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epoisses (Chemical) (OP)
19 Aug 05 11:00
What about a thread on the greatest fundamental physical misconceptions. They can be historical or present-day. I'll kick off with a real life example.

At home we have a jug with a water filter because the tap water is disgusting. We usually let it in the sink after filling it because filtering is rather slow. My sister-in-law who visited us the other day asked me if there was any technical reason why I put the filter in the sink (which is about 20 cm deep): "Is that to make it filter faster?". I tried to explain the special theory of relativity of height, but it didn't make it easier for her. She finally found peace when I explained it was just laziness to leave it in the sink. (She's not unintelligent otherwise although I must admit she often buys lottery tickets.)

Can anybody top that?
TheTick (Mechanical)
19 Aug 05 11:50
Perhaps the additional gravitational force resulting from extra inches toward the center of the earth increase performance?
JAE (Structural)
19 Aug 05 12:21
The strapless bra doesn't use anti-gravity paint.
icelad (Civil/Environmental)
19 Aug 05 13:18
Try explaining to someone that air is a fluid, glass is a liquid and that something level is not flat.

On the explaining to someone part, the best way I ve heard to explain the 3 laws of thermodynamics:

1  You cant win
2  You cant break even
3  You cant even get out of the game

JAE (Structural)
19 Aug 05 13:30
I once read an artlicle about a physics professor (somewhere out on the west coast - can't remember his name) who was doing lots of research at a molecular level.  He claimed in the article that the long held concept of atoms being little pieces of "matter", just like a little solar system wasn't correct - I specifically remember him saying something like "I can show you a proton that is 10 ft. in diameter"....basically saying that these atomic elements were waves, and not particles....but this is waaaay over this little structural guy's head.
gaufridus (Mechanical)
19 Aug 05 14:22
My parents always called me 'the greatest physical misconception'
25362 (Chemical)
19 Aug 05 14:23

The caloric theory of heat. It is a very strange substance this caloric, it has no weight but nonetheless it occupies space since things tend to expand as they heat up and shrink as they cool.

It was, I believe, Benjamin Thompson, Count Rumford who, by the end of the 18th century, ended the scientific reign of this misterious caloric fluid with the help of several cannons...

The caloric theory of heat has long since passed into the history of quaint scientific ideas, but it left us with the calorie as a unit of energy... that is, until the arrival of the joule.

zdas04 (Mechanical)
19 Aug 05 21:16
I like the conspiricy theory that "someone" has invented a car that "uses water as it's only fuel, but that big oil and big auto have squelched it (often with the added twist that they had the inventor killed)".

When you try to explain that you need a definition of "runs on water" you don't get far.  If you try to provide a possible method (e.g., solar panels, batteries, electrolisis, fuel cell and/or burning hydrogen) and the reasons that you would be violating most of the thermodynamic laws that icelad so elequantly laid out for us they glaze over and accuse you of being part of the conspiricy.

Sometimes the theory comes across as a "carborator" that will allow water to be "burned".  If you point out that water is occasionally used as a fire suppressant they come back with "the carborator fixes that".

TheTick (Mechanical)
19 Aug 05 21:56
How about "Hot water freezes fater than cold water."?

There's no such thing as thermal inertia!
GregLocock (Automotive)
19 Aug 05 22:12

Ice cream manufacturers put their money where their mouths are and deliberately freeze warm milk to get it to freeze faster.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

quark (Mechanical)
20 Aug 05 2:20
The Mpemba effect was discussed in thread164-57348

Pressing down a hose at the edge to get more flowrate, or to fill a tub faster.

Perpetual motion machines

Invisibility(which is rediculed by the fact that invisible person becomes blind)

rhodie (Industrial)
20 Aug 05 21:29

How about the one where pushing the button on the elevator repeatedly helps get it to me faster?
IRstuff (Aerospace)
20 Aug 05 21:51
Don't know about that, but pushing the floor buttons after someone leaves the car usually speeds up the door closing.


