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Chris Hadfield
Retired Canadian Astronaut & Author
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The science of expansion: Andromeda, gravity, and the ‘Big Rip’

If the universe is expanding in all directions, why is Andromeda hurtling toward the Milky Way?

MICHELLE THALLER: One of the questions I get asked most commonly as an astronomer is if almost all the galaxies in the universe are flying away from us in space, why is the Andromeda Galaxy getting closer to us? Does that somehow mean that the Big Bang works differently in different parts of the universe? And the answer simply is: no. Space is expanding because of the Big Bang. All of space is expanding in every direction all at once and from our viewpoint that means that it looks like all the other galaxies are moving away from us. But not all the universe around us appears to be expanding. For example, the Earth doesn't seem to be getting any farther away from the Sun. The Sun is not getting any farther away from our galaxy. Thank about smaller scales, like your body; your body (luckily) is not expanding along with the universe. And the reason is that the expansion of the universe is actually a pretty gentle force; you really only notice it out in the middle of nowhere in the vast reaches of space between the galaxies. There's a lot of space out of there, so there is a lot of space to expand and so you really notice this expansion.

But there are things that are stronger than the expansion force. For example, my body is held together by chemical forces and by electrical forces. That is much, much stronger than the tiny little push that space has to expand inside me. I hold together very well. One of the analogies I think about is: You could try to push over the Empire State Building by blowing on it. You are actually exerting a force on the Empire State Building by blowing on it, you can measure that force, but you're not going to blow over the Empire State Building. There are things that are much stronger than this omnipresent but gentle force of the expansion of the universe. The gravity between the Sun and the Earth is stronger than space's pressure to expand over that scale. The force of gravity is stronger than the outward push of the expansion of the universe. That's also true of the galaxy, we are held in orbit around the center of the galaxy. Gravitationally, that's much stronger than any expansion force.

So why is Andromeda different? Andromeda is close enough to our Milky Way Galaxy that the gravity between the two is strong enough for the two to start moving together. Yeah, space is expanding between us and the Andromeda Galaxy, but gravity is accelerating Andromeda toward us faster than that expansion. And, in fact, that means that Andromeda is going to collide with the Milky Way in a couple billion years. And we see this happening all over the universe. There are clusters of galaxies where the galaxies are close enough together that they are merging and colliding. When galaxies are far enough away from each other that the gravitational force is weaker, the acceleration due to gravity is weaker than the outward expansion, then they start moving away. Now one of the intriguing things is that we don't know what the future holds when it comes to the expansion force of the universe. Just recently in the last couple of decades we've measured that the universe is not only expanding but it's actually accelerating. In some ways that force is getting stronger and stronger all the time and we don't know whether that will stop or whether that will stay constant or whether in fact that expansion force will keep getting stronger.

Will there be a day when the expansion force of the universe is strong enough that our galaxy does start to expand and the stars start to move farther and farther away from each other? Will there come a time when the Sun and the Earth are actually pulled apart by the expansion of the universe? And perhaps most intriguingly, will there ever come a time when the expansion of the universe is strong enough to rip apart your atoms, to actually have matter disappear into a little soup of organic particles? We call this idea the Big Rip and it's one of the possible ends of the universe – that the expansion force will eventually get so strong it literally rips everything apart. We don't know whether this will happen yet so we have a lot more investigating to do about this thing called dark energy that may be accelerating the universe and that's one of the best questions we're trying to answer right now.

  • The Andromeda Galaxy and our Milky Way are on a collision course that will obliterate life on Earth 4.5 billion years from now.
  • The universe is expanding in all directions, all at once – so why are Andromeda and the Milky Way drawing nearer? The gravity between them is a stronger force than expansion.
  • The rate of expansion is accelerating. If it continues to speed up, its force may become strong enough pull things apart that are currently held together by superior forces: Our galaxy, the solar system, and even the atoms in our bodies. That possible ending to the universe is known as the 'Big Rip'.

A new hydrogel might be strong enough for knee replacements

Duke University researchers might have solved a half-century old problem.

Photo by Alexander Hassenstein/Getty Images
Technology & Innovation
  • Duke University researchers created a hydrogel that appears to be as strong and flexible as human cartilage.
  • The blend of three polymers provides enough flexibility and durability to mimic the knee.
  • The next step is to test this hydrogel in sheep; human use can take at least three years.
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Predicting PTSD symptoms becomes possible with a new test

An algorithm may allow doctors to assess PTSD candidates for early intervention after traumatic ER visits.

