How can we determine how fast an object is moving if we do not know how fast we are moving? We could be traveling at the speed of light and not know it.

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Why are apples not bananas since they are both fruit?

If you do things right, people won't be sure you've done anything at all.

Just some little facts that might help....

"...galaxies experience neutral attractions on one other. Due to relativity, the speed of the Milky Way varies when compared with different objects in space. For example... the Milky Way and Andromeda galaxy are approaching each other with a speed of about 130 km/s, however the collision of these two galaxies will not occur for about 5 billion years. Another result... was that our galaxy and neighbors are moving at 600 km/s in the direction of the constellation Hydra. Finally... the Milky Way moves through space within the cluster of galaxies it is a member of, and this cluster in turn moves through space towards yet another larger cluster of galaxies off in the direction of the constellation Virgo. This speed is approximately 300 km/s. Therefore, the speed of the Milky Way galaxy is not a single number, its value is relative to the speed of other objects" - Patricia Kong 1999

The motion of galaxies is determined from an apparent change in the color of light they emit. There are gaps within the spectra of the light emerging from every galaxy. These gaps, called absorption lines, are not located in the spectra at random. The patterns in the missing wavelengths tell us something about the elements present in the stars. In a sense, spectra are like fingerprints. Each element has its own specific set of absorption lines. When a star or group of stars (which is what a galaxy is) are moving relative to us on earth, these elemental fingerprints get shifted from their usual location in the spectra. When a galaxy is moving towards us, these fingerprints get shifted toward the blue end of the spectrum and when a galaxy is moving away from us, they get shifted toward the red end. The amount of shift can be used to determine speed. The greater the shift, the faster the galaxy is moving relative to us on earth.

In 1987, a group of seven astronomers uncovered this coordinated motion of the Milky Way and our several million nearest galactic neighbors -- Alan Dressler, Sandra Moore Faber, Donald Lynden-Bell, Roberto Terlevich, Roger Davies, Gary Wegner and David Burstein. Their results were so astounding they acquired the equally astounding nickname of "The Seven Samurai" (the name of a classic Japanese Samurai movie that spawned the classic American Western movie "The Magnificent Seven"). The place towards which we all appear headed was originally called the New Supergalactic Center or the Very Massive Object until one of the discoverers, Alan Dressler, decided they needed a catchier name and came up with "The Great Attractor".

The mass of the Great Attractor truly is great. Whereas our galaxy contains the equivalent of (10 to the 11th power) solar masses, the Great attractor is estimated to be on the scale of (10 to the 17th power) solar masses; a million times heavier than the Milky Way. If the Milky Way were a piece of gravel, the Great Attractor would be a truck. It's attraction is so strong that we are being sucked into it at the rate of 600 km/s. In comparison, the earth moves around the sun at the relatively pokey rate of 30 km/s and rockets escaping the earth's gravitational pull barely move at 11 km/s.

The Great Attractor is something on the order of 150 million light years from earth. One light year is the distance a ray of light would travel in the vacuum of space in one year -- about 1013 km. At the rate stated, we should arrive at the center of the Great Attractor in something like 15 billion years. Those of you who can't wait will be pleased to know that this is the upper limit on the estimated time of arrival. Since forces accelerate objects we will surely arrive there a few billion years earlier.


...alot of info.... but that hardly scratches the surface...

Arramon

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. ..-={A}=-.. .

Very interested to read about "the great attractor". I was just about to post a question which is partially answered by that notion. I was trying to think how I'd describe red shift etc... so you have saved me a lot of time.

My question (now incorporating the great attractor) is:

If our galaxy - along with everything else, is headed towards the great attractor - are there any objects/galaxies which can be detected coming towards it from "the other side".

Imagine this in two dimensions:
the great attractor is in the centre of an imaginary bicycle wheel (a really large one obviously)
galaxies are travelling towards the centre - down the spokes
so some galaxies from the other side of the hub would be travelling towards us

So are objects converging? :huh: – like in the bicycle wheel
Or diverging? :unsure: – everything moving further away from everything else (which I thought red shift observations had concluded was the case)

I appreciate that the answer may lie with relativity and the expansion of space etc so the answer may be “neither”

But

Can the observations you mentioned by "the seven samurai" detect any convergence or divergence?

Is there only one attractor in the universe?

Questions, questions, so many questions :blink:

Any thoughts?

All velocities can only be measured relative to something. To answer the question, we can only say with any certainty that one object is moving at a speed of x relative to another object. One galaxy to another, an asteroid to a planet, one car to another car.
There is no "true speed", all speeds are relative.

... I guess that means that speed isn't a fundamental quantity of physics!!?? *gasp*

I hope that helps or at least confuses the subject a little more.

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and ... I'd never heard of this Great Attractor thingy! If everything is moving towards it .. is it moving anywhere?? I know Newton (among others) was a proponent of there being a place in the universe that was actually at rest but thought that hypothesis had been diproven?

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Since speed is relative and time is connected to speed. What is our perception of time compared to?

