101 Matching Annotations
  1. May 2019
    1. rII locus

      A locus is a specific location or section of genetic material. The r<sub>II</sub> locus is one of three loci composing the genetic material of bacteriophage T4 (described below).

    2. From such work it appears that, with minor reservations, each polynucleotide incorporates a characteristic set of amino acids. Moreover, the four bases appear quite distinct in their effects. A comparison between the triplets tentatively deduced by these methods with the changes in amino acid sequence produced by mutation shows a fair measure of agreement. Moreover, the incorporation requires the same components that are needed for protein synthesis and is inhibited by the same inhibitors. Thus, the system is most unlikely to be a complete artifact and is very probably closely related to genuine protein synthesis.

      Scientists often make models to describe something cumbersome and complicated. In the experiments above, the scientists used synthetic RNA as a model for natural genetic material.

      In this paragraph, Crick is assuring us that the results are not an "artifact" of the model: Synthetic RNA is fundamentally the same as natural RNA.

    3. That is, either (+ with + with +) or (- with - with -). Whereas a single + or a pair of them (+ with +) makes the gene completely inactive, a set of three, suitably chosen, has some activity.

      DNA with only one additional base generates a completely different protein than that of the original code. The same is true of DNA with two additional bases.

      However, when bases are added in triplets, the generated protein is identical to the native protein with one minor difference: an extra amino acid.

    4. though a small multiple of 3, such as 6 or 9, is not completely ruled out by our data.

      Scientific knowledge is open to revision in light of new evidence.

    5. This brings us to our first question. Do codons overlap? In other words, as we read along the genetic message do we find a base which is a member of two or more codons?

      Science addresses questions about the natural and material world.

      Great scientists tend to think in terms of questions which guide their discoveries. Good questions keep us curious, objective, and goal-oriented.

    6. protein synthesis

      The process of making proteins.

    7. Let us assume that the genetic code is a simple one and ask how many bases code for one amino acid.

      In other words, how many bases in a row translate into one amino acid?

      Let's do a thought experiment (which is considerably cheaper than a laboratory experiment):

      Assume that each amino acid is coded for by two bases in a row. The code would have one of four different bases in the first position of the code (A, G, C, T) and one of four different bases for the second. How many combinations of pairs would be possible?

      For example: (1) A A (2) A G (3) A C (4) A T (5) G A (6) G G (7) G C (8) G T …

      If you continued to write out every combination, you would come up with 16 possible pairs of bases. However, that's four short of the 20 natural amino acids. This is a good sign that two bases is not enough to code for all possible amino acids (and, in fact, we now know that it takes three bases in a row).

      How many combinations would be possible if the code were a grouping of three bases?

    8. RNA

      Ribonucleic acid, or RNA for short, is one class of genetic material. It is an example of a nucleic acid molecule.

      RNA is composed of three chemical building blocks: a sugar (called ribose), a phosphate group, and a nitrogenous base.

      RNA has many functions in a cell, and scientists are still studying RNA today. Some hope that RNA might be the key to disease prevention.


    9. enzyme

      A special class of proteins which catalyze (i.e., cause or speed up) a chemical reaction in biological systems.

      Remember, that a protein is a chain of amino acids.

    10. amino acid

      The chemical building blocks of proteins. All amino acids contain an amine group (-NH<sub>2</sub>) and a carboxylic acid group (-COOH).


    11. F. H. C. Crick, L. Barnett, S. Brenner, R. J. Watts-Tobin, Nature 192, 1227 (1961)

      In this seminal Nature paper, Crick and co-workers demonstrate that a group of three bases codes for one amino acid; the code does not overlap; the sequence of bases is read from a fixed starting point; and the code is degenerate.

    12. F. H. C. Crick, in Progress in Nucleic Acid Research, J. N. Davidson and Waldo E. Cohn, Eds. (Academic Press, New York, in press).

      This review paper is an extended version of the paper you've read here with sections dedicated to similar questions such as: "Is the code universal?" and "Is the code overlapping?"

    13. The preliminary results presented so far disclose no clear difference, with respect to the code, between E. coli and mammals, and this is encouraging (10, 13).