JimCasey (Mechanical)
21 Aug 05 9:02
Pushing the elevator buttons repeatedly to speed up the elevator is calles "elacceleration"

I don't know what you call pushing the button repeatedly for the street crossing light.  
zeitghost (Computer)
21 Aug 05 10:19

It's probably not connected to much...
TheTick (Mechanical)
21 Aug 05 11:07
I'll have to back off on the water freezing thing.  One day I'll have to do my own experiments.
casseopeia (Structural)
21 Aug 05 16:16
Hey JAE, you might be thinking of Brian Green(e)?  not sure of the spelling.

I am currently slogging through his latest book, "The Fabric of the Cosmos".  Very difficult material for me. I think I read about a paragraph and a half each night.

I'll give just a few of the concepts, according to what my pea brain has interpreted.

1. All matter is made of virbating strings.  
2.  The particles of matter do not have a definite spin or location, just a set of probabilities.  You can NEVER know, nor measure these characteristics.  The very act of measuring automatically forces the particle to 'chose' the characteristic you wish to measure.
3.  There is no 'space'.  The concept of space is a mechanism for measuring the distance between matter.  Remove all the matter and space does not exist.
4.  There is no universal mesurement standard for time and space.  It is dependent on the observers relative position, acceleration, place in time, etc.  Hence, there is no universal truth.

I would highly recommend hearing him lecture if you can.  I always leave understanding the concepts at the time, until some asks me to explain it.

"If you are going to walk on thin ice, you might as well dance!"

JAE (Structural)
21 Aug 05 23:33
Interesting - but on your item 4 - if there's no universal truth, then, well, then there's no universal truth to item 4 is there? a self-defeating statement.
MikeyP (Aerospace)
22 Aug 05 4:37
A popular misconception that I come across all the time is that heavier objects fall faster than lighter ones. The reason is that 99% of the time it is true in everyday experience, due to aerodynamic effects.


Dr Michael F Platten

DrillerNic (Petroleum)
22 Aug 05 7:38
Linked to ZDAS's post about Big Oil quashing the water fueled car, there's the variation that Big Oil have patented a water buring car/ electric car/ highly fuel efficient car, again to keep the invention from the world.

Of course a patent, is, by definition, a public document, and only runs for a limited amount of time....
TheTick (Mechanical)
22 Aug 05 9:32
It always surprises me to see how many people (engineers, even) think there is a moment of "hang time" before a dropped object begins to fall.  Too many "Road Runner" cartoons, I guess.
bandraoi (Civil/Environmental)
22 Aug 05 10:43
"Hot water freezes fater than cold water."?

Do freezers ramp up their power when the temperature goes past a certain point and work harder to bring their temperature back down?
If that was the case with some freezer designs then it might have the side effect that a glass of hot water would freeze more quickly than a glass of cold water.
IRstuff (Aerospace)
22 Aug 05 10:47
Read the link.  The phenomenon has been documented for over 2000 yrs.  


dford (Mechanical)
22 Aug 05 12:16
It is common for people to think that vacuum does work and that "cold" flows toward warm.

GregLocock (Automotive)
22 Aug 05 21:37
Just an idle question - could you not explain every facet of thermodynamics by assuming that coolth exists rather than warmth?

I must confess I find temperature a fairly confusing concept at the best of times (cue IRstuff's lecture on freezing windscreens at night when the air temperatureis above freezing, and why a solar furnace can't be hotter than the sun)


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

flamby (Structural)
23 Aug 05 2:32
What is the relative speed if I move towards you and you come forward to me, both of us at 10mph? And what if the speed is that of light?


TheTick (Mechanical)
23 Aug 05 8:51
I used to visualize temperature as the thermal equivalent of pressure.  Heat "deflates" towards cool.  To make something cooler requires a "heat pump" to create a "thermal vacuum".

A bit pedantic, but it helped me put a picture to many concepts.
icelad (Civil/Environmental)
23 Aug 05 9:46
It helps me to remember the ultimate villain, entropy.  It takes more energy to put the gasoline together then the energy released by combustion.  Thus I remember that all systems will try to move toward a less energetic state, i.e. hot will try to move to cold. (Of course, opening the refrigerator door seems to make a lie of that as you feel the cool air spill out into the warmer room)

Similar thought.  If I was standing there watching you approach at the speed of light, would you not suddenly appear and  would seem that you would recede away from me as the images from farther away came to me. (The image of you at 0 feet would get there first, then 1 foot, 2 foot…100 yards, etc.  Even though the farther images left sooner they could not outrace you to form an image on my eye.)

drawoh (Mechanical)
23 Aug 05 14:03

   Regarding glass as a liquid, check out...

