Discussion in 'The Lighter Side' started by Steve Koski, May 18, 2003.

1. ### Steve KoskiGot Insurance?Millennium Member

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Help me here. I can't quite put my finger on this one.

A runner stands at rest next to a 10' long barn. He's holding a 10' long pole. He then backs up and runs towards the barn at .866c.

The farmer standing by his barn says "his pole is only 5' long (due to relativistic effects), so I'm going to shut him in the barn once he gets inside."

From the runner's perspective (which is just as valid as any other non-accelerating frame of reference), he is holding still and the barn is approaching him at .866c, so the barn looks 5' long, but the pole still measures 10' long. He says "The farmer can't trap me in the barn, the pole is longer than the barn."

So what gives?

Thanks,

Koski

2. ### WillardWho, me?

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I think you are confusing the effects of relativity. It is the appearance of these objects that changes - not their actual size.

Of course, if the guy is moving at .866C, and the barn door closes on him, there's gonna be a heck of an explosion!!!

3. ### HAVOCRememberCLMMillennium Member

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It's a trick question...

Travelling at .866c inside the earth's atmosphere will pretty much lead to him being reduced to subatomic particles as the result of a very impressive explosion... probably wiping out the barn and the farmer in the process.

4. ### Steve KoskiGot Insurance?Millennium Member

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Willard,

Try again. The farmer will correctly measure the moving pole at 5' and the stationary barn at 10'. The runner will correctly measure the stationary pole at 10' and the moving barn at 5'. It violates our common sense, but is correct.

HAVOC,

OK, change the particulars to a vacuum with small particles, or however you wish. The apparent paradox remains the same.

Anyone else??

Thanks,

Koski

5. ### gamegod86Male Lesbian

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I think the runner will say "Holy (Moley), that's a fast farmer" and "hey, don't close that door!!!"

6. ### Dennis in MAGet off my lawn

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So basically, he's gonna get squirshed either by the back wall of hte barn or the door slamming him in the side (assumed a sliding door) depending on when he decelerates.

And who makes a 10' barn anyhoo??? What a waste of lumber.

7. ### riddleofsteelPulpa est valeo

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If E=mc2 is correct then an objects energy equals its mass times the spped of light squared when the speed of light is obtained.
Now assuming that an object that has mass can be accelerated to this speed in normal space/time (questionable) then...

The mass of the runner and the pole increases as the speed of light is approached. I would think that in this case no barn door would hold them.

Of course for an object with mass to reach the speed of light within normal space it would have to be contained within a bubble or modified section or normal space.
Given the recent connection between Einstein's theory of relativity and magnetic fields and the possibility that a magnetic field can "stiffen" space-time, which is in effect altering the effects of gravity and mass on space-time,

would it not be possible to create an extremly large magnetic field that in effect "shields" any object within the field from the effects of gravity outside the field. This field would also shield the universe from the gravitational effects of the object. If you could do this, have you not just negated the E=MC^2 law from holding within the bubble? Is this not in essence a "warp" bubble and would it not be possible to move the bubble through space-time at velocities greater than C because the mass within the bubble would be "shielded" from the rest of the universe?
Holy This is what I like, ideas!

That bubble would have to move across the space for itself. Since the mass inside it will have to stay inside the bubble and does not have to move at all, the bubble itself must move. But can the bubble exceed the speed C?

I might be mistaken but doesn't a electromagnetic wave propagate at the speed of light (C)? If one could use that when constructing the bubble one could possibly direct the magnetic field to travel at the speed of C in a specific direction. Since the mass inside the bubble isnt showing to the outer space, and the bubble is a magnetic field (with no mass), the bubble might be able to travel at the speed of light.

However since this process would require MASSIVE amounts of energy. More energy than mankind has produced in its entire history. I guess the runner has to stick to around the 15 to 20 MPH our feet can manage and the question is moot.

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Man, you guys GOTTA get a life! ;f;e;f;e;f

..Joe

9. ### Steve KoskiGot Insurance?Millennium Member

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Puddle,

You are out there my friend. There is no such thing as a pure magnetic wave. Only electromagnetic waves, which travel at c. Your theory of "magnetic waves" altering space/time is a new one on me.