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Why are apples not bananas since they are both fruit?

If you do things right, people won't be sure you've done anything at all.

The Milky Way moves through space within the cluster of galaxies it is a member, and this cluster in turn moves through space towards yet another larger cluster of galaxies off in the direction of the constellation Virgo. The total speed is about 300 kilometers per second or so...

Our time is probably most related to the speed of our own galaxy, the current rotation of it around it's center, its black hole (being a million times the mass of our sun) & tightly grouped stars and remnants of other stars, and the other clusters being tugged around within it that add drag to the whole, and of those small clusters or gobbled galaxies that have their own rotation, but are still turning with the rest of the Milky Way group...

The Time we clock today, is to the rhythm of our current location in our galaxy...
the locations of the others suns and masses around us... it'll take some few million years times 10 for a complete rotation, so we'll keep this Time for awhile...

But Time could be faster or slower depending on your location... distance plays a factor as well...
Being closer to the galactic center may make Time faster, and being farther away the oppostie... and ebing WITHIN the galactic center may stop Time altogether and make it something else... your Space may switch with your Time, and vice versa, making your Time a whole new meaning and instance... while your space, or mass, becomes entwined with a whole new complex formation of Time... one that we've yet to discover, mainly since we can't get into a black hole to know for sure...





. ..-={Arramon}=-.. .

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. ..-={A}=-.. .

The great attractor is only a local phenomenon (universally speaking, that is).

This is great finally a place to get intelligent answers from knowledgeable people. Now a hard one: As you approach the speed of light time around you slows down, or your time speeds up. The fastest spacecraft can go 40,000 mph. If you where on this craft although it is a small fraction of light speed you would still travel into the future a small fraction of a second (The only calculation I could find is going at 94% of light-speed, time slows down by a factor of four). Now for the question, when you stop would time sync up?

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Why are apples not bananas since they are both fruit?

If you do things right, people won't be sure you've done anything at all.

"The speed of light depends on the material that the light moves through - for example: light moves slower in water, glass and through the atmosphere than in a vacuum. The ratio whereby light is slowed down is called the 'refractive index' of that medium. In general, the difference in the speed of light in other mediums is ignored. "

so that's being very generalized about where you are and what you are travelling through... and with what figure you are using for the speed of light...

"The scientists would say that mass increases with velocity.

It's an increase whose rate itself increases as you approach the speed of light, designated in formulas as "C," and which to you and me is energy going more than 186,000 miles (about seven times around the Earth) per second. This mass gain exists in anything that is not at rest, and since nothing anywhere in the universe is ever at rest, is part of all matter to one degree or another. If you kick the speed of a chunk of matter up a bit, its mass goes up. Not much for most of the time you have your foot on the accelerator, but when you get up close to the velocity of light, the mass gain takes off like a rocket. Your spaceship gets heavier fast.

At 99.9999% of the speed of light, your ship has almost infinite mass. It has become humongously heavy. Since it takes a lot of rocket juice to make something like that speed up, you eventually reach the point where it would take an infinite amount of power to make it go one mile per hour faster. No gas station offers fuel of infinite octane rating, so it can't be done. Nothing made of ordinary matter can attain lightspeed while remaining in the state we call ordinary matter. (And, perhaps, nothing whose characteristics fit the description of an electromagnetic field can drop below lightspeed without becoming what we call matter.)..."

help any? :P

. ..-={Arramon}=-.. .
(this sure is helping me refresh myself some =)

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. ..-={A}=-.. .

However very interesting you are only traveling at 40,000 mph, not the speed of light. Although your mass would increase slightly, it would not affect the question would time sync up or did I just miss the point completely?

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Why are apples not bananas since they are both fruit?

If you do things right, people won't be sure you've done anything at all.

If you stop moving compared to some other object, then your time starts moving at the same rate as the other object. But if you've lost time compared to the other object, you don't get it back.

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Fraser Cain
Publisher
Universe Today - Free space news delivered by email every weekday.

There's a great thought experiment to help understand how time dilation works.

Imagine you're standing beside a train track when a boxcar goes by. Hanging from the roof of the boxcar is a lamp that can be turned on an off.

Now, let's assume that you have super vision and can actually see the individual photons coming out of the lamp, streaming down and hitting the bottom of the boxcar.

First, imagine that the box car is stopped. You turn the light on and then measure the distance a photon travels before it hits the bottom. Obviously, this will be the height of the boxcar, let's say it's 3 metres.

You know that the photon was moving at 300,000 km/s and it traveled a total distance of 3 metres in a fraction of a second.

Next imagine the boxcar is hurtling past you at nearly the speed of light. The photon is emitted from the lamp and travels down to the floor of the boxcar. Now, since you're outside the boxcar, it actually travels diagonally down from your point of view (it moves from the lamp to the floor, and the boxcar is moving horizontally).

Now, if you measured the total path the photon took, it would actually be longer than the distance from the lamp to the floor.

We all know that the speed of light is a constant no matter what speed you're going, so the only way light could have traveled the extra distance is if it had more time to make the journey. In otherwords, time slowed down for the boxcar in relation to you.