   They end up by not being sure exactly what a solid is.  A lot of claims about slow flow of glass are not accurate.

icelad (Civil/Environmental)
23 Aug 05 14:39
Very (super) cool,  It was just something I had been taught back in the early 70s
Thanks for the heads up
swall (Materials)
23 Aug 05 16:39
Wind chill--I hear people worry about not having enough antifreeze in their radiator if the wind chill will be minus 20F even though the temperature remains above 32F.
swall (Materials)
23 Aug 05 16:47
Oops. Meant to say 20F, not minus 20F.
GregLocock (Automotive)
23 Aug 05 22:28
Wind chill is a good one - I vaguely remember it was an experiment involving fit people standing around in the Antarctic and saying how cold they felt.

Oh we used to have a good one on the engine forum - ram air intakes. If you had a really big ram air intake funnelling down to a small throat then you'd get some huge compression wouldn't you?


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

rb1957 (Aerospace)
26 Aug 05 8:36
in canada, wind chill is real (trust me) ...
but what many drivers do (particularly truck drivers) is they cover up most of the radiator ('cause they don't need the evaporative cooling)
PBroad (Mining)
26 Aug 05 10:02
epoisses, try the obvious: You leave the jug in the sink as a safety measure, if it gets knocked over you don't have a wet floor!
zdas04 (Mechanical)
27 Aug 05 10:16
Wind chill is real, no doubt about it, it is the effective rate of heat transfer.  When the wind is blowing hard on a day that is near (but above) freezing, your body will give up heat at a rate that is the same as the rate on a much colder day, but if you die your body will not freeze.

If the temperature is below freezing, the wind chill will accelerate the rate at which something freezes.  Since it is below freezing much of the year in Canada (I've heard August through June, but that might have been an exaggeration), blocking the air flow has the effect of slowing the rate of heat transfer.

TheTick (Mechanical)
27 Aug 05 10:23
Still, as far as cars and wind chill go...

In a car that is not running, the coolant will not get colder than the ambient air temperature, regardless of wind chill.
GregLocock (Automotive)
27 Aug 05 19:14
Sorry, that was my point. The 'calibration' of the wind chill charts you normally see were produced by Antarctic explorers standing around outside in their knickers saying "gosh, it's mighty damn chilly this morning".

As soon as you add clothing, or long term exposure, or change the fitness level or the calorie intake of the subjects, you'll get different curves.

I vaguely remember that people who live in the tropics can die of hypothermia in temperatures that we'd regard as perfectly survivable.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

hyposmurf (Electrical)
1 Sep 05 13:23
1.-A bigger pipe from a elevated tank , give more pressure than a smaller one.

2.-A pump can suck far below 33 fT or 10.033 meter.
3.-Why to worry about vaccum ? , if it is only 1 Atmosphere pressure: this vessel shall resist it, an oil 205 Gl drum.

4.-If you close the output in a centrifugal pum, pressure will burst it.

And keep coming .....

25362 (Chemical)
2 Sep 05 3:00

When dividing approximate physical quantities expressed in whole numbers, the larger the number of digits to the right of the decimal point, the more accurate the answer.

strokersix (Mechanical)
2 Sep 05 13:09
hyposmurf's sucking pump reminded me of one I encountered recently.  A co-worker insisted that a hydraulic cylinder with the rod side open to atmosphere and piston side closed, full of oil, would hold significant tensile load.  I tried to explain that the maximum load would equal one atmosphere pressure on the rod side and more than that would draw a vacuum space on the piston side.  I don't think he believes it to this day.
PBroad (Mining)
2 Sep 05 13:39
Perhaps the greatest physical misconception is that USA has the engineers and resources to combat a force 4 hurricane.  
jbel (Mechanical)
4 Sep 05 7:19

Quote (PBroad):

Perhaps the greatest physical misconception is that USA has the engineers and resources to combat a force 4 hurricane.   

It's not a question of if you have them, it's how you implement their usage.
TheTick (Mechanical)
4 Sep 05 9:26
Sometimes nature wins, and nothing can be done or implemented) about it.
PBroad (Mining)
4 Sep 05 11:27
Jbel is right others less so.

