Faster than light expansion speeds are standard

In summary, the conversation revolved around the need for a Cosmology FAQ to address common questions and misunderstandings about the expansion of the universe. The participants also discussed how to explain the concept of expansion of space and the apparent superluminal recession speeds of distant objects. Some suggested using analogies such as a balloon expanding, while others preferred more technical explanations. Overall, the consensus was that a FAQ would be beneficial and several individuals were identified as potential contributors.
  • #1
marcus
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We need a stickythread that makes this point. Prominently so it catches newcomers' attention. Otherwise questions about it keep coming up.

If anyone wants to try saying this in an especially clear way, please go ahead. Everybody I can think of has made this point----the mods, the professional astronomers that post here etc.

We should have a Cosmology FAQ. the kindergarten basics. Any one of half a dozen people here could either write the whole thing or contribute paragraphs. Russ, Wallace, SpaceTiger, Kurdt, Janus...

Now I can think of half-a-dozen more! How would YOU explain to a noob that it is standard in cosmology for distances between stationary points to expand FTL?
 
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  • #2
Relativity prohibits v>c for inertial reference frames. Inherent in this requirement is that a relative velocity exists between two points for relativistic effects and boundaries to come into effect. The thing people have trouble getting their head around is that expansion of space does not induce a relative velocity. A way of thinking of this is a sheet of cloth with a 1D axis on it. If you make a tear and sew in new cloth along a line, the points a and b on the axis have moved apart a bit but their distance is still a-b and are anchored in space. Simply looking at the mathematics of special relativity this is allowed because again we are only concerned with relative movement IN SPACE if space itself expands there's nothing to say that two points can be 'carried away' from each other faster than the speed of light. We don't witness this expansion on a local scale because of gravitational effects. The mass of galaxies and clusters of galaxies like our own local group reigns in the effects of this but the drift of galactic clusters shows clear indication of this happening all the time.

Thats as best as i can put it for now :P
 
  • #3
FunkyDwarf said:
... Simply looking at the mathematics of special relativity this is allowed because again we are only concerned with relative movement IN SPACE if space itself expands there's nothing to say that two points can be 'carried away' from each other faster than the speed of light. We don't witness this expansion on a local scale because of gravitational effects. ...

That works for me. Does anybody have problems with that way of putting it, or anything to add?
 
  • #4
Personally I don't like the 'space can expand faster than light' thing since it gives the idea that 'space' is something that can do things and helps reinforce the (incorrect) notion that the expansion of space causes galaxies to move apart.

In any case I've been waiting till the wiki style 'content library' appears then I think we should mine old threads for the basis of the content to go in this, with some polishing and new additions.
 
  • #5
John Baez has already done this on his website with great clarity and expertise. A link there would be sufficient, IMO.
 
  • #6
I find the balloon analogy to be helpful. Exaggerating the expansion speed for simplicity -- if the balloon (universe) is expanding at a rate such that distance between objects increases by say, one percent per year, then after 100 years everything will be twice as far away as it was. So an object that was 200 light years away on this giant balloon 100 years ago is now 400 light years away. It has apparently moved 200 light years in 100 years, a recession speed of twice the speed of light. With respect to local space it remained stationary, there is just more space due to the expansion of the universe. If the universe is large enough and expanding even at a slow rate, superluminal recession speeds at great distances are unavoidable.
 
  • #7
marcus said:
We need a stickythread that makes this point. Prominently so it catches newcomers' attention. Otherwise questions about it keep coming up.

If anyone wants to try saying this in an especially clear way, please go ahead. Everybody I can think of has made this point----the mods, the professional astronomers that post here etc.

We should have a Cosmology FAQ. the kindergarten basics. Any one of half a dozen people here could either write the whole thing or contribute paragraphs. Russ, Wallace, SpaceTiger, Kurdt, Janus...

Now I can think of half-a-dozen more! How would YOU explain to a noob that it is standard in cosmology for distances between stationary points to expand FTL?
I agree that a faq would be a good idea - there are lots of questions people have that are repeated over and over again.

As you probably know, I am an engineer and an amateur astronomer, not a professional physicist/academic. While I do agree that such a faq should probably be very basic (and such explanations are what I try to contribute when I see people getting hung up on or confused by the minutae), I know a lot of the higher level guys worry about oversimplification of the issues. It's a tough balance. I'll bring the issue up with the other mods.
 

1. How is faster than light expansion possible?

Faster than light expansion is possible through the theory of relativity, which states that the fabric of space-time can expand faster than the speed of light without violating any physical laws.

2. What evidence supports the idea of faster than light expansion?

The most compelling evidence for faster than light expansion comes from observations of distant galaxies, which show that they are moving away from each other at faster than light speeds. This is known as the phenomenon of cosmic inflation.

3. Are there any exceptions to the rule of faster than light expansion?

While faster than light expansion is widely accepted as a valid concept in physics, there are some theories that challenge it. For example, some theories propose the existence of a hypothetical "warp drive" that could potentially travel faster than light.

4. How does faster than light expansion affect our understanding of the universe?

Faster than light expansion is a crucial aspect of the Big Bang theory, which explains the origin and evolution of the universe. It also plays a role in our understanding of the structure and expansion of the universe, as well as the behavior of light and other fundamental particles.

5. Can humans ever travel at faster than light speeds?

At this point in time, it is not possible for humans to travel at faster than light speeds. The laws of physics, including the theory of relativity, currently prevent any object with mass from achieving this speed. However, ongoing research and advancements in technology may one day make it possible.

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