Faster than light??? Nope!

[MargaritaMc]

Click to play embedded YouTube video.

http://earthsky.org/space/video-will-th ... than-light
Canadian science communicator Derek Muller has a great new video on his YouTube channel Veritasium explaining the physics of contraptions meant to go faster than light. He shows how things get weird really fast in these situations, and explains why the speed of light – 186,000 miles per second (300,000 km/sec) – appears to be our universe’s ultimate speed limit. You’ll enjoy all six minutes of it.

There is an advert at the end, so it's slightly less than six minutes long.
M

[neufer]

Who composed the limerick:
There Was a Young Lady Named Bright... ?
Quote Investigator, December 19, 2013

<<The earliest evidence known to QI appeared in an issue of the London humor magazine “Punch” in 1923.
Initially, the limerick “Relativity” was published without attribution:

• • Relativity.
  There was a young lady named Bright
  Whose speed was far faster than light;
  She set out one day
  In a relative way
  And returned on the previous night.

In 1937 A. H. Reginald Buller wrote a letter to “The Observer” newspaper in London and claimed authorship of the limerick. A. H. Reginald Buller was a Professor of Botany at the University of Manitoba. In April 1927 the “Manitoba Free Press” which is also based in Winnipeg printed a version of the limerick, and this time Buller was credited. Buller discussed the circumstances of its composition:

• As the author of the Relativity limerick perhaps I may be allowed to say that the limerick was made by me about fifteen years ago whilst sitting in the garden of my friend and former colleague, Dr. G. A. Shakespear, Lecturer on Physics at the University of Birmingham. After conversing together on Einstein’s theory, I suggested that we should each try to make a relativity limerick. At the end of about five minutes the limericks were ready and were exchanged, but with nothing more than a trace of mutual admiration.
  
  Buller stated that two years later he attended a scientific meeting, and he recited the limerick to fellow scientists who laughed and applauded. Shortly afterward a reporter for the “Winnipeg Free Press” told him that the work should be submitted to “Punch”:
  
  On arriving at the university I wrote out the limerick and at once sent it off to Punch. Six weeks later I received from the editor a copy of “Punch” with my limerick in it, and an honorarium of a few shillings. The date of publication was December 19, 1923.
  
  Since the relativity limerick was published I have noted that at various times it has been attributed to three bishops and to a well-known American authoress!—Yours etc.,
  
  • A. H. Reginald Buller,
    Emeritus Professor of Botany, University of Manitoba.
    Royal Botanic Gardens, Kew.>>

[Ann]

But you're right - carbon nanotubes are tremendously strong. If you had a fibre just eight centimeters wide, you could support all of that force. But now the problem is if you have less than a centimeter of that fibre, it adds another another gram to the tip of your tether. So now you need a thicker fibre to support that additional force. And that would happen all the way to the base, the fibre would need to get thicker and thicker and thicker all the way back to the motor. And if you do the calculations you'll find that basically thirty meters from the tip, the fibre already has to be as wide as the observable universe in order to support all of that force.

This is what I don't understand. A carbon nanotube fibre eight centimeters wide seems to be all right, but if you have less than a centimeter of that fibre, the fibre has to get thicker and thicker so that it is as wide as the observable universe after thirty meters.

Okay - does he mean that an eight centimeter wide carbon nanotude is fine, but if that nanotube fibre is less than a centimeter long, you are in trouble?

Ann

[MargaritaMc]

Where is the quote from, Ann? It sounds something like what he said, but I didn't see a transcript: did you write down what he said? You must be able to do shorthand.

M

[Ann]

Where is the quote from, Ann? It sounds something like what he said, but I didn't see a transcript: did you write down what he said? You must be able to do shorthand.

M

I wrote down what he said. I stopped the tape and played it, and stopped it and played it until I had it all.

Ann

[Chris Peterson]

This is what I don't understand. A carbon nanotube fibre eight centimeters wide seems to be all right, but if you have less than a centimeter of that fibre, the fibre has to get thicker and thicker so that it is as wide as the observable universe after thirty meters.

Okay - does he mean that an eight centimeter wide carbon nanotude is fine, but if that nanotube fibre is less than a centimeter long, you are in trouble?

First, an eight centimeter diameter nanotube fiber is probably a cable made of billions of individual nanotube fibers. That's because a single carbon nanotube fiber wouldn't be all that strong. At the "tube" part of the name implies, these are molecules with cylindrical surfaces. You need to fill the full eight centimeter volume, so you need many fibers.