The US has some excellent LCACs that would have resolved the problems in New Orleans much faster however the USS Kearsarge and USS Harper's Ferry (the mother Ships) are deployed in the Gulf.  The best comment I have heard is "A man-made levee will always collapse from lack of maintenance and logical thinking".

The levees were 16-17ft but a full 4 ft lower at the points that collapsed, eroded from the bottom.  Why have a rescue centre below water level?  Police cars and other emergency vehicles were some of the first to be lost, and all this after an excellent "huricane pam" exercise in July 04 that predicded all the experienced problems.

Most of the recomendations made in 1993 (Galloway report)have not been implements.  Many of the levees have not been repaired since 1965. 1,900 sq miles of protective coastline have been lost since 1930, and lack of dredging has resulted in the Mississippi flowing on an "aquaduct" through the city.

The U.S. Army Corps of Engineers requested $27 million for this fiscal year to pay for hurricane protection projects just around Lake Pontchartrain. The Bush administration countered with $3.9 million, and Congress eventually provided $5.7 million, according to figures provided by the office of U.S. Sen. Mary Landrieu (D-La.).

Just to increase the levees by 10 ft will require at lease three times the volume of fill currently used as the levee has a very narrow base and just one wall, no double barrier as used in military fortifications.  Then there are the permitted chemical plants built below sea level that were just accidents waining to happen!!!!
Qshake (Structural)
4 Sep 05 14:45
On that anti-intuitive thought of cool air rushing from the fridge as you open it; suppose it was the warm air rushing into the cooler environ that pushed the cool air out and onto your skin......that would be consistent with the heat sink theory....wouldn't it?


Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

rmw (Mechanical)
4 Sep 05 23:33
OK, I have a question.

On modern juke boxes, (they play CD's instead of records) there is a transparent tube of colored fluid with bubbles in it, but instead of the bubbles rising, they are entering at the top of the tubes and exiting at the bottom.

Not only do the bubbles go in a direction that is counterintuitive, they get larger as they approach the bottom instead of smaller as one would expect them to do due to the increase in static head.

I have been in the presence of these machines with many engineers, most of whom are smarter than me, and no one has offered a plausable explanation of what we are seeing.

Anyone got the answer?

rhodie (Industrial)
5 Sep 05 0:21

CO2 plus surfactant are an oft' attributed culprit of sinking bubbles, but a slightly different effect describes the sinking bubbles in Guinness Draught:

I've never noticed the newer jukebox bubble light traveling the wrong way...  maybe a vaccum force is involved?
zeusfaber (Military)
5 Sep 05 9:19
"Bubbles" made from a clear, denser liquid - and perhaps some change to the tube geometry to create an illusion of expansion?

icelad (Civil/Environmental)
5 Sep 05 10:12
Is the cooler air not denser then the warm air that it displaces, which causes the flow out into the warmer room?
rmw (Mechanical)
5 Sep 05 10:35
The tube geometry is consistent throughout its length (visual observation, I haven't put a micrometer on it) and the bubbles' size changes as the bubbles (spaced about 6" apart) travel from the top of the juke box to the bottom of the jukebox.  Can't see how that would be an optical dillusion.  But I am open to answers.

Intuitively, one would think that if the liquid was flowing from high to low, that as the pressure dropped along the length, the bubbles should grow in size.  What is observed is just the opposite.

Many engineers, and some of them even good ones, have been stumped.  I have yet to have one propose a solution, though.


PS: this brand of jukebox is very common in the USA, so if anyone is out enjoying a bite at an eatery that has one, go observe the phenominon.
MikeHalloran (Mechanical)
5 Sep 05 17:05
One particular Freon used for cleaning refrigeration systems is water-white, immiscible with water, and (very dense) liquid at room temperature.  A switching valve could introduce 'bubbles' of it into a flowing stream of water.

I can't explain the size change.

Mike Halloran
Pembroke Pines, FL, USA

GregLocock (Automotive)
5 Sep 05 18:58
Suppose the tube were tapered and yet ground so as to magnify the image towards the bottom?


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

Qshake (Structural)
5 Sep 05 19:19
icelad - my primitive science background would answer yes to your proposition - the cooler air is denser than the warm air displaced.  

