, because preprints need not be completely finished and haven't been through the peer review process of the journal yet. For this reason, they are more often available for free. You may therefore be able to find preprints of recent articles or of articles that will probably not become available for free any time soon. ADS has begun referring to preprints as well.

Many scientific data sets about astronomical things are available from VizieR: Nowadays many astronomical articles have associated data sets, which can be found at VizieR through ADS, even if the full articles themselves are not (yet) freely accessible.


8. So you think you have an explanation for nearly everything?

It happens more often that someone has an idea for an explanation of nearly everything. Unfortunately, it is a lot easier to get such an idea than it is to prove that that idea says something useful about us, the world, and the Universe.

Many people think that it is enough to show with a few sentences that their explanation might be the correct one, but that is not enough for scientists. In de Middle Ages things did work that way: "My brother got ill the night after the neighbor did a weird dance. The neighbor must be a witch who made my brother ill with her magic dance!" Yes, it might be that witches exist and that the neighbor is such a witch and that she can do magic dances and that she made your brother ill using such a dance, but that is not proof that all of that is true. It might also be that witches do not exist and that your neighbor had nothing to do with the illness of your brother and that your brother actually got ill from some germs that got on his hands when he picked up a stone from the street and he forgot to wash his hands before dinner. And there are surely plenty more logical explanations that are quite different again.

Different people can have very different explanations for the same things in the world. All of those explanations can be very logical, but still only one of them can be the correct one ― and maybe none of them is the correct one. To be able to tell which explanation is the correct one you must be able to measure something related to it, and you must be able to predict from your explanation what the outcome of that measurement should be if your explanation is the correct one. If those predictions are different for different possible explanations, then you can tell from the outcome of the measurements which explanation fits the outcomes the best. If you cannot measure anything related to your explanation, then scientists usually don't find it interesting, because then you cannot test if it is correct. Then it can only lead to an endless yes/no argument.

Regarding paranormal things: There is no convincing scientific proof for paranormal things, though many so-called paranormal things have been tested scientifically. Always the paranormal effect turned out not to exist ― or at least not to occur during the scientific test.

Regarding faith: Scientists don't see faith as proof of truth, because different people can believe conflicting things, and those cannot all be true at the same time. If your explanation takes belief as proof of truth, and assumes that paranormal effects are true, then it is not likely that there will be much scientific interest in it.

It is good to think about the world and to want to know how everything works. I think that is how everyone began who later turned into a scientist ― I did. Very many people have thought about the world and the Universe, and they have had many strange ideas, and some of those ideas turned out to be correct but very many of them turned out not to be correct. If your idea turns out not to be correct then that does not mean that you are dumb, but that the world is different from what you thought ― and that is no fault of yours. The world is incredibly complicated, but that makes it so interesting to study it.


9. Generate Scientific Interest for your Theory

Suppose that you have invented a model or theory that you think describes some astronomical phenomenon better than all other theories do, or you think you have proof that an established scientific law or theory is wrong. How can you get scientists to be interested in your work?

The way in which scientists try to get their work noticed by other scientists is by publishing that work, preferably in a leading scientific journal. The most prestigious journals let other scientists review the submitted article, and those reviewers give their opinion about the quality of the work. They might seek answers to questions like the following: Are the conclusions based on logical arguments, and are they supported by the discussed observations or calculations? Are the used methods applied in the correct fashion? Is a reasonable description given of how the conclusions of the article relate to other (recent) work in the same field of knowledge? If the review is positive, and if the editor of the journal thinks that the article is interesting enough for that journal, then the article is published. If the review is not positive enough, but the reviewer thinks that with some improvements it can be good enough, then the author usually is given the opportunity to improve the article and submit it again for publication.

Most of these journals ask you to pay a considerable amount of money to get your paper published, and taking a subscription to the journal is usually not cheap, eithr. Most scientists are supported by their employer in that regard: the employer pays for publishing, and pays for the subscription to the journal.

This means that it isn't so easy for an average person who is not a professional scientist to get papers published in such journals. Some persistent people may then try to bring their work to the attention of a scientist that they can contact somehow. Their hope is that if they can convince the scientist that they are right, then maybe that scientist will help to get the work published.

However, it is usually even harder for a lay person to convince a scientist than it is for a scientist to convince other scientists, because the lay person usually has much less experience in using the scientific methods and in writing a good article of which it is easy to tell that it has no big holes in it.

The most important thing that you should do to convince a scientist that your theory is better than the usual theory is to show that your theory gives results that are more accurate (compared to the observations) than the usual theory. It is not sufficient to give logical arguments why your theory is better than the other one, because maybe your assumptions are incorrect, and then the conclusions based on those assumptions are incorrect, too, even if the conclusions follow logically and without error from those assumptions. Proving that your assumptions are correct is at least as tough as proving that your conclusions follow logically from the assumptions.

The only efficient manner to show that your theory is valuable is by showing that your theory in practice gives better results than the usual theory. It is usually much easier to see that something works well than it is to understand why it works well, which is another reason why it is better to first show that it works, before trying to explain why it works. Use your theory to make predictions, and then see if those predictions turn out to be better (show less deviation from the observations) than those of the usual theory. If your theory turns out to give better results than the usual theory, and especially if the improvement is considerable, then chances are much better that a scientist will be interested in it. And if your predictions turn out not to be so great after all, then your theory is apparently not quite as good as you thought, so then it is for the better that you didn't bother someone else with it yet.

Why should someone be interested in your theory, if your theory does not give obviously better results than the current theory? It is up to you to show that your work is of interest; it is not up to others to show that your work is not of interest. Many articles are submitted for publication, and there is room for only a small fraction of them. Quality standards are high.

Most prestigious astronomical journals are in English. You can read (older) astronomical publications for free at That should give you an idea of what a scientific astronomical article looks like. You may also be able to read applicable journals if you go to the library of a university where astronomy is taught. In the Netherlands these are mostly in Amsterdam, Leiden and Groningen.


[../../pic/docsleft.gif vorige][../../pic/docsrigh.gif volgende]

languages: [en] [nl];
Last updated: 2016−02−07