Otherwise, all he's saying is that while such a cable is theoretically strong enough to hold up to the centripetal force created by a 1 gram body moving very close to c at the end of the line, that disregards the mass of the cable itself, which is many orders of magnitude greater than the 1 gram test mass. At the rotor, the spinning mass consists of the 1 gram body at the end, and thousands of grams of carbon fiber in between. So it takes a very thick fiber at the rotor to support all that.

[Ron-Astro Pharmacist]

Who composed the limerick:
There Was a Young Lady Named Bright... ?
Quote Investigator, December 19, 2013

<<The earliest evidence known to QI appeared in an issue of the London humor magazine “Punch” in 1923.
Initially, the limerick “Relativity” was published without attribution:

• • Relativity.
  There was a young lady named Bright
  Whose speed was far faster than light;
  She set out one day
  In a relative way
  And returned on the previous night.

In 1937 A. H. Reginald Buller wrote a letter to “The Observer” newspaper in London and claimed authorship of the limerick. A. H. Reginald Buller was a Professor of Botany at the University of Manitoba. In April 1927 the “Manitoba Free Press” which is also based in Winnipeg printed a version of the limerick, and this time Buller was credited. Buller discussed the circumstances of its composition:

• As the author of the Relativity limerick perhaps I may be allowed to say that the limerick was made by me about fifteen years ago whilst sitting in the garden of my friend and former colleague, Dr. G. A. Shakespear, Lecturer on Physics at the University of Birmingham. After conversing together on Einstein’s theory, I suggested that we should each try to make a relativity limerick. At the end of about five minutes the limericks were ready and were exchanged, but with nothing more than a trace of mutual admiration.
  
  Buller stated that two years later he attended a scientific meeting, and he recited the limerick to fellow scientists who laughed and applauded. Shortly afterward a reporter for the “Winnipeg Free Press” told him that the work should be submitted to “Punch”:
  
  On arriving at the university I wrote out the limerick and at once sent it off to Punch. Six weeks later I received from the editor a copy of “Punch” with my limerick in it, and an honorarium of a few shillings. The date of publication was December 19, 1923.
  
  Since the relativity limerick was published I have noted that at various times it has been attributed to three bishops and to a well-known American authoress!—Yours etc.,
  
  • A. H. Reginald Buller,
    Emeritus Professor of Botany, University of Manitoba.
    Royal Botanic Gardens, Kew.>>

Second verse – same but much worse…

Next was the fellow those might
‘spite efforts fell in a dark night
His mass was contained
With a horizonal stay
Not even he could get past delight

[Beyond]

I dunno, Ron. I think your assessment of the second verse is about two much's too short

[Ann]

Photo: footage.shutterstock.com

Way back when, many years ago, I read an explanation as to why it is impossible to travel faster than light, or even as fast as light. The explanation involved thinking of acceleration as a series of pushes, like when you give a child's toboggan a push to make it go faster. Imagine, said the person explaining this, that there is no such thing as friction between the toboggan and the snowy ground, and all the energy contained in the push increases the speed of the toboggan. But now imagine that you keep pushing, and the sled is moving faster and faster. Slowly, gradually, more and more of each "energy push" will increase the mass of the child and her vehicle rather than increasing their speed. As you increase the speed, more and more of the added energy goes into increasing the mass rather than the speed, and eventually, as they really approach the speed of light, the child and her sled will become as massive as the universe.

I guess the correct way of putting it is that the inertia of the child and her sled would approach infinity as they approached the speed of light. It is still interesting to think about.

Ann

[Beyond]

So, if you have a kid zipping about at about the speed of light, getting into all sorts of mischief and really deserves a spanking, you would only hurt your hand by hitting that big a mass.

[geckzilla]

How close to the speed of light? The kid is going to vaporize you along with the general vicinity and perhaps a good portion of Earth.

[Chris Peterson]

I guess the correct way of putting it is that the inertia of the child and her sled would approach infinity as they approached the speed of light.

That's a correct way of putting it. I try to avoid using "inertia", since it's not always an idea people get, and too often it's not defined very well.

In the classroom, I just remind students of Newton's Second Law: F = ma. In the world of special relativity, mass increases with velocity, becoming infinite at c. Most people can see what happens to F as m approaches infinity: it too approaches infinity. Of course, since work (energy) is proportional to force when we're moving something, infinite force implies infinite energy.

[neufer]

I guess the correct way of putting it is that the inertia of the child and her sled
would approach infinity as they approached the speed of light.

That's a correct way of putting it. I try to avoid using "inertia", since it's not always an idea people get, and too often it's not defined very well.

In the classroom, I just remind students of Newton's Second Law: F = ma. In the world of special relativity, mass increases with velocity, becoming infinite at c. Most people can see what happens to F as m approaches infinity: it too approaches infinity. Of course, since work (energy) is proportional to force when we're moving something, infinite force implies infinite energy.