I really don't know the answer but just posed a thought.  Interesting item.


Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

CostasV (Mechanical)
6 Sep 05 6:57
You can see (some of) the obsolete scientific theories at the

epoisses (Chemical) (OP)
6 Sep 05 10:39
The "Rain follows the plow" theory is extremely interesting in the light of another thread in the Where is Engineering going forum.......
Tobalcane (Mechanical)
8 Sep 05 16:36
One misconception that I can think about is the misconception that shapes (2D) with the same perimeter would have the same area.  This is not correct.  If you have a square that is 1in X 1in the perimeter would be 4in and the area is 1in^2.  If we had a circle that had a perimeter (circumference) of 4in, the area would be 1.273in^2.  Same perimeter different areas, I don’t know why but that still amazes me.  Even if you go to a rectangle, say a 0.5in x 1.5in the perimeter would be 4in and the area is 0.75 in^2.

Go Mechanical Engineering

IRstuff (Aerospace)
8 Sep 05 18:36
Goes along with why bubbles want to be spherical


MikeyP (Aerospace)
8 Sep 05 19:41
Here's a good one. I think it was Wittgenstein who came up with it. It is so simple that if you think about it analytically for just a second, you will see the answer. Try thinking about it intuitively instead.

Put a grapefruit (~5 cm radius) on the floor. Take a piece of string and wrap it around the "equator" of the grapefruit and tie it tight. Now remove the string and cut the loop. Then add EXACTLY 2 metres of string to the cut loop and re-tie it into a new, larger loop. Form this new loop into a circle and place the grapefruit at its centre. The gap between the grapefruit and the string will be big enough for you to stand in (about 30 cm or so).

Here is the clever bit. Repeat the process but instead of a grapefruit use the whole earth. Tie the string tight around the equator (assuming a flat surface), cut the loop, add 2 m, re-tie and re-centre.

How big is the gap now? Could you slide an atom through it? could you perhaps slide a human hair through it?

Highlight below for the answer


The gap is still about 30 cm. The relationship between radius and circumference is a linear one (r = c/(2pi)) so adding 2 m to the circumference of any circle always increases the radius by 1/pi metres.


Dr Michael F Platten

IRstuff (Aerospace)
8 Sep 05 22:35
at least a FEW atoms


25362 (Chemical)
9 Sep 05 0:43

It appears that the "new" radius will still be longer than the original by 1m/π, namely the gap would still be ~0.3 m. Am I right ?
GregLocock (Automotive)
9 Sep 05 1:15
I guessed the right answer, based on a long summer holding a surveyor's tape - the extra length you get by eliminating the catenary is very small.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

IRstuff (Aerospace)
9 Sep 05 11:59



IRstuff (Aerospace)
9 Sep 05 12:00
Sorry, haven't had coffee yet.


plasgears (Mechanical)
13 Sep 05 12:52
One common misconception is to set the air conditioning in a space to some lower temp to cool down the space faster. The only thing you accomplish is higher energy bills and a space that is too cool and too dry. I've seen some otherwise smart people do this in public places. I coach them to 'set it and forget it.'

Another misconception is warming up a car in the driveway. It warms up faster as you drive away at moderate speed. It also plays havoc with mileage.
zeitghost (Computer)
14 Sep 05 4:15
That the earth is flat?

And supported by an elephant?
Tobalcane (Mechanical)
14 Sep 05 10:51
Sometimes I wonder how the masses react when they hear the breaking news of an idea being debunked.  Things like the earth being flat or the earth was the center of the universe.  When Galileo try to prove that the earth was not the center of the universe, there was great opposition to a point that he was punished for the idea.

Just thinking out load…

Go Mechanical Engineering

minerk (Mechanical)
14 Sep 05 12:09
I've run into a lot of folks that are convinced that an air receiver or a water tank must have a separate inlet and outlet.

Another one is that filling a tank from the top is "easier" (requires less head from the pump) than filling it from the bottom.
whyun (Structural)
14 Sep 05 12:24
Theory of Evolution as seen by believers of Intelligent Design
IRstuff (Aerospace)
14 Sep 05 16:14

There are millions who haven't been convinced that geocentrism has been debunked yet:

Someone can still claim the prize offered in the last link


zeitghost (Computer)
15 Sep 05 4:39

You mean there really is an elephant?
Maui (Materials)
15 Sep 05 15:48
25362, yes, you are correct. The radius of the original object is irrelevant - the gap remains the same at about 0.32 meters.


