Detecting the presence of other universes

In summary: A causal disconnect is virtually demanded under any reasonable defiinition of a universe.So, while there is a chance that we could detect other pocket universes, it's highly unlikely and there is currently no solid evidence that this is happening. Our best bet is to gain a deeper understanding of high-energy physics.
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Happiness
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In the inflationary Big Bang model, our universe is one of the many pocket universes in the multiverse. How can we detect the existence of the other pocket universes?

I presumed that all the pocket universes exist in the same physical space. So in principle, they can exert influence on one another, gravitationally for instance. But if the expansion rate of the space between two pocket universes exceeds the speed of light, does that mean that the two pocket universes will cease to have any physical effect on each other? In other words, information about the other pocket universes is available in the past but not in the future. Does this result in a paradox?
 
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That is a big question and no satisfactory answer currently exists.
 
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Happiness said:
In the inflationary Big Bang model, our universe is one of the many pocket universes in the multiverse.

I don't think this is strictly true. Does 'regular' inflation predict the same effects that 'chaotic' inflation does?

Happiness said:
I presumed that all the pocket universes exist in the same physical space.

That depends on what you mean by 'multiverse'. See here: http://en.wikipedia.org/wiki/Multiverse#Categories
 
  • #4
Drakkith said:
I don't think this is strictly true. Does 'regular' inflation predict the same effects that 'chaotic' inflation does?

That depends on what you mean by 'multiverse'. See here: http://en.wikipedia.org/wiki/Multiverse#Categories

I'm stating the mainstream view, held by most cosmologists as stated by Alan Guth in his lectures:

 
  • #5
Happiness said:
I'm stating the mainstream view, held by most cosmologists as stated by Alan Guth in his lectures:

In the specific scenario given by Guth, it looks to me like the different 'pocket universes' would indeed exist in the same physical space.
 
  • #6
Reguarding causal connection, causality is the gift that keeps on giving. Once a causal link is established it cannot be severed. There are many galaxies [most in fact] that have receded beyond detectability that we still observe. We will not receive any photons they currently emit, but, we will continue to receive photons they emitted prior to the moment they exited the observable universe forever. They will merely redshift beyond detectability at some point in the distant future. It is not unlike a remote observer watching an astronaut fall into a black hole. The hapless fellow will never appear to reach the event horizon, merely redshift into obscurity. Under most multiverse theories, other universes are causally disconnected at the instant they form. A causal disconnect is virtually demanded under any reasonable defiinition of a universe. Some theorists, such as Laura Mersini-Houghton, hypothesize something like a 'surface of last causal connectivity' could remain as a detectable signature.
 
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Happiness said:
In the inflationary Big Bang model, our universe is one of the many pocket universes in the multiverse. How can we detect the existence of the other pocket universes?
It's highly unlikely that we'll ever be able to find direct evidence. There is some indication that bubble collisions (i.e., collisions with other "pocket universes") in the early universe might be visible in the CMB. But so far there isn't any solid evidence of that occurring.

Our best bet is to gain a deeper understanding of high-energy physics. Spontaneous symmetry breaking is good indirect evidence of other regions of space which have different low-energy laws of physics.

Happiness said:
I presumed that all the pocket universes exist in the same physical space. So in principle, they can exert influence on one another, gravitationally for instance.
Not likely. Even in the many worlds of quantum mechanics, where this is the case, the other worlds are sufficiently isolated that direct evidence is highly unlikely. Other models have the regions with different low-energy physics existing beyond our cosmological horizon where direct detection seems hopeless.
 
  • #8
Chalnoth said:
Not likely. Even in the many worlds of quantum mechanics, where this is the case, the other worlds are sufficiently isolated that direct evidence is highly unlikely. Other models have the regions with different low-energy physics existing beyond our cosmological horizon where direct detection seems hopeless.
But indirectly, it was hypothesized quite some time ago that dark matter may in fact be gravitational energy 'leaking' into our universe from a parallel brane universe, perhaps from short (Planck scale?) hi frequency gravity waves which , unlike light and other electromagnetic radiation, could theoretically penetrate through the higher order dimensions via black holes. Is this hypothesis still being seriously pursued by the m-theory community? I think Hawking is amongst them ( or was).
 