One might assume from this that: F = m a = m₀ a or a = F/(m₀)

• where

however, in truth, F = d(mv)/dt = m₀ d(v(v))/dt = ³m₀ a

• or a = F/(³m₀)

At 99% the speed of light little Sally & her sled seem to weight ~356 times what they used to

[Beyond]

Only 356 times heavier at 99% of c ? Is there a whopping big increase then, during that last 1% of c ??

[Chris Peterson]

One might assume from this that: F = m a = m₀ a or a = F/(m₀)

Indeed, if by "one", you mean yourself. But for a typical, lay audience, I think F = ma will be interpreted as F = ma, and most will understand that as mass increases, the force increases as well, and that if the mass becomes infinite, so will the force.

It's not intended as a detailed analysis of special relativity, simply a framing of a special relativity concept using a classical approach, something just a little bit more rigorous than using the word "inertia". It's about seeing a trend, not calculating a value.

[Chris Peterson]

Only 356 times heavier at 99% of c ? Is there a whopping big increase then, during that last 1% of c ??

Yes. All the intuitionally bizarre aspects associated with relativistic velocities are exponential in nature, increasing dramatically as c is approached. That last 1% gets more interesting if you break it up finer: the increase between 99.9999 and 99.99999 is even more impressive!

[rstevenson]

There's a confusion that creeps into discussions about relativistic speed effects that stems from our common usage of the word mass. Mass as we use it, here in our slow-moving Newtonian world, is "rest mass", which is not what physicists mean when they talk about mass increasing with speed. In our Newtonian world "rest mass" and "mass" are one and the same thing, or so close to it that no meaningful distinction can be made. But physicists are talking about "relativistic mass" or "inertial mass", and more particularly about the very real equivalence of mass and energy. Perhaps, in discussions here on a public, mostly non-physicist site, we might better serve the role of public outreach by using the appropriate modifier, as in rest mass or inertial mass, to make clear what we're talking about. And if that then requires a little more explanation, that's all to the good.

Rob

[neufer]

One might assume from this that: F = m a = m₀ a or a = F/(m₀)

Indeed, if by "one", you mean yourself. But for a typical, lay audience, I think F = ma will be interpreted as F = ma, and most will understand that as mass increases, the force increases as well, and that if the mass becomes infinite, so will the force.

It's not intended as a detailed analysis of special relativity, simply a framing of a special relativity concept using a classical approach, something just a little bit more rigorous than using the word "inertia". It's about seeing a trend, not calculating a value.

• Inertia is an extremely important concept for lay people to understand
  
  While F = m a is a bit more rigorous it is dead wrong for a mass changing object!
  
  Rather: F = d(mv)/dt = m d(v)/dt + v d(m)/dt
  [list]F = m a + v d(m)/dt

The second term [v d(m)/dt] is important for both:

• 1) mass losing non relativistic rockets
  2) and mass gaining relativistic sleds

There is no point in teaching relativistic mechanic and avoiding inertia. [/list]
I would teach in order:

• 1) the concept of Newtonian inertia, a la: a = F/m₀
  2) the concept of Einsteinian inertia, a la: a = F/(³m₀)
  
  and never mention: a = F/(m₀) [except in the case of perpendicular forces].

[geckzilla]

That's too much calculus for a lay person. You may as well be accosting them with unwanted Red Bull drinks.

[Chris Peterson]

While F = m a is a bit more rigorous it is dead wrong for a mass changing object!

No, it isn't. It simply isn't perfectly correct- which is generally the case for classical analysis of motion. I think F = ma is the best way to understand inertia, and I think it's the best way for people to gain an intuitive understanding of what happens in the relativistic case. And for most people, an intuitive grasp of a concept is immensely more valuable than an analytical grasp.

[neufer]

That's too much calculus for a lay person. You may as well be accosting them with unwanted Red Bull drinks.

I'm forEVER optimistic about a lay person's ability to grasp physics, calculus & obscure media references from the '50's & '60's:

<<Gilligan's Island is an American sitcom that aired on the CBS network from 1964 to 1967. Four different boats played the part of the S.S. Minnow named in reference to Newton Minow, chairman of the U.S. FCC, who was most famous for describing television as "a vast wasteland".>>

[neufer]

While F = m a is a bit more rigorous it is dead wrong for a mass changing object!

