Institute of Astronomy

Lucky and Dark Matter

Lucky Imaging and Dark Matter

This section of the instrumentation webpages covers two rather different technological challenges, Lucky Imaging and whether Dark Matter and Dark Energy really exist.

Lucky Imaging.

Firstly the search for instruments that will allow astronomers to achieve much higher angular resolution in the optical and infrared part of the spectrum with large modern telescopes and advanced instrumentation. This can be found on the next tab entitled "High Resolution Imaging", with the full link here: https://www.ast.cam.ac.uk/research/instrumentation.surveys.and.projects/lucky.imaging/aoli

Subsequent tabs examine different aspects of the technologies that people have used in recent years for these goals.

Dark Matter and Dark Energy.

The second challenge is to try and understand why all the attempts at detecting dark matter and dark energy have failed to produce any results. We have looked at those astronomical objects believed to be reservoirs of considerable amount of dark matter to find out why they have not been found. The conclusion turns out to be a rather simple one. Using Newtonian gravitation published over 300 years ago does not give an adequate explanation of the complexity of dynamics routinely found in astronomy. Only by using Einstein's gravitation theories which are just over 100 years old we find there is no real evidence for the existence of dark matter or indeed of dark energy.

A relatively short summary is given here together with a link here to a more detailed research paper which should be understandable by anyone with an interest in physics and astronomy. It has many references to research papers that have provided the information we need. There is also a link to a video of the talk on the subject which also should be entirely suitable for general consumption. It lasts about 45 minutes.

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On the Invention of Dark Matter and Dark Energy: Full paper HERE.

Introduction.

Dark matter and dark energy were each introduced as concepts in order to make specific astronomical observations fit in with the then understanding of the physics involved.  A great deal of money and effort has gone into attempts to detect dark matter and, more recently, dark energy yet all to no avail.  Our lack of success in detecting dark matter may be a consequence of not knowing what to look for or indeed not having adequate sensitivity in our detectors.  The other reason for us not detecting dark matter may be because it simply does not exist, and the physics employed to justify its existence is in error.  That second explanation is what we explore here.

The Invention of Dark Matter.

All massive objects such as our Sun are embedded in a gravitational field. Much lighter objects such as the planets orbit the Sun in ways that can be described using Newton’s gravitation. However that only works because the solar system is dominated by the mass of the spherical Sun. However, if an object is quite asymmetric as are spiral galaxies then using Newton’s gravitation led astronomers to believe that there was a substantial amount of invisible, dark matter in the galaxy to stop them flying apart (McGaugh et al, 2016).

The gravitational field has energy and therefore a mass of its own that is neglected by Newton’s gravitation. Einstein was able to predict accurately the deflection of starlight by the sun during a solar eclipse at the beginning of the 20th century by including the effects of the gravitational field (Einstein et al, 1938). Einstein’s theory addresses this more generally producing results that are significantly different. These imply there is no such dark matter in most galaxies. The galaxies are found to be stable as we observe them without any recourse to dark matter.

The Invention of Dark Energy.

Another consequence of using Einstein’s gravity is that the gravitational force exerted by an asymmetric galaxy on another is somewhat diminished. This is because some of the gravitational field energy is used up in binding the galaxy together. If we ignore Einstein’s gravity and this slightly weaker interaction then this can give the impression that there exists a negative force causing galaxies to fly apart. In reality there is no need for this negative force also called dark energy and attributed to a nonzero cosmological constant. Although such a constant is allowed in Einstein’s cosmologies it is not necessary to explain the relatively modest discrepancies in the apparent distances of a range of supernovae events. These can be understood as a natural consequence of a slight reduction in the gravitational field energy consequent on the way that galaxies evolve time.

The Growth of Structures without Dark Matter

We know that the universe was remarkably uniform in its earliest days from studies of the cosmic microwave background. This made it more difficult to understand how the galaxies and clusters of galaxies we see around us had enough time to form given its relatively uniform beginnings. Cosmologists suggested that there must be a very substantial amount of dark matter in the universe which would accelerate the formation of these larger structures. However using Einstein’s gravitation correctly we find that structure formation occurs naturally without there being any place for dark matter or indeed the cosmological constant. Most importantly some of the key features of modern cosmology such as the prediction of the spectrum of baryonic acoustic oscillations is well reproduce with Einstein’s gravitation once we stop assuming that the universe is homogeneous and isotropic. The universe around us now is very far from that.

Conclusions.

Einstein’s theory of general relativity is used very successfully in many other branches of physics. When scientists ignore such a fundamentally important theory it is inevitable that mistakes will creep in. That is what we seem to have here. There is no evidence at all for dark matter or dark energy, or indeed for the necessity of the cosmological constant to explain the structure of our universe. The consequence of these discoveries is that expensive experimental and theoretical attempts to understand and ultimately detect dark matter and dark energy simply cannot be justified any longer.

References

Einstein, A., Infeld, L., & Hoffmann, B. 1938, Annals of Mathematics, 39, 65.
McGaugh, S. S., Lelli, F., & Schombert, J. M. 2016, Phys.Rev. Lett., 117, 201101,

6 December 2021, Craig Mackay.