Image source: camillo jimenez/Unsplash
Technology & Innovation
  • 10-15% of people visiting emergency rooms eventually develop symptoms of long-lasting PTSD.
  • Early treatment is available but there's been no way to tell who needs it.
  • Using clinical data already being collected, machine learning can identify who's at risk.

The psychological scars a traumatic experience can leave behind may have a more profound effect on a person than the original traumatic experience. Long after an acute emergency is resolved, victims of post-traumatic stress disorder (PTSD) continue to suffer its consequences.

In the U.S. some 30 million patients are annually treated in emergency departments (EDs) for a range of traumatic injuries. Add to that urgent admissions to the ED with the onset of COVID-19 symptoms. Health experts predict that some 10 percent to 15 percent of these people will develop long-lasting PTSD within a year of the initial incident. While there are interventions that can help individuals avoid PTSD, there's been no reliable way to identify those most likely to need it.

That may now have changed. A multi-disciplinary team of researchers has developed a method for predicting who is most likely to develop PTSD after a traumatic emergency-room experience. Their study is published in the journal Nature Medicine.

70 data points and machine learning

nurse wrapping patient's arm

Image source: Creators Collective/Unsplash

Study lead author Katharina Schultebraucks of Columbia University's Department Vagelos College of Physicians and Surgeons says:

"For many trauma patients, the ED visit is often their sole contact with the health care system. The time immediately after a traumatic injury is a critical window for identifying people at risk for PTSD and arranging appropriate follow-up treatment. The earlier we can treat those at risk, the better the likely outcomes."

The new PTSD test uses machine learning and 70 clinical data points plus a clinical stress-level assessment to develop a PTSD score for an individual that identifies their risk of acquiring the condition.

Among the 70 data points are stress hormone levels, inflammatory signals, high blood pressure, and an anxiety-level assessment. Says Schultebraucks, "We selected measures that are routinely collected in the ED and logged in the electronic medical record, plus answers to a few short questions about the psychological stress response. The idea was to create a tool that would be universally available and would add little burden to ED personnel."

Researchers used data from adult trauma survivors in Atlanta, Georgia (377 individuals) and New York City (221 individuals) to test their system.

Of this cohort, 90 percent of those predicted to be at high risk developed long-lasting PTSD symptoms within a year of the initial traumatic event — just 5 percent of people who never developed PTSD symptoms had been erroneously identified as being at risk.

On the other side of the coin, 29 percent of individuals were 'false negatives," tagged by the algorithm as not being at risk of PTSD, but then developing symptoms.

Going forward

person leaning their head on another's shoulder

Image source: Külli Kittus/Unsplash

Schultebraucks looks forward to more testing as the researchers continue to refine their algorithm and to instill confidence in the approach among ED clinicians: "Because previous models for predicting PTSD risk have not been validated in independent samples like our model, they haven't been adopted in clinical practice." She expects that, "Testing and validation of our model in larger samples will be necessary for the algorithm to be ready-to-use in the general population."

"Currently only 7% of level-1 trauma centers routinely screen for PTSD," notes Schultebraucks. "We hope that the algorithm will provide ED clinicians with a rapid, automatic readout that they could use for discharge planning and the prevention of PTSD." She envisions the algorithm being implemented in the future as a feature of electronic medical records.

The researchers also plan to test their algorithm at predicting PTSD in people whose traumatic experiences come in the form of health events such as heart attacks and strokes, as opposed to visits to the emergency department.

Hints of the 4th dimension have been detected by physicists

What would it be like to experience the 4th dimension?

Two different experiments show hints of a 4th spatial dimension. Credit: Zilberberg Group / ETH Zürich
Technology & Innovation

Physicists have understood at least theoretically, that there may be higher dimensions, besides our normal three. The first clue came in 1905 when Einstein developed his theory of special relativity. Of course, by dimensions we’re talking about length, width, and height. Generally speaking, when we talk about a fourth dimension, it’s considered space-time. But here, physicists mean a spatial dimension beyond the normal three, not a parallel universe, as such dimensions are mistaken for in popular sci-fi shows.

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How often do vaccine trials hit paydirt?

Vaccines find more success in development than any other kind of drug, but have been relatively neglected in recent decades.

Pedro Vilela/Getty Images
Surprising Science

Vaccines are more likely to get through clinical trials than any other type of drug — but have been given relatively little pharmaceutical industry support during the last two decades, according to a new study by MIT scholars.

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