Constants aren't; variables won't.

rb1957 (Aerospace)
16 Sep 05 10:41
how life being fair ? ...

sorry, that's a metaphysical mythconception
rb1957 (Aerospace)
16 Sep 05 10:49
geo-centrism ... we (being on the earth) cannot distinguish between the earth rotating around the sun, or the sun rotating around the earth ... but won't a satellite have a sufficient perspective ? ... maybe a pair of satellites (one orbiting the earth, one orbiting the sun) distance measuring between them, angle measuring to a datum star
CSLufkin (Mechanical)
16 Sep 05 10:54
RB, I dont think the $1000 prize money will cover the satelites though!!
rb1957 (Aerospace)
16 Sep 05 10:59
no, but think of the peace of mind (apart from the conspiracy paranoids)
Zoobie (Chemical)
16 Sep 05 12:34
My physics may be a little rusty but what would using a datum star prove.  Isn't that just using another frame of reference (just like using a position on the earth or on the sun or anywhere in between)?  From that point of view you may measure the movements and determine from your frame of reference that the earth is orbiting the sun.  Well what if in fact the star that you are measuring from is actually orbiting the earth.  I am definitely not a geo-centrist but it seems to me that you can probably pick any point in space and call it the center of the universe and based on today's physics and math, make it work...or at least make it difficult for anyone else to refute.
rb1957 (Aerospace)
16 Sep 05 12:53
if you measured the angle between the satellite, the sun and polaris, and you know you are orbiting the earth (radar distance measurement) you'd be able to determine your position in space.

i've thought a little more about this (slow day !).  geo-stationary satellites orbit with a period of 24 hrs.  if the sun is orbiting the earth with a period of 24 hrs, it would be station keeping with satellite (it would have a constant bearing, either in the sun or out of it).  i'm willing to bet that it would sense the sun only 1/2 the time.
minerk (Mechanical)
16 Sep 05 14:23
rb1957's comment got me thinking...does the earth rotate in the geocentric model?  If not, wouldn't that mean that geo-stationary satellites are standing still in space?  I suppose one explanation could be that the earth rotates at one speed, while the sun orbits at a different speed, resulting in the 24 hr day.  Of course that would mean that all calculations relating to the altitude and velocity of geo-stationary satellites are wayyyy off, but I'm sure the geocentrists have a way of explaining that away as well.
rb1957 (Aerospace)
16 Sep 05 14:28
i think they base their claim on the bible saying that the earth is stationary ...
minerk (Mechanical)
16 Sep 05 14:35
Wouldn't it then be blasphemous (sp) to claim that man-made satellites also stand still in space while the universe rotates 'round?  
epoisses (Chemical) (OP)
19 Sep 05 10:32
This bunch of catholics has not understood how science works. There is no such thing as "proving" a hypothesis, one can only falsify wrong hypotheses. They would not award $1000 if we only managed to falsify their geocentrism. Somewhere down the article it says that the award is really about: "Can it be proven, by direct and irrefutable scientific evidence, that the Heliocentric system is the ONLY viable system to understand the universe." - Well of course not, as the author wrote just above that, mathematicians are so smart they can model the universe with the earth of, why not, Jupiter as the middle if they felt like. But why would they develop such an ugly, unnecessarily complicated model?

I find it unconceivable that, 5 centuries after the triumph of Copernicus' free intelligent mind over the retarded ideas imposed by the church, some people still write such kind of articles.

Anyway. Can't full moon, new moon, lunar eclipse and solar eclipse falsify geocentrism already? Or does God just hold his hand in front of it to test us...?
rb1957 (Aerospace)
19 Sep 05 11:03
i think they have a model of a geo-centric solar system, with the moon and the sun orbiting the earth, and everything else orbiting the sun.

i think they can complicate their model "absurdum" to match the visual record.  yes, it results in a very complex model but i don't think science is well served by rubbishing their claims ... i'm not saying that we here have rubbished them, but rather the scientific community in general.  i also think that science is not denigrated by proving these models wrong, that this is not "beneath responsible science".

i was thinking that today we can measure the distance to the planets and as the two models (geo- and helio-centric) have very different predictions about the distance between the planets.  but then i'd expect them to claim that the "ether" affects laser light in ways we cannot understand.
zeitghost (Computer)
19 Sep 05 11:52


Music of the spheres comes next...