      Since mammals and E. coli (a bacterium) are extremely different biological species, it is remarkable that their genes are comprised of identical genetic codes. Their similarity suggests the genetic code is not different per species, but universal across all living organisms.

    14. Evidence presented by several groups (8, 9, 11) suggest that poly U stimulates the incorporation of both phenylalanine and a lesser amount of leucine. The meaning of this observation is unclear, but it raises the unfortunate possibility of ambiguous triplets-that is, triplets which may code more than one amino acid. However, one would certainly expect such triplets to be in a minority.

      Now scientists believe that the genetic code is universal, unambiguous, and redundant. In other words, that all living things use the same code, with few exceptions: "universal." That a codon encodes only one amino acid is "unambiguous," but that there are multiple ways to code for the same amino acid is "redundant."

      But what if we could expand the genetic code or reprogram it? Professor Chin of the University of Cambridge explores this possibility here (see also in the Related Resources tab).

    15. Moreover, there is preliminary evidence (9) which suggests that secondary structure within a polynucleotide inhibits the power to stimulate protein synthesis.

      Nirenberg and co-workers saw that poly A was not decoded, specifically at low pH (acidic environments). At low pH, poly A is double stranded. These results suggest that the residues may need to be exposed—that RNA must lack secondary structure—to be decoded.

    16. 2',3' hydroxyls on the sugar.

      Hydroxyls are -OH groups and are found on the sugar ribose on the second and third carbon. In RNA, only one chemical unit in the entire strand has a hydroxyl on both the second and third (2' and 3') carbon.

      Check out this image to identify the hydroxyls found on second and third carbon.

    17. "right-hand" end

      Just as your left and right hands are distinct mirror images, certain molecules have distinct mirror images, too. When a molecule has a distinct mirror image, we say the molecule is chiral.

      All sugars in the body are "right handed." On a strand of genetic material, the sugars are linked together such that only one end of the chain is "handed."

    18. poly (U,C)

      Crick defines poly(Y, Z) as a DNA strand with equal amounts of two bases "Y" and "Z" in random order. Here, poly(U, C) is then a strand of genetic material with equal amounts of uracil and cytosine in random order.

    19. polyuridylic acid

      An RNA molecule in which every base is uracil.

    20. synthetic RNA

      RNA that is made in the lab as opposed to natural RNA found in a cell.

    21. It is believed, not that DNA itself controls protein synthesis directly in a cell in which DNA is the genetic material, but that the base sequence of the DNA - probably of only one of its chains-is copied onto RNA, and that this special RNA then acts as the genetic messenger and directs the actual process of joining up the amino acids into polypeptide chains. The breakthrough in the coding problem has come from the discovery, made by Nirenberg and Matthaei (6)

      Nirenberg and Matthai discovered that "special RNA"—now called tRNA—was critical to protein synthesis. A protein could only grow with enough tRNA available, demonstrating that tRNA was a critical material to generate proteins.

      To hear a contemporary scientist give an in-depth account of protein synthesis, watch Johns Hopkins University's Rachel Green detail the process on this iBiology video.

    22. For example, something very like rabbit hemoglobin can be synthesized in a cell-free system of which part comes from rabbit reticulocytes and part from Escherichia coli (5). That this would be the case if the code was very different in these two organisms is not very probable.

      Lippman and Von Ehrenstein showed that genetic material (mRNA) from a mammal could be decoded with genetic material (tRNA) from a bacteria to form the protein hemoglobin. Because hemoglobin is not found naturally in bacteria but is found naturally in mammals, this was a remarkable result: The biological material of a bacterium decoded mammalian genetic material!

      The result suggests that vastly different biological species share a genetic language. This is strong evidence that the code is universal.

      See a visualization here.

    23. G. von Ehrenstein and F. Lipmann, ibid. 47, 941 (1961)

      Von Ehrenstein and Lipmann demonstrate the genetic materials of a rabbit (a mammal) and E. coli (a bacterium) are compatible, suggesting the genetic code is universal!

    24. The crucial experiment is to put together, by genetic recombination, three mutants of the same type into one gene

      This "frame shift" experiment tests whether the bases are read in singlets, pairs, or triplets.