Koski

10. ### Roger C

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Related to the ideas behind gravity waves.

Solution: Since any farmer that can measure the length of a pole moving at him at .866c must be Superman on crack, the runner is SOL.

11. ### HAVOCRememberCLMMillennium Member

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Not sure about the existance of magnetic 'waves', but magnetism and electromagnetic radiation are not the same thing. I'm not even sure how the term electromagnetic came to be used... an electromagnet doesn't create electromagnetic radiation as a primary product.

12. ### riddleofsteelPulpa est valeo

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Seems like folks as learned as NASA believe in magnetic waves...

From a NASA Press Release
July 8, 1999: The high-speed portion of the solar wind achieves its unexpectedly high velocity -- up to 500 miles per second -- by "surfing" magnetic waves in the Sun's outer atmosphere, according to observations made by two spacecraft. For 37 years, solar scientists have been puzzled by the fact that the high-speed solar wind travels twice as fast as predicted by theory. Observations and theoretical analyses have discovered a surprising explanation for this mystery: magnetic waves.

Left: The SOHO Spacecraft.
Right: The Spartan Spacecraft flying free of the Shuttle bay.

The observations were made using instruments aboard NASA's Spartan 201 spacecraft, deployed from the Space Shuttle during the STS-95 mission, and the international Solar and Heliospheric Observatory (SOHO). "The mystery was first presented by the Mariner 2 spacecraft in 1962, the same year as Glenn's first flight," said Dr. Marcia Neugebauer of NASA's Jet Propulsion Laboratory, Pasadena, CA, the co-principal investigator of the solar wind instrument on Mariner 2. "The new observations made by SOHO and by the Spartan 201 mission during Glenn's return to space put us much closer to finally unraveling the mystery of the acceleration of the solar wind."

December 3: Mars Polar Lander nears touchdown

December 2: What next, Leonids?

November 30: Polar Lander Mission Overview

November 30: Learning how to make a clean sweep in space

Left: The solar corona, as seen during an eclipse.

The outermost solar atmosphere, or corona, is an extremely tenuous, electrically charged gas that is seen from Earth only during a total eclipse of the Sun by the moon, when it appears as a shimmering white veil surrounding the black lunar disk. Using Spartan and SOHO, scientists have detected rapidly vibrating magnetic fields within the corona that form magnetic waves that appear to accelerate the solar wind. "These vibrating magnetic waves give solar wind particles a push, just like an ocean wave gives a surfer a ride," said Dr. John Kohl, a senior astrophysicist at the Smithsonian Astrophysical Observatory in Cambridge, MA, and the principal investigator for ultraviolet spectrometers aboard SOHO and the Spartan 201.

The electrical charges of solar wind particles, or ions, force them to spiral around invisible magnetic lines in the corona as they rush into space. When the lines vibrate, as they do in a magnetic wave, the spiraling ions are accelerated out and away from the Sun. The presence of magnetic waves in the corona was inferred by observing the motions of these solar wind ions. "We were quite surprised to find that heavier oxygen ions actually moved faster than lighter hydrogen ions," said Dr. Steven Cranmer of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "The best explanation for this is a magnetic field line that wiggles back and forth in the same amount of time that oxygen ions take to spiral around it. Just as a child riding on a swing moves higher if someone pushes with the right rhythm, the resonant magnetic waves give a boost to the oxygen ions."

Above: This image shows three frames from a QuickTime animation (click the image to view) illustrating how magnetic waves in the Sun's outer atmosphere (corna) accelerate the solar wind. The corona is seen as a feathery yellow ring around the lunar disk during eclipse in the first image, the particles making up the solar wind (red and green) spiral around the magnetic field lines (white lines), accelerating away from the Sun. The spiraling solar wind particles take energy from the magnetic waves, canceling them out as the particles rush into space.