Rather: F = d(mv)/dt = m d(v)/dt + v d(m)/dt
[list]F = m a + v d(m)/dt[/list]

No, it isn't. It simply isn't perfectly correct- which is generally the case for classical analysis of motion. I think F = ma is the best way to understand inertia, and I think it's the best way for people to gain an intuitive understanding of what happens in the relativistic case. And for most people, an intuitive grasp of a concept is immensely more valuable than an analytical grasp.

• In vain, though by their powerful Art they bind
  Volatile Hermes, and call up unbound
  In various shapes old Proteus from the Sea,
  Drain'd through a Limbec to his native form.
  — John Milton, Paradise Lost, III.603–06

http://apod.nasa.gov/apod/ap951104.html
http://en.wikipedia.org/wiki/Proteus_%28moon%29
http://asterisk.apod.com/viewtopic.php? ... 57#p203257

<<According to Homer (Odyssey iv:412), the sandy island of Pharos situated off the coast of the Nile Delta was the home of Proteus, the oracular Old Man of the Sea and herdsman of the sea-beasts. In the Odyssey, Menelaus relates to Telemachus that he had been becalmed here on his journey home from the Trojan War. He learned from Proteus' daughter, Eidothea ("the very image of the Goddess"), that if he could capture her father he could force him to reveal which of the gods he had offended, and how he could propitiate them and return home. Proteus emerged from the sea to sleep among his colony of seals, but Menelaus was successful in holding him, though Proteus took the forms of a lion, a serpent, a leopard, a pig, even of water or a tree. Proteus then answered truthfully, further informing Menelaus that Odysseus was stranded on Calypso's Isle Ogygia.

The German mystical alchemist Heinrich Khunrath wrote of the shape-changing sea-god who, because of his relationship to the sea, is both a symbol of the unconscious as well as the perfection of the Art. In modern times, the Swiss psychologist Carl Jung defined the mythological figure of Proteus as a personification of the unconscious, who, because of his gift of prophecy and shape-changing, has much in common with the central but elusive figure of alchemy, Mercurius.

Shakespeare uses the image of Proteus to establish the character of his great royal villain Richard III in the play Henry VI, Part Three, in which the future usurper boasts:

• I can add colors to the chameleon,
  Change shapes with Proteus for advantages,
  And set the murderous Machiavel to school.

Shakespeare also names one of the main characters of his play The Two Gentlemen of Verona Proteus.

Proteus is the name of the submarine in the original story by Otto Klement and Jay Lewis Bixby, which became the basis for the 1966 film Fantastic Voyage and Isaac Asimov's novelization.

John Barth's novelette "Menelaiad" in Lost in the Funhouse is built around a battle between Proteus and Menelaus. It is told as a multiply-nested frame tale, and the narrators bleed into each other as the battle undermines their identities.

The alien character of Prot in the book trilogy by Gene Brewer and played by Kevin Spacey in the movie K-PAX, like Proteus was said to embody, was a modernized "shape shifter" and magical type of advanced mystical ET who "walked in" to humanoid bodies, and shared wisdom and insights into the human condition.

The crew of the Jupiter 2 in the 1998 film Lost in Space encounter and board a derelict space station named the Proteus.

In the Harry Potter series, Hermione Granger casts a Protean charm (named after Proteus) on galleons (a form of wizarding currency) to inform members of Dumbledore's Army of meetings. When she changes the properties of the original coin, the amendments are reflected on those she has given to other people to display the date.>>

[geckzilla]

We should put you out front to keep the rabble out, Art.

[neufer]

We should put you out front to keep the rabble out, Art.

<<A sphinx (Greek: Σφίγξ) is a mythical creature with the haunches of a lion, the wings of a great bird, and the face of a woman thought of as a guardian often flanking the entrances to temples. She is mythicised as treacherous and merciless. Those who cannot answer her riddle suffer a fate typical in such mythological stories, as they are killed and eaten by this ravenous monster.>>

• But I'm a guy (a sphinctor ) trying to keep the rabble in

[Ron-Astro Pharmacist]

While F = m a is a bit more rigorous it is dead wrong for a mass changing object!

No, it isn't. It simply isn't perfectly correct- which is generally the case for classical analysis of motion. I think F = ma is the best way to understand inertia, and I think it's the best way for people to gain an intuitive understanding of what happens in the relativistic case. And for most people, an intuitive grasp of a concept is immensely more valuable than an analytical grasp.

Who is familiar with the investigation of the math regarding dark matter? If you take Newton’s equation F = ma and, for the sake of understanding, delete one of the variables, say mass, would it make any sense to consider with dark matter F = a ? Or perhaps m equaling a constant that is similar in galaxies with a known regular mass.

I know this is off topic but it came across my mind while reading these threads. After all, isn’t the force of gravity wh we are really missing and one of the main reasons we conclude dark matters existence?