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Chinnywilla
2011-Mar-09, 02:18 AM
Consider for a moment the following scenario:

Imagine two earth bound astronomers gazing through powerful telescopes at a planet in distant galaxy approximately 10 billion light years away.

One astronomer packs up his telescope and takes it to his local ‘instantaneous matter transporter’ facility. The transporter beams the astronomer and his telescope across the Universe to the small planet in the distant galaxy.

The earthbound astronomer points his telescope to where his colleague has materialised, only to realise that he will have to wait 10 billion years for the light of the event to reach earth.

The distant astronomer sets up his telescope and points it towards earth. He can see nothing. The earth is approximately 5 billion years old. Light from the formation of the earth will not reach him for another 5 billion years. He will not see the light from his colleague for a further 5 billion years.

Other than the fictitious ‘matter transporter’ and impossible telescopes, there is nothing surprising in the above until one considers the implications of the distant astronomers observations.

The distant astronomer is clearly aware that the earth exists. He knows it is made from ordinary baryonic matter. Yet, from his perspective, he is completely unable to prove or disprove its existence. He will probably be aware that no matter how sensitive his instruments are he will never be able to detect the existence of the earth.

To him, the earth would appear as dark matter.

The earth bound astronomer may have a similar thought. When scanning the night sky with his telescope he is aware that he can only see into the past. The greater distances he probes, the further back in time he goes. Because of the finite speed of light, he cannot see the entire Universe in its current state, he cannot yet detect baryonic mass whose light is yet to reach the earth.

To him, the Universe would appear to be filled with dark matter.

stutefish
2011-Mar-09, 03:19 AM
Hello, Chinnywilla, welcome to BAUT!

What does your theory say about things like the Bullet Cluster, where our telescopes can detect dark matter's gravitational effect on baryonic matter?

ETA: I mean, you seem to be under the impression that dark matter is undetectable. But this is not true. In fact it is quite detectable, by virtue of its significant gravitational effects.

In your thought experiment, the one observer must wait millions of years to receive photons from Earth.

In our real observations of dark matter, we're not waiting for any photons at all, and we've already observed the gravitational effects (by receiving photons of the baryonic matter affected by the gravity of the dark matter).

Your proposal seems to assume that the photons from the dark matter in the Bullet Cluster haven't reached us yet. But the photons from the baryonic matter in the Bullet Cluster are here already, with more arriving all the time.

If dark matter emitted photons (as you seem to imply), then the photons from the dark matter in the Bullet Cluster should have reached us at the same time as the photons from the baryonic matter. But no dark matter photons have reached us from the Bullet Cluster. This is what puts the "dark" in "dark matter".

On the other hand, the photons from the baryonic matter in the Bullet Cluster shows us that there's an additional gravitational effect there, not accounted for by the baryonic matter whose photons we've received. That is what puts the "matter" in "dark matter".

So there you go: Dark because it doesn't emit photons. Matter because it causes observable gravitational effects in baryonic matter.

Is your proposal that photons from dark matter are substantially slower than photons from baryonic matter?

pzkpfw
2011-Mar-09, 03:26 AM
To him, the earth would appear as dark matter.

No. In your scenario he "knows" Earth is there, because he knows it's there. That's circular and doesn't match reality.

Dark matter is postulated as a cause for what is seen by astronomers. That is, it's effects.

A kind of analogy, would be if your distant astronomers could see Earths' Moon orbiting something, but couldn't see Earth. Then they might postulate some invisible object with mass.

Or in other words, if your teleported astronomer was instead some astronomer who was already at that distanct location, how would they know Earth was there? They can't just imagine it; and neither do astronomers just imagine Dark matter. They use it to explain something... there's a something to explain.

Chinnywilla
2011-Mar-09, 11:14 AM
Thanks for the quick replies guys.

My central hypothesis was that dark matter doesn’t exist, it is merely ordinary matter that exists at this instant in time but because of the vastness of space and the relatively slow speed of light this matter is yet to be detected and therefore cannot be accounted for.

You are both quite correct in your reasoning. For my hypothesis to carry any weight, the speed of light and the ‘speed’ of gravitational influence would have to be significantly different. Since they are not, the hypothesis is clearly wrong.


I rather think my hypothesis isn’t worth the pixels its written with and is certainly busted!

baric
2011-Mar-09, 02:31 PM
Other than the fictitious ‘matter transporter’ and impossible telescopes, there is nothing surprising in the above until one considers the implications of the distant astronomers observations.

Q1) Why should anyone be surprised by any sort of implications as the result of fictitious and impossible causes?

Shaula
2011-Mar-09, 03:21 PM
Q1) Why should anyone be surprised by any sort of implications as the result of fictitious and impossible causes?
It's a thought experiment. You often dream up impossible tools to do strange jobs and see if they give an insight into some set of physical laws. Then you go back and find a way to test your insight with more accessible tools. Maxwell's demon, for example.

Jim
2011-Mar-09, 04:49 PM
... the hypothesis is clearly wrong. ...

Based on this statement from the OP (Welcome to BAUT, BTW!) I am closing this thread. Chinnywilla, if you change your mind and wish to re-present and defend your idea, report this post (click the triangle with the !) and ask for the thread to be reopened.