Previous Solar Wind Stories
--------------------------------------------------------------------------------

Up, up, and away to the magnetosphere
"Gentle" puffs of solar wind stir the Northern Lights
Solar wind blows part of Earth's atmosphere into space
NASA/Marshall Astronomy - Tiny bubbles from the sun
Earth weaves its own invisible cloak

Recent SPARTAN Stories
--------------------------------------------------------------------------------

Astronomy goes into orbit with John Glenn
A Tale of Two Mysteries on shuttle Discovery

Recent SOHO Stories
--------------------------------------------------------------------------------

SOHO spies the far side of the Sun
Cool microflares could be solar hot spots

The scientists believe there are magnetic waves in the corona with many different "wiggling periods," or frequencies. These waves accelerate various solar wind particles that spiral around the field lines at different rates. The observations also will help scientists better understand solar regions called coronal holes. "Solar winds from these regions enhance energetic electrons in the Earth's Van Allen radiation belts, which can sometimes affect the electrical systems aboard Earth-orbiting satellites," said Joseph W. Hirman, Chief of the Division for Space Weather Operations at the Space Environment Center operated by the National Oceanic and Atmospheric Administration in Boulder, CO.

Even with this major discovery, there are questions left to answer. "The observations have made it abundantly clear that heavy particles like oxygen 'surf' on the waves, and there is also mounting evidence that waves are responsible for accelerating the hydrogen ions, the most common constituent of the solar wind," Cranmer said. "Other common particles, such as helium, have never been observed in the accelerating part of the corona, and new observations also are needed to refine our understanding of how the waves interact with the solar wind as a whole."

The SOHO mission is sponsored by NASA and the European Space Agency. This research was published in the June 20 edition of the Astrophysical Journal.

13. ### Steve KoskiGot Insurance?Millennium Member

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HAVOC,

A changing magnetic field produces an electric field, and vice versa. Read up on Maxwell. Electric and magnetic fields are virtually inseparable except in totally static cases.

Riddle,

Interesting. 500 miles/sec is a whole lot slower than 186,000 miles/sec (c), .0027c. If you run across any more links with more description I'd love to read them.

Koski

14. ### rcarroll49

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Actually magnetic fields(static or dynamic) don't really exist at all even in permanent magnets. They are a relativistic manifestation of electric fields. Check it out in the latest E&M theory texts.

15. ### Steve KoskiGot Insurance?Millennium Member

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OK, some folks call them magnetic fields. Does the name matter?

Can you explain further? How does relativity fit in?

Koski

16. ### jhfentonEvil Marathoner

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Simultaneity is relative, too.

17. ### rcarroll49

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n

Of course in engineering we still use the classical E&M equations and Maxwell's equations describing Electric and Magnetic Fields. Just a side note in the world of physics trying to develop unified theories, one can show that magnetic fields are relativistic version of E-fields. Take two parallel conductors carrying DC current in opposite directions. The two conductors will be attracted by a "magnetic" force. We see this everyday in electric motors. The electron current in the two wires are not moving anything near the speed of light so how would special relativity come into play? Like this: The moving currents "see" the non-moving positive nuclei in the other wire closer together. Just like your original Barn and stick problem. A current in one wire sees a net positive charge/inch in the other wire. Likewise the other wire's electron current sees a net positive charge/inch in the original wire. Each wire is actually electricaly neutral but relativistically sees a positive charge. Each wire is electrically attracted to each other's Electrons & Positive charges. Because the electron current is moving slow relative to the speed of light, very little distance contraction between nuclei is seen in the other wire. Like when you drive through a tunnel with your Dodge Viper you will see very little contraction of the tunnel's length, but there will be some relative to you in the Viper. However if you have millions of electrons flowing through each wire/sec. One amp = one coulomb/sec = 6.24 quintillion electrons/sec. You will have in the aggragate a lot of electrical force being generated between the two wires. This force is at right angles to the flow of current in the wires. It is interresting that Einstein's special relativity acutally can explain things not traveling close to the speed of light. Magnetism is a real world example of the original barn and rod problem.

18. ### Steve KoskiGot Insurance?Millennium Member

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rcarrol,

Kool. Never heard that version of it. Nice explanation for us ME types.

Koski

19. ### Steve KoskiGot Insurance?Millennium Member

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It think that's where the solution to the paradox lies, but I'm not exactly sure how.

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