Physics

This article provides answers to the questions posed in the title. Contrary to the most common views, we show that neither the entropy, nor the Second Law may be used for either living systems, or to life phenomenon.

Captain Einstein is a virtual reality (VR) movie that takes you on a boat trip in a world with a slow speed of light. This allows for a direct experience of the theory of special relativity, much in the same spirit as in the Mr. Tompkins adventure by George Gamow (1939). In this paper we go through the different relativistic effects (e.g. length contraction, time dilation, Doppler shift, light aberration) that show up during the boat trip and we explain how these effects were implemented in the 360 video production process. We also provide exercise questions that can be used - in combination with the VR movie - to gain insight and sharpen the intuition on the basic concepts of special relativity.

Until recently, the only way to observe the Universe was from light received by telescopes. But we are now able to measure gravitational waves, which are ripples in the fabric of the Universe predicted by Albert Einstein. If two very dense objects (like black holes) orbit each other closely, they warp space and send out gravitational waves. For black holes that are similar in mass to the Sun, scientists use the LIGO detector on Earth. But for the biggest black holes in the Universe (billions of times more massive than the Sun), scientists monitor a net of rapidly-spinning neutron stars (called pulsars) across the Milky Way. Any gravitational wave passing by will change how long radio signals from these pulsars take to get to Earth. The NANOGrav Collaboration monitored 34 of these pulsars over 11 years, in an attempt to detect gravitational waves from giant black holes.

Even if it tends to hide more often in the current autumnal season, our host star, the Sun, is the principal source of energy on our planet. It has a luminosity of 3.828e26 Watts, and despite that we receive only 2 parts per billion of this, it allows for the Earth's life to thrive. Moreover, we know that the Sun has been shining in the same way for about 4.6 billion years (the age of the Earth) and will likely still do the same for another 5 billion years or so. The Sun's power engine, as well as the one of all the stars we see in the night sky, has for long been a mystery, but astronomers now have a good understanding of it.

Chirality, or handedness, is a topic that is common in biology and chemistry, yet is rarely discussed in physics courses. We provide a way of introducing the topic in classical physics, and demonstrate the merits of its inclusion - such as a simple way to visually introduce the concept of symmetries in physical law - along with giving some simple proofs using only basic matrix operations, thereby avoiding the full formalism of the three-dimensional point group.

The engagement of Citizen Scientists with the this http URL citizen science project is investigated through analysis of behaviour, discussion, and survey data. More than 37,000 Citizen Scientists from 179 countries participated, classifying 1,500,000 features of interest on about 39,000 distinct images. While most Citizen Scientists classified only a handful of images, some classified hundreds or even thousands. Analysis of frequently-used terms on the dedicated discussion forum demonstrated that a high level of scientific engagement was not uncommon. Evidence was found for a emergent and distinct technical vocabulary developing within the Citizen Science community. A survey indicates a high level of engagement and an appetite for further LHC-related citizen science projects.

Air travel has become one of the most common means of transportation. The most common question which is generally asked is: How does an airplane gain lift? And the most common answer is via the Bernoulli principle. It turns out that it is wrongly applied in common explanations, and there are certain misconceptions. In an alternative explanation the push of air from below the wing is argued to be the lift generating force via Newton's law. There are problems with this explanation too. In this paper we try to clear these misconceptions, and the correct explanation, using the Lancaster-Prandtl circulation theory, is discussed. We argue that even the Lancaster-Prandtl theory at the zero angle of attack needs further insights. To this end, we put forward a theory which is applicable at zero angle of attack. A new length scale perpendicular to the lower surface of the wing is introduced and it turns out that the ratio of this length scale to the cord length of a wing is roughly 0.4930±0.09498 for typical NACA airfoils that we analyzed. This invariance points to something fundamental. The idea of our theory is simple. The "squeezing" effect of the flow above the wing due to camber leads to an effective Venturi tube formation and leads to higher velocity over the upper surface of the wing and thereby reducing pressure according the Bernoulli theorem and generating lift. Thus at zero angle of attack there is no need to invoke vortex and anti-vortex pair generation. In fact vortex and anti-vortex pair generation cannot be justified. We come up with the equation for the lift coefficient at zero angle of attack: C l = 1 c ∫ c 0 dx( h 2 c ( h c −f(x) ) 2 −1). Here C l is the lift coefficient, h c is our new length scale perpendicular to the lower surface of the wing and f(x) is the functional profile of the upper surface of the wing.

Many papers and monographs were written about the modeling the Earth climate and its variability. However there is still an obvious need for a module that presents the fundamentals of climate modeling to students at the undergraduate level. The present educational paper attempts to fill in this gap. To this end we collect in this paper the relevant climate data and present a simple zero and one dimensional models for the mean temperature of the Earth. These models can exhibit bifurcations from the present Earth climate to an ice age or a "Venus type of climate". The models are accompanied by Matlab programs which enable the user to change the models parameters and explore the impact that these changes might have on their predictions on Earth climate.

Newton famously showed that a gravitational force inversely proportional to the square of the distance, F∼1/ r 2 , formally explains Kepler's three laws of planetary motion. But what happens to the familiar elliptical orbits if the force were to taper off with a different spatial exponent? Here we expand generic textbook treatments by a detailed geometric characterisation of the general solution to the equation of motion for a two-body `sun/planet' system under anomalous gravitation F∼1/ r α (1≤α<2) . A subset of initial conditions induce closed self-intersecting periodic orbits resembling hypotrochoids with perihelia and aphelia forming regular polygons. We provide time-resolved trajectories for a variety of exponents α , and discuss conceptual connections of the case α=1 to Modified Newtonian Dynamics and galactic rotation curves.

The human mind is endowed with innate primordial perceptions such as space, distance, motion, change, flow of time, matter. The field of cognitive science argues that the abstract concepts of mathematics are not Platonic, but are built in the brain from these primordial perceptions, using what are known as conceptual metaphors. Known cognitive mechanisms give rise to the extremely precise and logical language of mathematics. Thus all of the vastness of mathematics, with its beautiful theorems, is human mathematics. It resides in the mind, and is not `out there'. Physics is an experimental science in which results of experiments are described in terms of concrete concepts - these concepts are also built from our primordial perceptions. The goal of theoretical physics is to describe the experimentally observed regularity of the physical world in an unambiguous, precise and logical manner. To do so, the brain resorts to the well-defined abstract concepts which the mind has metaphored from our primordial perceptions. Since both the concrete and the abstract are derived from the primordial, the connection between physics and mathematics is not mysterious, but natural. This connection is established in the human brain, where a small subset of the vast human mathematics is cognitively fitted to describe the regularity of the universe. Theoretical physics should be thought of as a branch of mathematics, whose axioms are motivated by observations of the physical world. We use the example of quantum theory to demonstrate the all too human nature of the physics-mathematics connection: it is at times frail, and imperfect. Our resistance to take this imperfection sufficiently seriously [since no known experiment violates quantum theory] shows the fundamental importance of experiments in physics.