    25. acridines

      An organic molecule that is not naturally found in cells, as they are substituted derivatives of the parent ring.

      Acridines were previously used in some dyes and many have antiseptic properties, but usage largely stopped since acridines are also a skin irritant.

    26. These mutations are believed to be due to the addition or subtraction of one or more bases from the genetic message. They are typically produced by acridines, and cannot be reversed by mutagens which merely change one base into another. Moreover, these mutations almost always render the gene completely inactive, rather than partly so.

      By incorporating acridine into genetic material, Crick and coworkers produced mutations in DNA. These mutations led to either the addition or subtraction of one base pair in the genetic code.

    27. bacteriophage T4

      A bacteriophage is a type of virus that infects bacteria. The T4 bacteriophage is a specific bacteriophage that infects E coli. Bacteriophages—like all living organisms—have genetic material.

    28. A and B cistrons

      A section of DNA or RNA that codes for a specific chain of amino acids, or "polypeptide chain." Cistron is synonymous with gene, meaning A and B cistrons are two different genes. The term cistron has largely fallen out of favor.

    29. cistron

      A section of DNA or RNA that codes for a specific chain of amino acids, or "polypeptide chain." Cistron is another word for gene. As such, it's not normally used much nowadays.

    30. the amino end

      Imagine kids lined up holding hands: The line leader will have no one to hold her left hand and the caboose will have no one to hold her right hand.

      Amino acids on a protein have a similar feature. The first amino acid will have an amine group exposed and the last amino acid will have an acid group exposed. The "amino end" refers to the end of the strand where the amine group is exposed.

    31. action of nitrous acid and other chemicals on trick tobacco mosaic virus (2)

      Tsugita used an acid (nitrous acid) to chemically mutate RNA. The acid most often changed cytosine bases into uracil bases. The mutant genetic material encoded a different amino acid sequence than the unmutated, or native, form.

    32. Gamow's

      George Gamow (1904–1968) was a theoretical physicist. Curious about the natural world, he was often in contact with scientific giants outside of physics, such as Crick. Despite his inexperience in chemistry and biology, Gamow learned about these fields and ultimately influenced their progress. Gamow is just one of many historical examples of an outside, non-expert perspective having a profound influence on a difficult problem.

    33. Watson

      James Watson (1928–) co-discovered the structure of DNA with Francis Crick (the author of this paper).


    34. Beadle

      George Beadle (1903-1989) was a Nobel Prize-winning scientist credited with discovering the inherent connection between genes (DNA) and enzymes (proteins).


    35. genetic recombination

      The exchange of genetic material between two different organisms. In the case of T4 bacteriophage, this is done by infecting a single E. coli cell with multiple phages. The phage genomes then recombine and produce new variants.

    36. chemically induced mutations

      Chemically induced mutations occur when a scientist uses chemicals to alter a DNA sequence.

    37. messenger RNA

      A class of RNA that acts as a messenger of genetic information, delivering the code from DNA to a ribosome where it is translated into amino acids, eventually resulting in a polypeptide or protein.

    38. a sequence of 20 or more things is determined by a sequence of four things of a different type.

      That is, a specific sequence of bases encodes a specific sequence of amino acids. Within this code, which is used by all living organisms, there are only four kinds of bases and 20 kinds of amino acids.

    39. bases

      Here, bases refer to the chemical pendants—side groups of molecules—that are found on the backbone of nucleotides. Nucleotides consist of a sugar called deoxyribose, a phosphate group, and one of five bases.

      An example of a base is guanine.

    40. This article is adapted from the lecture which he delivered in Stockholm, Sweden, 11 December 1962, on receiving the Nobel prize in medicine and physiology, a prize which he shared with James D. Watson and M. H. F. Wilkins. It is published with the permission of the Nobel Foundation.

      Francis Crick, James Watson, and Maurice Wilkins published the seminal papers about the structure of DNA, winning them the Nobel Prize in 1962. Rosalind Franklin was a major contributor to the discovery; her experimental evidence was critical for understanding DNA's structure.