As in "la la la what a load of testicles..."?
mechj (Mechanical)
29 Sep 05 17:58
I heard somebody today refer the "speed" of gravity.  In the context of interstellar space travel.  It was stated that, and I am quoting this, that

"When we have computers that can conquer the speed of gravity we can travel anywhere in the universe because time stops."  

Anyone no what the speed of gravity is?

"Education is what remains after one has forgotten everything he learned in school."  Albert Einstein

IRstuff (Aerospace)
29 Sep 05 18:17
Does that matter?  I'm more curious about "time stops."


GregLocock (Automotive)
29 Sep 05 23:00
/If/ gravity waves are real then they will have a wavespeed associated with them. Probably.

There are several experiments running to detect gravity waves, obviously non have succeeded yet.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

quark (Mechanical)
30 Sep 05 0:41
It is already known fact that the gravitational force is inversely proportional to the square of the distance between two bodies and product of their masses. How fast this change occurs incase of change in the distance between two bodies or masses gives a clue about the speed of gravity. With the tangible time scales available to us, so far, this seems to be instantaneous. It is even thought that gravity propagates at speeds much greater than that of light. Here is a link to one such fascinated idea,

This link is just to give you an idea about what speed of gravity is. Nothing is guaranteed for the actual technical content. Infact, maximum members of a physics forum, in which I regularly participate, ridiculed this idea, when I posted this link there.

epoisses (Chemical) (OP)
30 Sep 05 4:51
Well this may or may not be a misconception, we'll know as soon as someone manages to falsify the idea (which is not the same as ridiculising it).
GregLocock (Automotive)
30 Sep 05 9:10
My very vague view is that gravity waves must be very fast, so we probably don't have a good model for them. I'm always amused by how flaky cutting edge physics is, but that's OK, we'll have a working warp drive while the physicists are still arguing about the maths. I hope.


Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RDK (Civil/Environmental)
30 Sep 05 9:56
It doesn’t take an engineer to know that whenever someone starts a sentence with “It doesn’t take an engineer to know” that the remainder of the sentence usually has nothing to do with engineering and is wrong.

Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

zdas04 (Mechanical)
30 Sep 05 10:46
Same with "it's a known fact".

quark (Mechanical)
30 Sep 05 12:56
The correction in my post should be 'the gravitational force is inversely proportional to the square of the distance and directly proportional to the product of masses'.

With that, "it is a known fact" actually relates to the universal law of gravitation only or atleast I thought so. I provided the link to give mechj an idea about speed of gravity and not for its numerical value.

Anyhow, I did enjoy the excellent contradiction about saying truth. It is worth remembering.

EnglishMuffin (Mechanical)
1 Oct 05 17:02
quark : VanFlandern is generally regarded as a crank in mainstream physics circles. My understanding is that in General Relativity, gravity waves and gravity both travel at the speed of light, whereas in Newtonian physics, you have to assume that gravity travels at infinite speed, to avoid aberration effects which are known not to occur. In general relativity, for purely circular orbits, the aberration effect which would be produced by assuming a finite speed of gravity is exactly cancelled by the space curvature effect. For elliptical orbits, (which all the planets have) this does not quite happen, so the perihelion of the orbit advances slightly. It is interesting to note that Gerber got the correct answer for the advance of Mercury's perihelion considerably before Einstein did, just by assuming gravity travelled at the speed of light, but Einstein said he had made a number of mistakes and his analysis was "completely wrong". But somehow, Gerber got the right formula, and some have speculated that Einstein mucked about with his own theory until it was consistent with Gerber's result. Gerber was only a humble schoolmaster, and regarded by the mainstream as a bit of an amateur, so who knows - maybe VanFlandern has got something. But personally, I think the odds are against it.
jmw (Industrial)
3 Oct 05 8:46
Another misconception:
the internet is free, uncensored and unregulated -
and that it should be.
"High minded" people don't ever seem to allow for human nature.


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