Let's see whether such claims can hold up to scrutiny.
Laura Mersini-Houghton lists nine pieces of evidence that she calls “Secret Codes of the Multiverse.” She says these are “nine observable signatures of the entanglement of our universe with other universes.” You can click on the link above to see the entire list.
Secret Codes of the Multiverse?
Those who examine the list looking for sensational cosmic weirdness will be very disappointed. There is nothing in her list of observations that cries out as being evidence of a multiverse or entanglement of our universe with other universes. None of her nine items is anything particularly weird or inexplicable. The items on the list are all pretty much yawners, items not a hundredth as weird and hard-to-explain as, say, dark energy or the Big Bang.
Let us look carefully at the last two items on this list of supposed “Secret Codes of the Multiverse,” two items which have a particularly high bunk content.
Item 8 on this list is listed by Mersini-Houghton like this:
The “tilting” of the gravitational potential of the universe, giving rise to a uniform flow of structure in a particular direction, called the “Dark Flow.”
The hypothesis of “Dark Flow” is the idea that some part of the universe is moving in a strange way. Mersini-Houghton seems to think that this is evidence of some other universe exerting a gravitational pull on part of our universe.
In short, item 8 on Mersini-Houghton's “Secret Codes of the Multiverse” is bunk because the “Dark Flow” phenomenon she cites is not actually occurring.
Now let's look at item 9 on Mersini-Houghton's “Secret Codes of the Multiverse” list. She states it as follows:
The failure of the Large Hadron Collider to detect the breaking of an underlying symmetry of nature known as Supersymmetry (SUSY) at TeV energies.
This piece of supposed “evidence for the multiverse” is actually a non-observation, a null, a piece of non-evidence. It is actually a negative result that is quite contrary to the theoretical underpinnings of Mersini-Houghton's cosmology. She is a proponent of a string theory conception of the multiverse. String theory is built upon the theory of supersymmetry (SUSY). When the Large Hadron Collider failed to find any of the particles predicted by supersymmetry, this was a serious blow to that theory and the string theory on which it is based. The string theory advocates were hoping very much that the Large Hadron Collider would find some of the particles predicted by supersymmetry, so that we might start to get a little evidence for something along the lines of string theory.
So it is quite ridiculous for Mersini-Houghton to be quoting this particular non-observation (the failure to discover particles predicted by supersymmetry) as “a secret code of the multiverse.” It is absurd to cite any non-observation as support for a theory of a multiverse. Consider how laughable is the conversation below.
Student: We tried to get those observations, Professor. But we came up empty-handed, and found nothing.
Professor Jones: That's it! You've found evidence of a multiverse!
Mersini-Houghton's approach seems to be to mainly look for cosmological observational riddles she doesn't understand, and trumpet those as signs of a multiverse, perhaps using some “how else can we explain this mystery” insinuations. I find that approach to be very flawed. There are always dozens of ways to explain any current observational anomaly without resorting to a multiverse.
We don't actually have any evidence for a multiverse, but it might be interesting to consider the question: what type of observations could one make that might be evidence of a multiverse? It would be evidence dramatically different from anything in Mersini-Houghton's list.
Real evidence of a multiverse would not be merely something like an observation of part of our universe flowing in an unexpected way. Such an observation would at best be evidence of one “sister universe” exerting a gravitational effect on our universe. It would not be evidence for an ensemble of universes, each with varying physics and fundamental constants.
Here are two hypothetical ways in which one could actually get evidence of a multiverse:
Method 1: We look up in our telescopes and see radically different physics going on in different parts of the sky. Perhaps in one part of the sky we see light traveling at, say, 50 times the speed of light on our planet; then in some other part of the sky, we see light traveling at one tenth the speed of light on our planet. This might be evidence that we are somehow peering into other universes with different physics from the physics of our universe. But no such observations have ever been reported. We have peered deep into the universe, to the observational limits of our telescopes, and found no such thing. Instead we have found great uniformity of the fundamental physical constants and laws wherever we look.
Method 2: We invent a machine capable of teleporting itself to some other universe. The machine could then make some observations to verify that the other universe had physics radically different from ours. For example, the machine might release a gram of matter on a flat windless plain. If the matter floated up rather than falling down, it might be evidence that the machine was in some weird other universe where gravity acted differently. The machine could then be teleported back to our universe to give us proof of its observations.
There are numerous reasons why it is extremely improbable that Method 2 will ever be applied successfully. The first is that no one has the slightest idea how to teleport a machine to a different universe (black holes won't do the job, since everything tells us that they will completely destroy any machine trying to pass through them). The second is that no one has the slightest idea how to teleport a machine back from another universe to our universe. The third is that if we assume that alternate universes would have a random collection of physics and fundamental constants, it would be more than 99.99999999% likely that a machine teleported to some other universe would be instantly destroyed as soon as it got there, because that universe would be very unlikely to have physics allowing for stable atoms and molecules. It requires a great deal of fine-tuning of various items of physics (such as the charge of the proton and the electron, and the strong nuclear force) for you to even have a universe in which objects as large as a small machine can exist without flying apart.
In short, the prospects of getting any real evidence for a multiverse are very, very slim.