Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 08/04/2013 15:30:01
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Chris Martin asked the Naked Scientists:
Many astronomers any physicists talk about objects in the Universe travelling at nearly the speed of light, for example the gas jets leaving a quasar, the matter in an accretion disk circulating around a black hole or the matter travelling away from a supernova, but my question is what is this speed relative to? Is there a standard "stationary" object in the universe which all these examples relate to? Otherwise these statements are meaningless.
Thanks
Chris Martin
Mark, Somerset.
What do you think?
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Every object is considered to be stationary. You can set a clock with another clock. The idea is just to match two objects to each other so that they start off the same.
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Chris Martin asked the Naked Scientists:
Many astronomers any physicists talk about objects in the Universe travelling at nearly the speed of light, for example the gas jets leaving a quasar, the matter in an accretion disk circulating around a black hole or the matter travelling away from a supernova, but my question is what is this speed relative to? Is there a standard "stationary" object in the universe which all these examples relate to? Otherwise these statements are meaningless.
Thanks
Chris Martin
Mark, Somerset.
What do you think?
No. There is no standard object with which everything elses velocity is measured against. That would imply absoulte space which doesn't exist. Typically when people are talking about things moving near the speed of light they have a frame of reference in mind. E.g. gas shooting out of a quasar is moving near the speed of light with respect to a frame of reference inwhich the quasar is at rest.
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Mazur and Chapline, and, I think others, suggested that the Universe might be spinning on an axis. Is that idea still current in scientific circles? If it were the case it would create a place in the Universe that would be special and stationary.
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Mazur and Chapline, and, I think others, suggested that the Universe might be spinning on an axis. Is that idea still current in scientific circles? If it were the case it would create a place in the Universe that would be special and stationary.
If that were the case, exactly where would this spot be and to what do we compare it's motion? I agree with Pmb on this issue.
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From what I understand, spinning (net angular momentum) could be detected because it would mean we're not in an inertial reference frame. For example, without looking outside the earth at all, we can tell we're rotating due to the Coriolis effect.
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For example, without looking outside the earth at all, we can tell we're rotating due to the Coriolis effect.
True, but can we observe any such effect arising from the rotation of our galaxy? Without looking outside the galaxy, could we tell it was rotating?
If the Universe were rotating, could we tell; without being able to look outside the Universe? Unless, of course, we were able to see the axis of rotation, which, obviously, we are not.
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More than that, if I remember right a spinning universe would allow for time travel, according to some interpretations at least. So it better not spin :) http://bigthink.com/dr-kakus-universe/is-time-travel-possible-part-ii also there was some limited evidence for a preferred spin direction for galaxies, implying that the universe might have been spinning at some origin according to the Sloan Digital Sky Survey. But then we have this other research of galaxies and stars in where we all are invited to help define what we see in the sky. The http://www.galaxyzoo.org/
They found it not to be spinning http://www.universetoday.com/13340/galaxy-zoo-results-show-that-the-universe-isnt-lopsided/ which is good for me, and the universe at large :) As we then agree, ahem.
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For example, without looking outside the earth at all, we can tell we're rotating due to the Coriolis effect.
True, but can we observe any such effect arising from the rotation of our galaxy? Without looking outside the galaxy, could we tell it was rotating?
Sure. Look at how light propagates from distant points. You should see it curve in a way that's consistent with us moving around the galactic center.
If the Universe were rotating, could we tell; without being able to look outside the Universe? Unless, of course, we were able to see the axis of rotation, which, obviously, we are not.
I'm less confident on this one, but you should be able to look at large scale features such as galactic rotation and the CMBR. If the universe were rotating it should be visible in these.
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It is a da*n tricky one considering the universe is isotropic and homogeneous. That means that we have no preferred place of observation from where to define a center for this 'spinning universe'. The intuitive idea of a spin is related to a disk spinning for example, or a ball. But assume that we have a spin, and still a isotropic homogeneous universe, how would you find it?
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Now if the quasar eject was moving at the light of speed with reference to the quasar, then an observer watching the quasar in motion would note the quasar eject moving at a speed greater than that of light... Anyone please illuminate !!