- Email: [email protected]
Lunar lift
Last words past and present at newscientist.com/lastword
THE LAST WORD Galaxy twirl
in my whiskers. I understand the loss of pigmentation occurring, but why are the grey hairs growing more slowly than the darker ones? This discrepancy is clearly noticeable if I stop shaving for a few days. Peter Milne, Brunswick, Victoria, Australia
Are the spiral arms of galaxies evidence for gravitational waves? If not, what creates these arms?
n Spiral arms are not evidence for gravitational waves. According to density wave theory, they are regions in which the density of gas and stars is much higher and this matter moves more slowly than in the regions between the arms. This theory explains how the spiral arms form in the first place – and once formed, they are self-sustaining. Material that approaches a spiral arm speeds up because of the extra mass in the arm and then slows down while passing through it. This triggers intensive star formation, leading to the birth of massive and luminous stars that have relatively short lifespans (millions of years) compared with our sun (billions of years). These types of star die in supernova explosions before they
Bloodthirst
Do humans have an innate desire to eat meat, or is it cultural? If our culture had all references to eating meat removed, would people still desire it? Richard Brown Geneva, Switzerland
have time to leave the spiral arm. Only stars with a low mass, such as the sun, can leave the spiral arm and orbit the galactic centre to eventually return to their birthplace. Chris Brindle, Bodmin, Cornwall, UK
n There is a possible method for spiral galaxies to form without invoking mysterious forces. I have in my possession a harmonograph, which is a drawing toy that comprises two pendulums. One pendulum is attached to a table for paper, and the other a pen. It is not difficult to arrange for a decreasing spiral to be drawn. We can consider those spirals as a set of concentric nested circles, representing a uniform disc of matter. All of these orbit the central point in the expected manner, with things remaining uniform and the orbital rate of each “band” not affecting the distribution in the disc too much. But if a remote galaxy or disturbance nudges the orbits into a slightly elliptical shape, then the fun begins. The images shown above are from my collection. The lines
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
“Only stars with a low mass, such as the sun, can leave the spiral arm and orbit the galactic centre”
represent material of uniform density, and the precession, or uneven motion, causes the overlapping areas. Because the orbital rate has a gradient across it (for example, the outer orbits take slightly longer than the inner orbits), the matter will slowly group together in the density pattern shown in the harmonograph. The resemblance to a spiral galaxy is astonishing, and nothing non-Newtonian is involved. It is very hypnotic watching these being drawn. Dennis Cowdery Brimpton, West Berkshire, UK
This week’s questions Old growth
I’m a 55-year-old man with an increasing number of grey hairs
PEOPLE-TASTING
What do humans taste of? I have heard that it’s a little bit like pork (not that I want to find out). But if it is, why? And if it isn’t, what do they taste of? Also, why do different meats – say lamb, beef, chicken or pork – taste different anyway? Brian Bott Paris, France Lunar lift
Tides are affected by the moon’s gravity. So does your weight change depending on its position? Priyã-Louan Macknay By email, no address supplied Clean break
I’ve discovered that glasses with a thick base crack around the bottom when cleaned in the dishwasher. Why is this? Tony Sandy Kilmarnock, East Ayrshire, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything
THE LAST WORD Galaxy twirl
in my whiskers. I understand the loss of pigmentation occurring, but why are the grey hairs growing more slowly than the darker ones? This discrepancy is clearly noticeable if I stop shaving for a few days. Peter Milne, Brunswick, Victoria, Australia
Are the spiral arms of galaxies evidence for gravitational waves? If not, what creates these arms?
n Spiral arms are not evidence for gravitational waves. According to density wave theory, they are regions in which the density of gas and stars is much higher and this matter moves more slowly than in the regions between the arms. This theory explains how the spiral arms form in the first place – and once formed, they are self-sustaining. Material that approaches a spiral arm speeds up because of the extra mass in the arm and then slows down while passing through it. This triggers intensive star formation, leading to the birth of massive and luminous stars that have relatively short lifespans (millions of years) compared with our sun (billions of years). These types of star die in supernova explosions before they
Bloodthirst
Do humans have an innate desire to eat meat, or is it cultural? If our culture had all references to eating meat removed, would people still desire it? Richard Brown Geneva, Switzerland
have time to leave the spiral arm. Only stars with a low mass, such as the sun, can leave the spiral arm and orbit the galactic centre to eventually return to their birthplace. Chris Brindle, Bodmin, Cornwall, UK
n There is a possible method for spiral galaxies to form without invoking mysterious forces. I have in my possession a harmonograph, which is a drawing toy that comprises two pendulums. One pendulum is attached to a table for paper, and the other a pen. It is not difficult to arrange for a decreasing spiral to be drawn. We can consider those spirals as a set of concentric nested circles, representing a uniform disc of matter. All of these orbit the central point in the expected manner, with things remaining uniform and the orbital rate of each “band” not affecting the distribution in the disc too much. But if a remote galaxy or disturbance nudges the orbits into a slightly elliptical shape, then the fun begins. The images shown above are from my collection. The lines
The writers of answers that are published in the magazine will receive a cheque for £25 (or US$ equivalent). Answers should be concise. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and an email address if you have one. New Scientist retains total editorial control over the published content. Reed Business Information Ltd reserves all rights to reuse all question and answer material that has been
submitted by readers in any medium or in any format and at any time in the future. Send questions and answers to The Last Word, New Scientist, 110 High Holborn, London WC1V 6EU, UK, by email to [email protected] or visit www.newscientist.com/topic/lastword (please include a postal address in order to receive payment for answers). Unanswered questions can also be found at this URL.
“Only stars with a low mass, such as the sun, can leave the spiral arm and orbit the galactic centre”
represent material of uniform density, and the precession, or uneven motion, causes the overlapping areas. Because the orbital rate has a gradient across it (for example, the outer orbits take slightly longer than the inner orbits), the matter will slowly group together in the density pattern shown in the harmonograph. The resemblance to a spiral galaxy is astonishing, and nothing non-Newtonian is involved. It is very hypnotic watching these being drawn. Dennis Cowdery Brimpton, West Berkshire, UK
This week’s questions Old growth
I’m a 55-year-old man with an increasing number of grey hairs
PEOPLE-TASTING
What do humans taste of? I have heard that it’s a little bit like pork (not that I want to find out). But if it is, why? And if it isn’t, what do they taste of? Also, why do different meats – say lamb, beef, chicken or pork – taste different anyway? Brian Bott Paris, France Lunar lift
Tides are affected by the moon’s gravity. So does your weight change depending on its position? Priyã-Louan Macknay By email, no address supplied Clean break
I’ve discovered that glasses with a thick base crack around the bottom when cleaned in the dishwasher. Why is this? Tony Sandy Kilmarnock, East Ayrshire, UK
Question Everything The latest book of science questions: unpredictable and entertaining. Expect the unexpected Available from booksellers and at newscientist.com/questioneverything