      Rosalind Franklin has often been uncredited and overshadowed in this historical discovery. Read more here and here.

  2. Apr 2019
    1. It seems likely, then, that most of the 64 possible triplets will be grouped into 20 groups.

      Scientists have since tried to extend the genetic code to encode for more than the 20 natural amino acids. Read more in Science.

    2. polyphenylalanine

      Poly means many and phenylalanine is a specific amino acid. Therefore, polyphenylalanine is a chain of many phenylalanine residues.

    3. carboxyl end

      The carboxyl end refers to the carboxylic acid group exposed on the protein chain. (Remember the analogy of kids lined up holding hands? This is in the Glossary annotation of "amino end.")

    4. codon

      A set of nucleotide bases which codes for one amino acid.

    5. mutagens

      An agent that changes one base into another either by chemical methods or radiation. Acridine is not a mutagen since it does not modify existing bases in DNA, but rather adds or deletes bases.

    6. hemoglobins

      The iron-rich proteins in our red blood cells that transport oxygen from our lungs to the rest of our body.

    7. Twenty different kinds of amino acid are commonly found in protein, and four main kinds of base occur in nucleic acid.

      See the supplemental figure below.

  3. Feb 2019
    1. This fits in very well with the experimental evidence, most clearly shown in the work of Dintzis (4), that the amino acids are assembled into the polypeptide chain in a linear order, starting at the amino end of the chain

      Dintzis and Naughton demonstrated that a protein is synthesized from one end of the amino acid chain to the other, like stringing beads on a necklace one by one.

    2. It appears that the number of nonsense triplets is rather low, since we only occasionally come across them.

      Crick has evidence from his frameshift experiments that some triplets do not code for any amino acids, but these triplets are rare.

    3. Detailed examination of these results shows that they' are exactly what we should expect if the message were read in triplets, starting from one end.

      By adding and subtracting bases from the genetic code, certain patterns arose. These patterns were consistent with three bases coding for one amino acid.

    4. If, for example, all the codons are triplets, then in addition to the correct reading of the message there are two incorrect readings which we shall obtain if we do not start the grouping into sets of three at the right place.

      For example, if a DNA sequence contains ...CCGGAUC...

      Then an individual codon might be (1) CCG (2) CGG or (3) GGA. One of these would be correct and the other two incorrect.

  4. Nov 2018
    1. polypeptide chain

      A chain of amino acids.

    2. M. S. Bretscher and M. Grunberg-Manago, Nature 195, 283 (1962).

      Bretscher and Grunberg-Manago debunk the hypothesis that all codons must contain uracil by analyzing the coded proteins from poly(C, A).

    3. A start has been made to construct polynucleotides whose exact sequence is known at one end, but the results obtained so far are suggestive rather than conclusive (12).

      The 1980 Nobel Prize in chemistry went to Paul Berg, Walter Gilbert, and Frederick Sanger for successfully sequencing DNA! This scientific feat is now commonplace, generating a mixed response of enthusiasm and concern.

      Read more at NPR.org:


    4. It now seems fairly certain that codons do not overlap. If they did, the change of a single base, due to mutation, should alter two or more (adjacent) amino acids, whereas the typical change is to a single amino acid,

      If codons do not overlap, then a single base change would alter the code for only a single amino acid. If codons do overlap, then a single base change may alter the code for multiple amino acids.

    5. presumably AAA codes lysine. However, since UUU codes phenylalanine, these facts rule out all the foregoing proposed codes.

      Since the complement base to A is U, the complementary code hypothesis would suspect AAA to code the same amino acid as UUU. Instead, AAA codes for a different amino acid (lysine) than UUU (phenylalanine), ruling out the complementary code hypothesis.

    6. The first direct evidence that this was not so was obtained by my colleagues Bretscher and Grunberg-Manago (8), who showed that a poly (C,A) would stimulate the incorporation of several amino acids.

      Since a strand of RNA lacking uracil encoded for various amino acids, uracil is not necessary to encode for an amino acid.

    7. Thus, one codon for phenylalanine appears to be the sequence UUU

      Since the only base found on the synthetic RNA was uracil (U), Crick concludes that triplets of uracil must encode phenylalanine residues.