  • #9
Drakkith said:
I don't think this is strictly true. Does 'regular' inflation predict the same effects that 'chaotic' inflation does?
That depends on what you mean by 'multiverse'. See here: http://en.wikipedia.org/wiki/Multiverse#Categories

I think there is some confusion between chaotic inflation and eternal inflation. Even some big name comsologists like George Ellis seem to make this mistake. Eternal inflation leads to a multiverse, chaotic inflation is eternal inflation, but eternal inflation is not necessarily chaotic inflation. See this paper for an explanation:
http://arxiv.org/pdf/gr-qc/0409055.pdf
According to Guth, virtually all models of "regular inflation" are eternal. i think there is something of a myth going around that only chaotic inflation leads to a multiverse, this is not right at all.
see Also Guths paper here:
http://arxiv.org/abs/hep-th/0702178
Of course Guth could turn out to be wrong. but I believe that most people that work on inflation do agree.
 
  • #10
PhanthomJay said:
But indirectly, it was hypothesized quite some time ago that dark matter may in fact be gravitational energy 'leaking' into our universe from a parallel brane universe, perhaps from short (Planck scale?) hi frequency gravity waves which , unlike light and other electromagnetic radiation, could theoretically penetrate through the higher order dimensions via black holes. Is this hypothesis still being seriously pursued by the m-theory community? I think Hawking is amongst them ( or was).
That would be exceedingly difficult to demonstrate. The problem with dark matter stemming from interactions with matter in a closely-located brane is it would be exceedingly difficult to demonstrate this. We could falsify it by detecting a dark matter particle, but if the dark matter particle remains elusive, I'm not sure it would be possible to distinguish between this idea and the WIMP concept, or a number of other, more exotic dark matter ideas.
 
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Chalnoth said:
That would be exceedingly difficult to demonstrate. The problem with dark matter stemming from interactions with matter in a closely-located brane is it would be exceedingly difficult to demonstrate this. We could falsify it by detecting a dark matter particle, but if the dark matter particle remains elusive, I'm not sure it would be possible to distinguish between this idea and the WIMP concept, or a number of other, more exotic dark matter ideas.
Thank you Chalnoth for your valued insight.
 

What is the theory behind the existence of other universes?

The theory of other universes, also known as the multiverse theory, suggests that our universe is just one of many parallel universes that exist simultaneously. These universes may have different physical laws and constants, leading to different versions of reality.

How do scientists detect the presence of other universes?

Currently, there is no empirical evidence or direct observation of other universes. Scientists use theoretical models and mathematical equations to support the existence of other universes. However, some scientists are exploring the possibility of detecting other universes through advanced technology and studying the cosmic microwave background radiation.

Are there any experiments being conducted to detect other universes?

Yes, scientists have proposed several experiments to detect the presence of other universes. These include studying the cosmic microwave background radiation for anomalies, looking for evidence of gravitational waves, and using particle accelerators to test the existence of extra dimensions that could potentially lead to other universes.

What implications would the discovery of other universes have?

The discovery of other universes would have significant implications for our understanding of the universe and our place in it. It could potentially answer questions about the origin of our universe, the existence of other forms of life, and the ultimate fate of our universe. It could also have practical applications in fields such as cosmology, physics, and technology.

Is there a way to travel to other universes?

At this time, there is no known way to physically travel to other universes. The laws of physics as we know them do not allow for such travel. Some theories, such as the concept of a wormhole, propose that it may be possible to travel to other universes, but this is still purely theoretical. More research and advancements in technology are needed to fully understand the possibility of traveling to other universes.

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