That make sense?

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Fraser Cain
Publisher
Universe Today - Free space news delivered by email every weekday.

Before Einstein came along, scientists believed that the speed of light (and indeed anything) could be measured relative to an invisible substance that existed throughout the universe called the "ether". Experiments confirmed Einstein's hypothesis, when it was discovered that the speed of light was always observed to be 300000 km/sec (in space) regardless of the observer's velocity. I.e. if you're travelling in the same direction parellel to a beam of light at 90% of the speed of light, you will still measure the speed of the light beam to be 300000 km/sec. This is because your perception of time is altered (another phenomenon introduced by the Theory of Relativity). My understanding is that the amount of energy needed to increase our velocity by amount x is proportional to the percentage of the speed of light equal to x. So if we were (and all the surrounding astronomical objects which we measure our velocity relative to) moving at 40 percent of the speed of light, our perception of time would be such that an increase in 1 percent of the speed of light would seem to require the same amount of energy as if we were only moving at 30% of the speed of light to begin with. Thus our velocity is and can only ever be measured relative to other objects. Someone correct me if I am wrong.

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Climate Change Australia

Thank you, I have learned a great deal.

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Why are apples not bananas since they are both fruit?

If you do things right, people won't be sure you've done anything at all.

I will abuse of the intelligent people that are answering these questions.

Considering that

1) Everything in the universe is moving in some relative direction and speed.
2) The speed of light is the only thing absolute.
3) That our observation of light movement is distorted by our own relative speed to the light source, and hence, we're not synced (did i get it right?)
4) that gravity acceleration is 1,98... and its propagation speed is around the speed of light.

Here are my questions:

A) is there a way that we can measure the difference between the speed of some object and the speed of a light beam moving in the same direction? or is this out of sync problem impossible to workaround?
B) what is the fastest than two objects have been seen approaching or moving away from one another?
C) is there a limit in acceleration, as it is in velocity?

sorry if its too much, but i didn't want to forget everything that came to my mind as i was writing.

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Only two things are infinite, the universe and human stupidity and I'm not sure about the former.
Albert Einstein

As I understand it If there was a train traveling at 100 miles per hour you fire a gun off the back of that train the bullet will travel 100 miles per hour if you where not on the train it would appear to just stop and fall to the ground if it was fired from the front the bullet would be traveling at 200 miles per hour.

If you are in a car (hard top) and you through a ball in the air it will come back down instead of flying to the back of the car because the ball is traveling at the same speed as the car.

Sorry I am not that good at metaphors.

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Why are apples not bananas since they are both fruit?

If you do things right, people won't be sure you've done anything at all.

CyberJIT,

Our observation of light movement is NOT distorted at all, regardless of our relative speeds. If we're moving towards an incoming beam, or away from it, or parellel to it, we still measure it to have the same relative velocity because our perception of time is altered by our speed. This is not intuitive I know, but it has been backed up by experiments with jets flying at different speeds around the Earth (a few seconds were lost/gained in one case, so you could theoretically increase your life span by living on a jet, ignoring the effect it would have on your health).

Acceleration due to gravity is 9.8 ms^-2 but only on Earth. It is less on Mars and more on Jupiter. There is an element of deception in giving this acceleration an exact value. What if an object more massive than Earth was being attracted towards us due to gravity? What will happen, is that both Earth and the more massive object (x), will move towards a centre of gravity. Object x will still accelerate towards the centre of gravity at 9.8 ms^-2, however Earth will be accelerating towads this point even faster, and their relative acceleration will be the sum of these two accelerations (in different directions obviously).

I'm fairly sure the effects of gravity are propogated at the speed of light, but I'm not entirely sure. I think this is still being tested in experiments.

You raise an interesting point about objects moving away from each other. What if one object is going one direction at 60% of the speed of light, and another object is going in the opposite direction at 60% of the speed of light. Their relative velocity is (in Newtonian physics) 120% of the speed of light. I'm honestly not sure whether this is allowed in general relativity. Surely it would have to be. Perhaps someone can answer this question.

Kashi

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Climate Change Australia

I suggest that you get a popularized treatment of Special relativity from your local library; this will answer most of your questions about relative velocities, etc. Typically, one begins with the Special theory, and then uses a hefty dose of handwaving to give the student a wiff of the General theory. This never works very well, so don't be surprised if none of it makes much sense.

(Handwaving follows

In practice, the time and space coordinates used in general relativity don't correspond to quantities measurable by an observer actually immersed in the system being modelled. An example of this is the "radius" in the solution for a gravity field around a spherical object--e.g., a star. Even when it does--the "universal time" in the solution for the cosmos in the large--it may not be compatible with the spirit of special relativity, where non-co-moving observers have always different "times". What does it mean when a earth-based observer and one orbiting a distant quasar, speeding away from us close to the speed of light, share a common time co-ordinate? This conundrum can make understanding relative velocities in the context of General Relativity counterintuitive, to put it mildly.