    8. postulates

      An unproven principle assumed to be true for the basis of further discussion or logical reasoning.

    9. We are sometimes asked what the result would be if we put four +'s in one gene. To answer this my colleagues have recently put together not merely four but six +'s. Such a combination is active, as expected on the basis of our theory, although sets of four or five of them are not.

      This experiment is an extension of the frameshift experiment. If the bases are read in triplets, then you'd expect that four or five extra bases would ruin the code. However, six extra bases would still encode the amino acids for the native protein (with two extra amino acid residues).

    10. The number of triplets which do not code an amino acid is probably small.

      Scientists now call these STOP codons.

    11. mutation

      A change in the DNA base sequence. There are many types of mutations, but here Crick refers to changing a single base of DNA (a point mutation).

    12. "spontaneous" mutations

      A mutation that occurs naturally in biochemical systems.

    13. gene

      A section of DNA or RNA that codes for a specific chain of amino acids.

    14. nucleic acid molecule

      A chemical chain made up of nucleotides. "Bases" (see previous) are one component of a nucleotide.

    15. protein

      A chemical chain of amino acids.

  5. Oct 2018
    1. DNA

      Deoxyribonucleic acid, or DNA for short, is one class of genetic material. It is an example of a nucleic acid molecule.

      DNA is composed of three chemical building blocks: a sugar (called deoxyribose), a phosphate group, and a nitrogenous base.

  6. Sep 2018
    1. After the lamentable breach in the former international relations existing among men of science, it is with joy and gratefulness that I accept this opportunity of communication with English astronomers and physicists.

      Einstein's letter was originally published in the 28 November 1919 issue of The Times, a British daily national newspaper.

      During the war, Einstein lived and worked in Berlin, Germany. Communication between England and Germany seems to have been limited during the war, even among scientists in those countries. Because science is a collaborative endeavor that spans countries and cultures, Einstein understandably appreciates the renewed communication between these two important countries.

  7. Aug 2018
    1. It was in accordance with the high and proud tradition of English science that English scientific men should have given their time and labor, and that English institutions should have provided the material means, to test a theory that had been completed and published in the country of their enemies in the midst of war.

      Einstein published his equations that describe gravity with respect to space and time in 1915 —right in the middle of World War I (1914-1918).

      Despite poor political relations during this period, two Englishmen published experimental evidence that supported Einstein's theory. Einstein commended the English scientists and institutions for prioritizing scientific pursuits over politics.

    2. The shifting of spectral lines towards the red end of the spectrum in the case of light coming to us from stars of appreciable mass (not yet confirmed).

      In 1959, the Pound–Rebka experiment confirmed that light moving out of a gravitational well is in fact red-shifted.

      Read more in The New York Times:


    3. 1The distortion of the oval orbits of planets round the sun (confirmed in the case of the planet Mercury).

      In A New Determination of the Orbit of Mercury and its Perturbations (1843), Urbain Jean Joseph Le Verrier reported a peculiar precession of Mercury's orbit that was not accounted for by Newtonian mechanics.

      Relativity theory, however, provides a robust account of Mercury's motion.

    4. In the generalized theory of relativity, the doctrine of space and time, kinematics, is no longer one of the absolute foundations of general physics. The geometrical states of bodies and the rates of clocks depend in the first place on their gravitational fields, which again are produced by the material systems concerned.

      General relativity theory expands special relativity theory to include any reference frame (not just inertial ones).

      With no constant frame of reference, general relativity theory cannot consider space and time as separable entities.

      Instead, general relativity theory describes something called "space-time" which is warped by massive bodies. Objects traveling through space-time that has been warped by these bodies will follow a warped path (even though it may appear "straight" to the object). We call this effect "gravity."

    5. solids

      Solids are 3D objects, such as cubes, spheres, or pyramid structures.

    6. Euclidian geometry

      Euclid was a mathematician in Ancient Greece. His book Elements is arguably the first mathematics textbook. In the text, Euclid describes the geometry we seem to experience in our everyday lives in which parallel lines do not intersect.

      This is also the same geometry we still learn in high schools across the country (2000 years after Euclid wrote it).

    7. inert and heavy masses

      Inert mass (m) is conceptually different from heavy mass (M). Heavy mass is a value that determines the strength of gravitational attraction, whereas inert mass (or inertial mass) is a value that indicates how resistant a thing is to a change of motion.

      Modern physicists use the term "gravitational mass" instead of "heavy mass."

    8. The application of this general theory of relativity was found to be in conflict with a well-known experiment, according to which it appeared that the weight and the inertia of a body depended on the same constants

      The Eötvös experiment measured the correlation between inert and heavy mass (or inertia of a body and its weight) and showed that these two masses have the same value although are conceptually distinct.

    9. Although it may be necessary for our descriptions of nature to employ systems of coordinates that we have selected arbitrarily, the choice should not be limited in any way so far as their state of motion is concerned.

      General relativity theory allows us to describe space and time regardless of a choice of coordinate systems or reference frames.

      Unlike special relativity, general relativity does not assume an inertial (i.e., static) frame of reference..

    10. physical laws

      Physical laws are mathematical expressions that generalize physical phenomena. Physical laws explain and predict experimental results. Conservation of energy (ΔE=0) is one example of a physical law.

    11. It became evident that the inertia of such a system must depend on its energy content, so that we were driven to the conception that inert mass was nothing else than latent energy. The doctrine of the conservation of mass lost its independence and became merged in the doctrine of conservation of energy.

      Special relativity theory concludes a relationship between mass and energy (E=mc<sup>2</sup>).

      Therefore, the theory marries the conservation of mass and conservation of energy as one and the same law.

    12. It became evident that a statement of the coincidence of two events could have a meaning only in connection with a system of coordinates, that the mass of bodies and the rate of movement of clocks must depend on their state of motion with regard to the coordinates.

      Einstein states a major consequence of special relativity: We can only say two events occur simultaneously when those events share a system of coordinates.

      We can always put two events into the same coordinate system, but whether they are simultaneous depends on which coordinates we use.

      Einstein uses a famous thought experiment to describe this. Imagine a train traveling on railway tracks and equidistant between two trees (one ahead, one behind). If lightning strikes both trees at the same time, an observer on the train will see the lightning strike ahead before the lightning strike behind. However, an observer standing still next to the tracks (also equidistant between the trees) will see both at the same time. Thus, whether the lightning strikes are simultaneous depends on the observer's frame of reference.

    13. kinematics

      Kinematics is a branch of mechanics concerned with the geometry of motion.

      (Einstein clarifies what he means by "kinematics" throughout the paper. When Einstein says kinematics, he specifically refers to the physics that treats space and time as separable entities.)

    14. The second principle on which the special relativity theory rests is that of the constancy of the velocity of light in a vacuum. Light in a vacuum has a definite and constant velocity, independent of the velocity of its source.

      This is the second principle of special relativity:

      Light can be thought of as many particles (called photons) that move through space. These particles always travel at the same constant speed regardless of the inertial system in which light is observed. This has been well established by the work of many physicists.

      This means that it does not matter how fast you travel towards or away from a source of light—it will always travel at a constant velocity, the speed of light.

    15. inertia-system

      An inertia system of coordinates is a coordinate system that we can approximate to be stationary.

      For instance, we can describe the displacement of a baseball (the object of interest) relative to the baseball field (an inertia system of the baseball). Since both the baseball and the field are subject to the same rotational motion of Earth, the movement of the baseball can be described relative to the seemingly stationary field.*

      Einstein gives us a way to determine if a system of coordinates is an inertia system:

      A system of coordinates moving in the same direction and at the same rate as a system of inertia is itself a system of inertia.

      *For the purposes of this example, we have ignored the (negligible) effect of Earth's rotation. An observer on the surface of Earth must be accelerating to follow a circular path, and the entire system is subject to the non-inertial effects of gravity.

    16. systems of coordinates

      Systems of coordinates indicate the location of a point in space in reference to some other point. In doing so, systems of coordinates form a mathematical map of physical space.

      In Einstein's example, the system of coordinates for the railway train is the ground.

    17. the analytic, not the synthetic method

      Einstein says the analytic method is used to form theories of principle, whereas the synthetic method is used to form constructive theories. We can understand the methods as contrasts.

      The synthetic method supposes premises that help explain natural phenomena, while the analytic method reduces all natural phenomena to their common denominator. The synthetic method is a bottom-up approach, whereas the analytic method is a top-down approach.

      Another way to think about the difference is that the analytical approach starts with observations, whereas the synthetic method starts with hypotheses.

      (For those who are philosophy-inclined, Immanuel Kant discusses this distinction between the analytic and the synthetic.)

    18. kinetic theory of gases

      The kinetic theory of gases describes the motion of atoms in the gas phase and makes a number of assumptions such as:

      1. The gas molecules have negligible volume compared to their container.
      2. The molecules are constantly moving.
      3. All collisions are perfectly elastic.
  8. Jul 2018
    1. Since the time of the ancient Greeks it has been well known that in describing the motion of a body we must refer to another body.

      Aristotle contemplates absolute and relative motion in his book On the Heavens. He describes how heavy bodies move down and lighter bodies (like air or fire) move up relative to the center of the universe.

      Read more: https://plato.stanford.edu/entries/spacetime-theories/#2

    2. theory of relativity

      Einstein's theory of relativity is a two-part theory. Together, the two parts explain the motion of subatomic particles and gargantuan masses and address some of the shortcomings of earlier theories of motion.

      The theory is well known for combining the concepts of space and time, revealing that they are inseparable.

    3. The deviation of light-rays in a gravitational field (confirmed by the English Solar Eclipse expedition).

      Again, this was found by Arthur Eddington and Frank Watson Dyson in their paper.

    4. Maxwell-Lorentz theory

      Maxwell's equations describe how electric and magnetic fields manifest from charged particles. Together, Maxwell's equations suggest the speed of electromagnetic waves (i.e. light) is constant.

      The Lorentz Force Law says that the force felt by some charged particle is related to the surrounding electric and magnetic fields.

      Together their work describes special relativity, but only for electromagnetism.

    5. empirically

      Empirical methods involve observation and experience, rather than logical deduction alone.

    6. I am none the less very glad to express my personal thanks to my English colleagues in this branch of science; for without their aid I should not have obtained proof

      Einstein's "English colleagues" are Arthur Eddington and Frank Watson Dyson, astronomers who obtained experimental evidence of Einstein's theory of relativity.

      Modern physicists have debated whether the error bars in the Eddington experiment were larger than the effect they measured. Nevertheless, the results have been confirmed.

      Read Eddington and Dyson's work here.

    7. rays of light

      In the image below, the solar gravitational field influences the sun's rays framing the moon. Notice that the light bends around the moon due to the gravitational field, rather than forming a spherical halo.

    8. inert mass

      A value that indicates how resistant a thing is to a change of motion.

      Modern physicists use the term "inertial mass" instead of "inert mass."

  9. May 2018
    1. Maxwell and Lorentz,

      James Clerk Maxwell and Hendrik Antoon Lorentz were physicists of the late 1800s and early 1900s. Their work is the foundation of the branch of physics called electromagnetism.

    2. The special relativity theory is therefore the application of the following proposition to any natural process: "Every law of nature which holds good with respect to a coordinate system K must also hold good for any other system K' provided that K and K' are in uniform movement of translation."

      This is the first principle of Special Relativity:

      The laws of physics are the same for all observers in uniform motion relative to one another.

    3. theories of principle

      This is the second kind of theory that Einstein delineates. He tells us that a theory of principle is one that is formed from the most consistent and basic observations seen across all natural phenomena.

    4. constructive

      A constructive theory is one that is built up (i.e., constructed) from assumptions to explain a natural phenomenon.

    5. proposition

      A proposition states a claim that can be either true or false.

    6. Thermodynamics

      The science that studies the relationship between heat (thermo) and work or movement (dynamic).

  10. Apr 2018
    1. solar gravitational field

      The region of space around the sun that is attractive to other massive bodies (i.e., the planets).